The chemical combination which forms the infinite variety of substances in the organic and inorganic creation consists in an intimate union of their ultimate atoms which produces substances differing from their constituent parts in every respect except gravitation, the sum of the weights of their constituent parts being invariably equal to the weight of the resulting substance. Thus the chemical union of oxygen and hydrogen forms water, and the weight of the water so formed is exactly equal to the sum of the weights of the two gases.

All chemical changes whether of analysis or composition are subject to definite unalterable laws of weight, measure and number; nothing is by chance or casual, the relative weights of the invisible atoms of matter, and their combination in definite proportions reveal the laws which prevailed in the primeval structure of created things. By the wonderful discovery of these laws Dr. Dalton has placed chemistry on a strictly numerical basis.

The chemical union of different kinds of atoms and volumes of matter in the definite proportions of whole numbers entirely changes their character and properties, as for example the chemical combination of one atom of hydrogen and one atom of oxygen into water. The condensation is often unexpected and wonderful; two different liquids are often condensed into a solid, and the result of the chemical combination of two different gases or vapours in quantitative proportions may be solid, liquid or aëriform, a fact which could only have been discovered by experiment. The powers of the atoms are changed and often highly exalted by chemical union as in ammonia, a chemical compound of three atoms of hydrogen and one of nitrogen, which absorbs 1,195 times more radiant heat than its constituents whether simple or mixed. During chemical combination light and electricity are often evolved, heat always. The quantity given out is exactly proportional to the energy of the chemical action, and is often so great and so rapidly evolved as to produce an explosion by the sudden expansion of the air around. Whatever the temperature may be, which is given out during the union of the atoms, the very same quantity of heat is requisite to dissolve their union, and the atoms are separated in the same definite proportions in which they were combined.

Voltaic electricity both combines and resolves substances into their component parts, strictly according to the law of definite proportions. It combines eight parts by weight of oxygen and one part by weight of hydrogen into water; and again when it decomposes water, one part by weight of hydrogen is given out at the negative pole of the battery, and eight parts by weight at the positive or zinc pole. For an electric current weakens or neutralizes the force of affinity in one direction and strengthens it in the other, so that the heterogeneous atoms of the substance under its influence have a tendency to go in different directions and appear at opposite poles. Mr. Faraday has established as a general law, that the quantity of electricity requisite to unite the atoms of matter, is precisely equal to the quantity requisite to separate the same atoms again. Electro-chemical action, or the power of electricity to combine and separate the heterogeneous atoms of matter, is in direct proportion to the absolute quantity of electricity that passes in the current. Hence the superior analytical power of voltaic over static electricity, which has enormous intensity, but is very small in quantity. The electric current separates molecular combinations which yield to no other means: it is the most powerful instrument of analysis; light is the most delicate.

Two simple substances are only capable of a certain number of chemical combinations, which form a regular series of new substances; as for example oxygen and nitrogen. Two measures of nitrogen gas will unite with one measure of oxygen to form the protoxide of nitrogen; with two measures of oxygen it unites to form the binoxide of nitrogen; with three measures of oxygen it forms the hyponitrous acid; with four it forms nitrous oxide; and with five measures of oxygen it forms nitric acid. Thus there are five compounds of nitrogen and oxygen, no more. Affinity of kind is merely the attraction of one element or atom of matter for another; affinity of degree consists in the grades and limits of combination; the preceding series is of the fifth degree; the limit is the last term, for no further combination of these two gases can take place, and these are accomplished by art. All the five substances are deleterious, most of them deadly poisons, for the protoxide of nitrogen, which is the laughing gas, could not be long inhaled with impunity. For a long time the middle term of the preceding series was wanting, but Gay-Lussac formed it by attending to the laws of definite proportion and sequence.

The atoms of different kinds of matter possess an affinity, or attractive force, which binds them together chemically in different and very unequal degrees. Two substances may unite and form a third differing from both, as water does from oxygen and hydrogen; but if a new substance be added which has a greater attraction for one of the substances than for the other, it will dissolve their union, combine with that for which it has the strongest attraction, and set the other free. Thus the metal potassium, which has a greater attraction for oxygen than it has for hydrogen, decomposes water, combines with the oxygen, and sets the hydrogen free. Both chlorine and ozone have the property of liberating the iodine in a weak solution of the iodide of potassium; the liquid stains starch blue, a proof of the free iodine. The facility with which acids and alkalies combine affords the means of eliminating either the one or the other from a compound so as to liberate what remains.

The constituents of compound substances may be separated from one another by a variety of means depending upon their greater or less fusibility, volatility, and other properties. Water, acids, alcohols and other liquids hot or cold, different degrees of temperature, sublimation, solution, distillation, evaporation, together with static and voltaic electricity, are the most powerful means of analysis.

But the animal and vegetable creation rear their fabrics by a synthetic process. A plant after having absorbed carbonic acid and water, decomposes the carbonic acid, returns the oxygen to the atmosphere, and combines the carbon and water into wood, leaves, and a variety of organic substances. Now MM. Berthelot, Wöhler, and other distinguished chemists, by following this example of nature, have established a system of synthetic chemistry, by which they have produced from the chemical combination of the three elementary gases and carbon alone more than 1,000 complete organic substances, precisely the same with those formed within the living plants and animals. Yet we are as far as ever from any explanation of the mystery of life, whether animal or vegetable.

Carbon and hydrogen will not combine at any artificial heat however great; but when the electric arc between highly purified charcoal terminals passes through hydrogen gas, acetylene, a new carburet of hydrogen, is formed, consisting of four equivalents of carbon and two of hydrogen. This substance, which no organized being is capable to form, was discovered by M. Berthelot, and being assumed as a base, yielded an extensive series of organic substances. Thus when two atoms of carbon are added to acetylene it becomes olefiant gas; when two equivalents of oxygen are added to olefiant gas, the result is alcohol, which is transformed into acetic acid by the addition of two atoms of oxygen, and from this by a similar process have been obtained the malic, tartaric, succinic, and the other acids; glycerine also, which is the sweet principle of the oils, wax, essential oils, the perfumes of fruit and flowers, the principle of the balms, the essential oil of mustard, and numerous other organic substances, simply from carbon, oxygen and hydrogen; but nitrogen was introduced by combining alcohol with ammonia, an inorganic substance consisting of three equivalents of hydrogen and one of nitrogen, from whence a vast number of nitrogenized substances were derived, both animal and vegetable.

Chemical combination, which has from the beginning of created things, and still is, building up organic and inorganic matter in the earth, in the air, and the ocean, exerts forces of transcendent power, though silent, unperceived, and for the most part unknown. Professor Tyndall has given a striking instance of this in water, the most simple compound of oxygen and hydrogen, a constituent alike of organic and inorganic nature. ‘In the combustion of the two gases to form a gallon of water weighing ten pounds, an energy is expended, the atoms clash together with a force, equal to that of a ton weight let fall from a height of 23,757 feet; and in the change from the state of vapour to water, an energy is exerted equal to that of a ton weight falling from a height of 3,700 feet, or of a hundredweight falling from a height of 74,000 feet. The moving force of the stone avalanches of the Alps is but as that of snowflakes compared with the energy involved in the formation of a cloud. In passing finally from the liquid to the solid state,’ that is from water to ice, ‘the atoms of ten pounds exercise an energy equal to that of a ton weight falling down a precipice of 550 feet of perpendicular height.’

From Mr. Joule’s investigation of the relation existing between chemical affinity and mechanical force, it appears that when affinity is feeble it can be overcome mechanically. He formed amalgams of different metals, that is he combined them with mercury, by electricity. The affinity of iron for mercury is so feeble that the amalgam is speedily decomposed when left undisturbed by the pressure of the atmosphere, and if a greater pressure be added, almost all the mercury is driven out. The efficacy of mechanical force to overcome feeble chemical affinities is strikingly illustrated by the amalgam of tin, out of which nearly the whole of the mercury is driven by long continued pressure. In these cases the force of affinity did not amount to chemical equivalency, otherwise the mercury could not have been driven out by so small a force. Instances from the weakest to the strongest affinity show that it is only when the power reaches a definite point that the law of chemical equivalents comes in. The intense energy which then begins to be exerted has just been shown.

It is vain to hope for a knowledge of the absolute weight of the ultimate atoms of matter, and nothing seems to be more beyond the power of man than to determine even their relative weights; yet the definite proportions in which they combine have enabled him to do so. Thus, an atom of oxygen unites with an atom of hydrogen to form water; but as every drop of water, however small, contains eight parts by weight of oxygen, and one part by weight of hydrogen, it follows that an atom of oxygen is eight times heavier than an atom of hydrogen. Now, since hydrogen gas is the lightest body known, its atom has been assumed as the unit of comparison. Hence, if the unit of hydrogen be represented by 1, that of oxygen may be represented by 8. Again, carbonic acid gas contains six parts by weight of carbon, and eight parts by weight of oxygen, and as an atom of oxygen is eight times heavier than an atom of hydrogen, therefore an atom of carbon is six times heavier than an atom of hydrogen, and consequently may be represented by 6. In this manner the relative weights of many substances have been determined. But the property of isomorphism also affords the means of ascertaining the atomic weights of certain substances with unerring certainty. It is exactly the contrary of dimorphism, for in the latter substances are chemically the same under different forms; whereas isomorphic bodies are chemically different under the same form. Now the peroxide of manganese contains one atom of oxygen for one atom of metal; but in 100 parts of the protoxide there are 21·94 parts of oxygen and 78·06 of manganese. Comparing these numbers with 8 the atomic weight of oxygen, the result is 28 the weight of an atom of manganese. The same number is obtained from two other isomorphic compounds of oxygen and manganese, which proves the accuracy of this result. The atomic weights of many bodies have been determined, of which the following are the most important.

In the determination of atomic weights a few cases have occurred of fractional numbers, and although it cannot yet be affirmed that no such cases exist, yet it seems to be established by the new and more perfect analyses of MM. Dumas, Isidore, Williamson, and others, that the atomic weights of substances compared with an atom of hydrogen are in whole numbers.

This law leads to very important results. For example, the equivalent weights of the chemical elements of bodies derived from their specific gravities are either identical with, or simple multiples or sub-multiples of, their relative weights. Thus the specific gravity of hydrogen is 0·0693, and that of oxygen is 1·111; hence taking hydrogen as the unit of comparison, it is easy to see that 0·0693 : 1·111 :: 1 : 16, the simple multiple of 8, the relative atomic weight of oxygen. In fact since each substance has its own specific gravity or weight, that weight must depend upon the weight of its atoms, so that the weights of equal bulks of different substances are proportional to the weights of their atoms, and thus a relation is established between the atomic weights and specific gravities of bodies, so that one being given the other may be found.

Atoms like their substances have many different capacities for heat and electricity. It was proved by MM. Petit and Dulong, that specific heat, or the quantity of heat required to raise a simple substance to a given temperature, is inversely as the weight of its atoms, so that the specific heat or repulsive force of simple substances multiplied by their atomic weights is a constant quantity. Such is the condition requisite for the equilibrium or equality of force; or the law may be thus expressed: A given quantity of heat will raise to the same number of degrees a portion of every simple substance represented by its atomic weight. For instance, the atomic weight of sulphur is 16, that of zinc 32·5; hence it requires twice as much heat to raise a pound of sulphur ten degrees as it does a pound of zinc. It has also been proved that the atoms of compound bodies of analogous composition are endowed with the same capacity for heat, so that there is a perfect correspondence between the weight of atoms and their specific heat. The numbers representing the atomic weights derived from the specific heat of bodies are connected with their equivalent atomic weights by the simple ratios of equality, multiples or sub-multiples.

Mr. J. Croll has made experiments showing that the specific heat of compound gases and liquids is generally less, and those of solids more, than that of their component elements, which is contrary to the hitherto received opinion. Moreover it appears that the changes in the specific heat of bodies which occur during combination are not only due to chemical action, but also to molecular changes; the real specific heat of a simple atom probably remaining the same under all conditions.

Mr. Faraday has proved that the specific electricity of different substances is also in proportion to their atomic weights, that is to say, a given quantity of electricity will separate combined substances into parts represented by their atomic weights. For example, 32·5 parts of zinc will generate voltaic electricity enough to separate nine parts of water into eight parts of oxygen and one part of hydrogen gas. The weights thus derived from decomposition are exactly the same with those determined by composition, and thus the atomic weights derived from electro-decomposition accord exactly with those obtained from chemical composition. Moreover, Mr. Faraday, as already mentioned, proved that the very same quantity of electricity necessary to decompose a body into its elementary atoms, is requisite to unite them again. The analysis and synthesis of compound matter, solid or fluid, show a constant and definite proportion of the component elements expressed by number, and by an equivalent or multiple ratio of parts in every chemical change.

The atomic theory unites, by a common bond, specific gravity, chemical affinity, heat, and electricity. Taking atmospheric air at the temperature of 60° Fahr. and a barometric pressure at 30 inches as the standard unit of specific gravity; the quantity of heat required to raise a volume of water 1° Fahr. as the unit of specific heat; hydrogen gas as the unit of atomic weight; and atomic electro-chemical electricity as the unit of specific electricity, the following numbers have been established:

The distances between the atoms of the gases are equal, hence the atomic weights of simple gases are proportional to their densities; and for the same reason, equal volumes of the same fluid contain an equal number of atoms, and the number of atoms in the same volume of different fluids is in the simple ratio of one to one, one to two, one to three, &c.

It follows from the atomic theory that the number of atoms in equal weights of any two solid substances, is in the inverse ratio to the weights of these atoms. Now since the bodies that have the greatest specific gravities are the heaviest, if the specific gravities and atomic weights of equal bulks of two simple substances be known, the relative number of atoms they contain may be found. For the density divided by the atomic weight of the one, is to the density divided by the atomic weight of the other, as the number of atoms in the first to the number of atoms in the second. By the preceding law it is found that in equal bulks of the three metals, sodium, platinum, and potassium, platinum contains five times as many atoms as sodium, and ten times as many as potassium. When substances which have strong analogous qualities are compared in this manner, the results are either equality, or a simple ratio.

It has already been mentioned that the protoxides of iron, copper, zinc, nickel and manganese, have the same form, and contain the same quantity of oxygen, but differ in the respective metals that are combined with it; and by the preceding law it appears that equal bulks of these isomorphous bodies contain also the same number of atoms.

Mr. Hermann Kopp has proved that the atomic weight of a substance divided by the specific gravity, that is to say, its atomic volume, is the same for all isomorphic bodies simple and compound, and as a general law that the atoms of isomorphous substances are not only the same in form, but equal in dimensions. It follows, therefore, that any one of the preceding metals might be substituted for any other in the respective protoxides, and on that account, according to the modern theory, they are the chemical equivalents of each other, for that expression is used now in a different sense from what it formerly had. Chemical equivalency between two or more substances consists in their capacity for being exchanged one for the other. Direct or indirect substitution forms the basis of the modern doctrine of chemical equivalents.

Substances which are capable of replacing one another in compounds, and which are endowed with qualities mutually analogous, are said to be isomeric. Many isomeric compounds are formed of the same materials, in the same proportions, and yet differ essentially both in their physical and chemical properties; whence M. Daniel observes, that a specific and definite arrangement of the constituent molecules in space appears to be no less essential to the individual constitution of bodies than a certain proportion between their heterogeneous ingredients.

Successive substitution in isomeric bodies does not alter the character of the chemical formulæ of these bodies; thus chlorine, bromine and iodine, are chemically equivalent with an atom of hydrogen, for they may be put for one or more atoms of hydrogen in various compounds without changing the character of the chemical formulæ of these compounds. The peroxide of hydrogen consists of one atom of hydrogen and two of oxygen; hence if 32·5 parts of zinc, 28 of manganese, and 32 of copper be successively put for the atom of hydrogen, the result will be the peroxides of zinc, manganese and copper respectively. Here the character of the chemical formula of the original compound remains the same, and the three metals are chemically equivalent to one another, and to the atom of hydrogen. In many compounds organic and inorganic, one or more atoms of hydrogen may be replaced by an equal number of atoms of sodium, potassium, zinc, &c., without altering the character of the chemical formula of the compound.

Olefiant gas, olefiant oil and paraffin, form an isomeric series of a gas, a liquid and a solid, consisting of carbon and hydrogen. The gas contains 86 parts in 100 of carbon, and forms the most luminous part of coal gas.

M. Dumas has proved it to be a general law, that when three isomeric bodies are arranged in the sequence of their chemical properties, there will also be a sequence in their respective atomic numbers, and that whenever this symmetry of chemical properties and atomic weights obtains, any one of these substances may be substituted for the other without changing the chemical character of the formula.

Sulphur, selenium, and tellurium, form an isomeric group; that is, they form a sequence, with analogous qualities, for sulphur is the most volatile; selenium, a simple substance found in iron pyrites in Sweden, is less volatile; and tellurium is the least volatile and with regard to their atomic sequence, the atomic weight of sulphur is 16, that of tellurium is 64, and half the sum of these numbers is 40, the atomic weight of selenium, the mean term. Hence selenium might be put in any compound for the sulphur, and the tellurium for the selenium, without changing the chemical character of its formula.

The metallic group of calcium, strontium, and barium, are endowed with analogous properties, perfect harmony in their chemical qualities, and in the numbers expressing their atomic weights. That of calcium is 20, that of barium is 68, and the half sum is 44, the atomic weight of strontium. So calcium might be put for strontium, and strontium for barium, in any compound without altering the character of its formula. Professors Johnson and Allen have shown that the new metalloids cæsium and rubidium form an isomeric triad with potassium, for the atomic weight of cæsium is 133, that of rubidium 86, and that of potassium 39.

Transmutations of one isomeric substance for another may also be made in organic bodies, but chlorine, bromine, and iodine form an exception to M. Dumas’s law, because the arithmetical relation is wanting.

There are certain groups of substances, especially among the metals, whose atomic weights are in regular arithmetical series, as those of titanium, tin, and tantalum, which are 25, 59, and 92, the common difference being 34.

Certain groups of combined atoms called compound radicles are much more important than the preceding. They unite chemically with one another, and with other substances in definite proportions, precisely as if they were ultimate atoms. They are even capable of being substituted one for the other, forming groups of infinitely varied properties, and thus chemical equivalency extends to them.

Cyanogen, amidogen, and the peroxide of hydrogen are compound radicles which combine with other substances and with simple atoms as if they themselves were simple elements; though the first is a chemical compound of two atoms of carbon and one of nitrogen, the second a chemical compound of one atom of nitrogen and two of hydrogen, and the peroxide contains as before mentioned two atoms of oxygen and one of hydrogen. All three are capable of replacing hydrogen, chlorine, and metals by equivalent substitutions. For example, the chlorate of potash consists of one atom of potash, an atom of chlorine, and five atoms of oxygen; if then an atom of cyanogen whose weight is 26, be put for the atom of chlorine, the result would be the cyanate of potash.

Cyanogen, formed by passing nitrogen over red-hot carbon, consists of two equivalents of carbon and one of nitrogen. It is a frequent constituent of organic and inorganic compounds, and travels in the voltaic circuit as if it were a simple substance.

Ammonia consists of three equivalents of hydrogen and one of nitrogen; now, when the radical phenyle, which consists of twelve equivalents of carbon and five of hydrogen, is put in the ammonia for one equivalent of hydrogen, the result is aniline, whence most of the coal tar colours are obtained. In like manner carbazotic acid, a beautiful yellow dye from coal tar, is carbolic acid, three of whose equivalents of hydrogen have been replaced by three equivalents of an oxide of nitrogen.

Compound radicles, consisting of carbon and the three elementary gases, have been discovered which enter into combination in definite proportions as simple atoms, and all compound radicles travel in the galvanic circuit as equivalents to the elementary substances. Hitherto they have been regarded as representatives or equivalents of one atom of hydrogen. Now it is generally admitted that each has the property of replacing two, three, or more atoms of hydrogen by equivalent substitution. This multiple equivalency among compound radicals forms the basis of what is called the polyatomic theory, now so much employed by MM. Hofmann, Berthelot, and other great modern chemists.

Water is the most common radicle both in the inorganic and organic world. Though a compound of oxygen and hydrogen, it enters, according to the law of definite proportion, into the composition of various amorphous bodies in a dry state, that is in the form and proportion of its gases. It is an essential element in the greater number of crystals, and abounds in organic matter. In certain cases the same substance crystallizes at different temperatures, unites with different quantities of water under the form of oxygen and hydrogen, and assumes corresponding forms. For example, the seleniate of zinc unites with three different portions of water and takes three different forms, according as its temperature is hot, lukewarm, or cold. Thus each particle of water, containing one atom of oxygen and one of hydrogen, combines with one atom of zinc in three different proportions as if it were a simple atom.

The water of crystallization may be driven off from many substances by heat, as from the hydrates of lime, iron, copper, &c., but when combined with the oxides of certain metals, potassium for instance, it cannot be driven off by any means whatever. In general a heat of 212° Fahr. is sufficient, but some crystals lose their water of crystallization at the ordinary atmospheric temperature.

Crystals whose atoms are in unstable equilibrium, are readily altered both externally and internally by a very moderate degree of heat. Arragonite and calcareous spar are isomeric, that is, they are chemically the same but differ in form and hardness, which shows that their molecules are grouped differently. When the arragonite is heated, the inertia of its atoms is overcome, the crystal explodes with force, and becomes a mass of crystals of calcareous spar. The expansive force of the heat suddenly overcoming the force of cohesion causes the explosion, and at the same time disturbs the unstable repose of the atoms, which immediately obey their natural attractions and assume the stable form of calcareous spar.

Dialysis is a method of separating and analysing substances by means of their diffusion in alcohol or water. If a wide-mouthed vial nearly full of a solution of common salt be placed in a jar of water, after a few days it will be found that the particles of salt have come out of the vial and have diffused themselves through the superincumbent water, even to its surface. Now Professor Graham, Master of the Mint, with whom this subject originated, made three arrangements precisely like that described; the three vials were exactly similar and equal, the three jars exactly the same in size and form, and contained the same quantity of water; but the first vial contained a solution of gum arabic, the second a solution of Epsom salt, and the third a solution of common salt. After fourteen days the diffusion of the gum had risen through one half of the superincumbent water, while the particles of both the salts had risen to the surface. However the common salt would have risen much higher, for when the strata of water at the two surfaces were drawn off by a siphon and evaporated to dryness, there was fifteen times as much common salt as Epsom salt. The three solutions are heavier than water, yet they rise notwithstanding their gravitation, whence Mr. Graham thinks that there is probably an attraction between the particles of the dissolved substances and those of the water. The force of molecular attraction is more powerful than gravitation, hence the particles must rise by the difference of the two forces.

After many comparative experiments the professor concluded that most substances differ in diffusibility, and that crystalloids or crystalline substances such as salts, sugars, &c., are much more diffusible than colloids or amorphous sticky bodies, such as gum, caramel, jellies, and substances that combine with the hydrogen of the water to form gelatinous hydrates.

The partial decomposition of definite chemical compounds may be effected by diffusion. Alum, which is a double sulphate of the two metals potassium and aluminium, furnishes an example; when allowed to diffuse itself from its aqueous solution, the diffusive tendency of potassium compounds is so much greater than the diffusive property of aluminium compounds, that a portion of the sulphate of potassium actually breaks away from the sulphate of aluminium with which it was combined, in order to diffuse itself in the superincumbent external water more freely than the sulphate of alumina can do.

Common salt diffuses itself in a solid mass of jelly almost as easily and extensively as in the same bulk of free water. Thus colloid bodies do not interfere with the diffusion of crystalloids such as salts, but they almost entirely arrest the diffusion of one another. Solutions of salts, sugars, and other crystalloids pass freely through colloid substances, such as parchment-paper, vellum, and membrane into water, although they have no pores, because the particles of the crystals unite diffusively with the water combined in these substances, which solutions of gum, caramel, and other colloids cannot do. These colloid substances are permeable to solutions of crystalloids, impermeable to solutions of colloids. This constitutes Dialysis.

The instrument used by Mr. Graham was a little tray formed of vellum or membrane stretched tightly over a hoop of gutta-percha and capable of holding a liquid and floating on water. When a mixed solution of equal parts of salt and gum is put into the tray, after a time all the salt will have passed into the water below, leaving nothing in the tray but an aqueous solution of gum.

The following is one of the most extraordinary results of dialysis. Mr. Graham took a silicate of soda, a soluble crystalline salt formed by fusing quartz with carbonate of soda at a red heat, which diffuses readily. He acidulated the aqueous solution of the salt with hydrochloric acid, which changes the constituent silica from being a crystalloid substance into a colloid form. When the liquid was poured into the tray floating on water, after four days, the whole of the acid and the chloride of sodium had been diffused in the water and nothing remained in the tray but an aqueous solution of quartz. There remained in fact, a solution of sand in water, a substance so hard that no pure aqueous solution of it had ever been obtained. Many other crystalline substances besides quartz can exist both in the colloid and crystalloid states.

All colloid substances are characterized by non-crystalline habits, low diffusibility, chemical inertness, high atomic weight, and above all by their mutability. The aqueous solution of quartz is limpid and liquid, even if it contains 14 per cent. of silica, but after a time it becomes opalescent, viscous, and ultimately sets into a firm insoluble jelly, capable however of solution by chemical means. This jelly gradually shrinks, exudes pure water, and when perfectly dry it forms a glassy, transparent, but not anhydrous substance, and the residue left by ignition has a specific gravity of 2·2, that of crystallized silica being 2·6.

Mr. Graham has obtained many pure aqueous solutions of organic and inorganic matter, most of them being unstable. Ice near or at its melting point is believed to be a colloid body, consequently it is unstable and resembles a firm jelly, having a tendency to rend and recombine. ‘The constant intervention of colloid septa in so many of the phenomena of animal and vegetable life gives to the subject of dialysis a high physiological interest, and it will doubtless exercise an important influence on the progress of physiological research.’^[12]

Subsequently to these researches Mr. Graham published a memoir on a new method of analysing gases which he had called atmolysis. The memoir may be regarded as consisting of four parts, the first of which is preliminary, being on the reciprocal diffusion of gases through porous plates. The next three parts relate to effusion, or the passage of gases under constant pressure through a minute opening in a very thin plate into a vacuum; transpiration, or the passage of gases through capillary tubes into vacuo; and lastly atmolysis, which is the partial separation of a mixture of gases and vapours of different degrees of diffusibility by permitting them to diffuse themselves through a porous plate into a vacuum: a new kind of analysis, which possesses a practical character of extensive application.

The diffusing instrument employed by Mr. Graham was a cylindrical glass tube about an inch in diameter, ten inches long, with one end closed by a very thin porous disc of compressed artificial graphite fixed by a resinous cement. While the tube was being filled with hydrogen gas over a trough of mercury, the escape of the gas was prevented by covering the graphite very carefully with a thin sheet of gutta percha. As soon as the gutta percha was removed, the reciprocal diffusion of the gases began, and in from forty to sixty minutes the whole of the hydrogen had escaped from the tube, and a quantity of atmospheric air amounting to about one fourth of the volume of hydrogen had entered the tube and taken its place, according to the ordinary law of the diffusion of gases. During this time the mercury rises in the tube so as to form a column several inches high, a fact which is a striking demonstration of the intensity of the force with which the reciprocal penetration of different gases effected.

Natural plumbago or graphite has little or no porosity and cannot be used in these experiments, but the pores of artificial graphite of which pencils are made, appear to be so minute that only isolated molecules of gas are able to pass, without however being at all impeded by friction; for the smallest pores that we can suppose to exist in the graphite must be real tunnels compared with the minuteness of the ultimate atoms or molecules of a gaseous body. The cause of motion appears to reside solely in that internal movement of molecules which is now generally admitted as an essential condition of matter in a gaseous state. The molecules and atoms are assumed to be perfectly elastic and to move in all directions with different velocities according to the nature of the gas. Enclosed in a porous vessel the moving atoms constantly strike against its walls and against one another, but in consequence of their perfect elasticity, no loss of movement results from the collision. When the gases inside and outside of the tube are of the same density and molecular movement, an exchange takes place without any perceptible change of volume; but when the two gases are of different densities and molecular velocities, then the reciprocal penetration ceases to be equal on the two sides. Reciprocal diffusion of gases is accelerated by heat and retarded by cold; the tension of the gases is increased in the first case, and diminished in the second.

In Mr. Graham’s experiments relating to effusion, a gas under a constant pressure was on one side of a minute opening in a very thin plate, and a vacuum on the other. The rapidity with which air or gases enter the vacuum depends upon their specific gravity. A gas rushes into a vacuum with the speed acquired by a heavy body in falling from the height of an atmosphere of the gas in question supposed to be everywhere of the same density. The height of this uniform atmosphere will be in an inverse ratio to the density of the gas. An atmosphere of hydrogen, for example, will be 16 times higher than one of oxygen. But the velocity acquired by a heavy body not being in direct proportion to the height, but to the square root of the height, it follows that the rate of flow of different gases into a vacuum will be in an inverse ratio to the square root of their respective densities. The rate of flow of oxygen being represented by 1, that of hydrogen will be represented by 4 the square root of 16. This law has been verified by experiment, and is quite analogous to that which regulates molecular diffusion, but the phenomena are essentially different. It is the gas en masse which partakes of the movements of effusion, whilst only the molecules or atoms of a gas are affected by the movements of diffusion. For that reason the swiftness of the effusion of a gas is many thousand times greater than that of diffusion. The swiftness of the efflux of atmospheric air is as rapid as the velocity of sound.

The rate of the flow of different gases under constant pressure through capillary tubes into a vacuum, constitutes the capillary transpiration of gases. These rates bear a constant proportion to one another, but they are singularly unlike the rates of effusion. They are independent of the material of the tube; they are not governed by specific gravity; and ‘they appear to be in constant relation with no other known property of the same gases; and they form a class of phenomena remarkably isolated from all else at present known of gases.’

The pores of graphite are so fine that it is incapable either of effusion or transpiration, but it is readily penetrated by means of the molecular or diffusive movements of gases, as appears on comparing the time requisite for the passage of equal volumes of different gases under constant pressure into a vacuum. For oxygen, hydrogen and carbonic acid gas, the times are nearly as the square roots of their densities.

The atmolysis or partial separation of mixed gases and vapours of unequal diffusibility, can be effected by allowing the mixture to penetrate through a graphite plate into a vacuum. The amount of separation is in proportion to the pressure, and attains its maximum when the gases pass into a perfect vacuum. One of the results of atmolysis was the concentration of oxygen in atmospheric air. When a portion of air confined in a vessel was allowed to penetrate into a vacuum through graphite or unglazed earthenware, the nitrogen passed more rapidly than the oxygen in the ratio of 1·0668 to 1, and the portion of oxygen is proportionally increased in the air left behind in the vessel. The increase of oxygen actually observed when the air in the vessel was reduced from 1 volume to 0·5 was 0·48 per cent. The diffusion was continued till the air in the vessel was reduced to 0·0625 and the concentration of the oxygen in it amounted to 2·02 per cent. The molecular or diffusive mobility exercises a certain influence on the heating of gases by contact with heated liquid or solid substances. The more rapid the molecular movement of a gas is, the more frequent will be the contact of the molecules and the quicker will be the communication of heat. The greater cooling power of hydrogen compared with that of oxygen or air is probably owing to that cause. ‘Oxygen and hydrogen gas have the same specific heat for equal volumes; but a hot object placed in hydrogen is really touched 3·8 times more frequently than it would be if placed in oxygen gas. Dalton had already ascribed this peculiarity of hydrogen to the high mobility of the gas.’^[13]

It appears that isomorphic substances such as chloride, bromide, and iodide of sodium, have a similar diffusibility, another of the many analogies between these singular marine substances.

Modem chemistry is essentially experimental; the unprecedented magnitude to which British manufactures have risen is chiefly owing to experiments conducted with consummate skill and dexterity. In these investigations, accidental circumstances have sometimes occurred which led to other researches quite different from that originally in view, which have had unexpected and invaluable results. Although the simple elements are few, they are capable of an infinite variety of combinations, so that by analysis and new combinations, the most useful and valuable materials are now obtained from obnoxious or useless substances, formerly thrown away. The instances are numerous; but sawdust may be mentioned as one of the most remarkable. It was not even fit for fuel, but now oxalic acid, a bleaching principle most extensively used in the various processes of calico printing, is procured from it; the quantity required may be imagined, since the cotton cloth annually printed in Great Britain previous to the American war, would surround the earth’s equator nineteen times. Oxalic acid, which is a vegetable substance, found combined with potash in wood sorrel or Oxalis acetosella, used to be made from sugar or starch, by the action of nitric acid. Now starch, sugar, and woody fibre or fibrine, all contain twelve parts of carbon and different portions of oxygen and hydrogen, always in the proportions that form water; hence the name of carbohydrates. Their composition is so similar that the one may be changed into the other by the addition or subtraction of one or two atoms of water under its atomic form; thus when fruits ripen, the starch they contain is changed into sugar by the addition of one atom of water under its dry form.

Now sawdust is woody fibre, and might be changed by nitric acid into oxalic acid like the others. But a less expensive method is actually employed.

When sawdust, mixed with two equivalents of the hydrate of soda and one equivalent of the hydrate of potash, is exposed to a heat of 400° for a few hours, the substances are fused, and when raised to a still higher temperature the hydrates are decomposed: hydrogen is evolved, and the carbon combines with the oxygen to form the oxalate of soda and the oxalate of potash. In order to separate these oxalates they are put into a filter, a solution of carbonate of soda is passed through it; the oxalate of soda remains in the filter, the carbonate of potash passes through it; and when lime is added to the oxalate of soda, the soda is liberated, passes through the filter, and the oxalate of lime remains. Sulphuric acid is then added to the oxalate of lime, sulphate of lime is formed, and oxalic acid mixed with water remains, and by evaporation forms into beautiful crystals of oxalic acid. This is an instance of a complicated chemical process; nevertheless it is carried on to a vast extent in Manchester, nine tons a week being furnished by one manufactory alone. Two pounds of sawdust yield one pound of oxalic acid.

In ordinary distillation a volatile substance such as water, by absorbing the heat applied to it, becomes converted into vapour; by abstracting the absorbed heat from the vapour, it is reconverted into the original substance. Destructive distillation, on the contrary, consists of an entire destruction of the original substance and a simultaneous production of new substances. Of this the destructive distillation of coal furnishes the most interesting illustration, and shows at the same time the success of modern chemistry in utilizing waste substances.

Coal had been distilled for years to furnish gas for the illumination of our cities before it was discovered that the refuse contained principles of the greatest value. The products of the distillation are threefold: gas, coal water, and coal tar.

Coal gas is a combination of various gases, whose illuminating properties depend upon, and are exactly in proportion to, the quantity of carbon they contain. The particles of carbon raised to a white heat give the light, for the gaseous part has a feeble flame, and requires a higher temperature than solid matter, which becomes luminous at about 700° in the dark, and at from 1000° to 2000° in bright daylight. Coal gas consists of a combination of illuminants: olefiant gas, which contains 86 per cent. of carbon, carburetted hydrogen or marsh gas, which contains 75 per cent., carbonic oxide, carbonic acid gas, hydrogen, sulphuretted hydrogen, and a very small quantity of nitrogen, besides the bisulphide of carbon, and benzol, a pure hydro-carbon, consisting of 12 equivalents of carbon and 6 of hydrogen.

The poisonous quality of coal gas is owing to the carbonic oxide, which is fatal to life, and its explosive quality to carburetted hydrogen, which also is generated by decomposition of vegetable matter in stagnant pools and marshes; and in the firedamp of mines it still bears testimony to the vegetable origin of coal. That fatal gas increases in explosive force as it mixes with atmospheric air, and is at a maximum when it amounts to 12 per cent. Hydrogen, carburetted hydrogen, and carbonic oxide do not add much to the light, on account of the feeble flame of hydrogen and the small quantity of carbon they contain, but they force the chief illuminating gases out of the iron retorts in which the coal is distilled before the heat has had time to decompose them, and they also enable them to burn without smell or smoke.

Carbonic acid, bisulphide of carbon, and sulphuretted hydrogen are impurities from which coal gas is freed before it is fit for use. By passing the gas over lime, the lime absorbs both the carbonic acid and the sulphuretted hydrogen; one per cent. of carbonic acid diminishes the illuminating power six per cent., and the sulphuretted hydrogen has an abominable smell.

The bisulphide of carbon, consisting of one equivalent of carbon and two of sulphur, is got rid of by passing the gas over hot lime. The water of the lime is decomposed, and carbonic oxide and sulphuretted hydrogen are produced; but the latter may be absorbed by passing the gas again over lime, or through a mixture of sawdust and the oxide of iron. The oxide of iron decomposes the sulphuretted hydrogen, forms water and sulphide of iron, then the air restores the sulphide to oxide, and the sulphur is deposited in the mixture. After passing the gas through it till none of that impurity remains, the gas is fit for use. The test is the nitro-prusside of sodium, which the gas stains purple if any of the impurity remains.

Paraffin, already mentioned as isomeric, is a pure hydrocarbon, colourless, transparent, and of crystalline texture. It melts at a heat of 120° or 130°, burns like wax without smell or smoke, and makes beautiful candles, which give a brilliant light on account of the 86 per cent. of carbon they contain. Paraffin oil is much used for lamps; the manufacture of these two substances at Bathgate is one of the largest chemical establishments in the world.

The black fœtid gas water resulting from the distillation of coals, formerly thrown away, is so rich in the salts of ammonia, that it has become the chief source from which these materials so important in the arts are obtained.

Ammonia is well known to be a colourless gas, with an acrid pungent smell, consisting of one equivalent of nitrogen and three of hydrogen. It has an alkaline character, combining with acids, and is extremely soluble in water.

Now the gas water contains carbonate of ammonia and sulphide of ammonium, and when any acid strong enough to decompose these substances is put into the liquid, the carbonic acid and sulphuretted hydrogen being volatile are driven off, and the acid combines with the ammonia to form a salt. For example, when muriatic acid is put into the liquid, it drives off the volatile gases and combines with the ammonia in solution to form muriate of ammonia, which is dissolved in water and evaporated till it crystallises; then it is vaporized and sublimed to free it from impurities.

When ammonia and muriatic acid are separately vaporized, the two colourless transparent vapours, when mixed, combine into solid muriate of ammonia, a result so unexpected that as Mr. Playfair justly observes, it could only have been taught by experiment. About 4,000 tons of muriate of ammonia are annually made from gas water in England for soldering, and for making alum.

Sulphate of ammonia to the extent of 5,000 tons is annually made by adding oil of vitriol to the liquid. It is also used for making alum, as well as for manure; it supplies our grain with nitrogen, an important article of vegetable food. To these may be added 2,000 tons of carbonate of ammonia, so that a substance that was considered to be good for nothing yields 11,000 tons of valuable materials, but even this quantity forms only part of the enormous amount annually consumed in the manufactures of Great Britain.

Coal tar is of complicated nature, containing a variety of substances, many of which are more or less volatile. When it is distilled by sending a current of steam through it, the steam collects the volatile parts, condenses them into naphtha; the first product is condensed steam or water with naphtha swimming on its surface, the next product is dead oil, and the remainder is pitch.

By the aid of the crude naphtha thus produced, Indian rubber is dissolved and waterproof clothes are made. When purified by sulphuric acid, it forms a substance like tar which is thrown away, and the remaining products when clarified are acid oils and neutral hydro-carbons. The carbolic and cressylic acids are the most important of these acid oils. The carbolic acid, which has the property of arresting the putrefaction and decay of organic matter, consists of 12 equivalents of carbon, 6 of hydrogen, and 2 of oxygen. The cressylic acid only differs from the preceding by having two more equivalents of hydrogen and two of oxygen in its chemical composition.

Creosote is a mixture of these two acids. Those vast beams of wood that are driven as piles into the sand or mud at the bottom of the sea, as well as the timbers that form marine superstructures, are saturated with it to a certain depth to preserve them from the attacks of marine insects, especially Limnoria terebrans, an isopod crustacean, which is so destructive in some of our harbours. The wood is deprived of its air by heat and the creosote easily enters.

Carbolic acid is liquid, but becomes solid when purified and dried; and as already mentioned the brilliant yellow dye, carbazotic acid, one of the coal tar colours, is a compound radical, in which the peroxide of nitrogen has replaced three equivalents of hydrogen. The other coal tar colours are obtained from the neutral hydro-carbons, that is to say, compounds of hydrogen and carbon, such as benzol, toluol, and other analogous substances.

Benzol, which consists of 12 equivalents of carbon and 6 of hydrogen, is very volatile, boiling at 117° Fahr., and when acted upon by nitric acid, it forms a compound radicle in which one equivalent of oxide of nitrogen takes the place of one of hydrogen. It smells strongly of bitter almonds, and may be used with safety instead of them. When water and iron are mixed with nitro-benzol, the iron combines with the oxygen and forms oxide of iron, and the result is rusted iron and aniline, which is the origin and foundation of the coal tar colours. Now aniline consists of 12 equivalents of carbon, 7 of hydrogen, and 1 of nitrogen. It is a compound radical: it is ammonia in which one equivalent of hydrogen has been replaced by the radical phenyle, consisting of 12 equivalents of carbon and 5 of hydrogen. It may be remarked that in all these chemical operations the quantity of carbon has remained the same.

Aniline is a colourless liquid, and, being an analogue of ammonia, it readily combines with the different acids to form the beautiful coal tar dyes, for which the world is indebted to the brilliant researches of Dr. Hofmann, professor of chemistry.

By combining a solution of the chloride of lime with the colourless liquid aniline, he obtained the beautiful colour mauve, but it could not be used as a dye till it was rendered permanent by his pupil, Mr. Perkins. His next discovery was the rich crimson crystalline dye magenta, which M. Verguin first introduced into trade at Lyons as a dyeing agent. It may be produced by mixing the anhydrous bichloride of tin with aniline and then driving off the excess of aniline by heat. Other metallic chlorides, nitrates, and many oxidizing agents, have the power of converting aniline into magenta; as for example when the two colourless liquids acetic acid and aniline are mixed and heated, a chemical combination takes place in which three atoms of ammonia have coalesced into one, a salt is formed which is the acetate of aniline or magenta. Here two liquids unite to form a solid and as in many other instances the resulting substance has the power of decomposing light which neither of its constituents can do. Magenta has a redder tint than mauve, and on that account it is sometimes called aniline red. Professor Hofmann has discovered quite recently that pure aniline has not the property of producing these colours, but that they originate in an impurity of the aniline called toluidine.

Rosaniline or roseine, a white substance, is the base of aniline. It is a powerful alkali, readily combining with acids to form highly coloured salts, many of which have a tendency to crystallize, like magenta. This base is most easily extracted from the acetate of aniline. The boiling solution of that salt decomposed by a large excess of ammonia, yields a crystalline precipitate of a reddish colour, and when the colourless liquid is separated by filtration from the precipitate, it deposits on cooling perfectly white needles and tablets of pure rosaniline. This substance unites to acids in three different proportions forming three kinds of salts. The salts that contain one equivalent of acid are extremely stable compounds; for the most part they have a green metallic reflection like some insects’ wings; by transmitted light they are red, and their solutions in alcohol have the magnificent crimson colour of magenta.

A bright purple dye is furnished by mixing equal weights of magenta and aniline. When this mixture is kept at the temperature of 329° for some hours and then mixed with water and hydrochloric acid to remove any excess of magenta or aniline, the result is an insoluble purple residuum or precipitate, but which when well washed with water becomes soluble in alcohol and boiling water slightly acidulated with acetic acid. When the insoluble purple residue is boiled several times with dilute hydrochloric acid, a fine blue dye is formed; azuline, the most beautiful of the blue dyes, which resists the action of the strongest acids, and which is produced by oxidizing aniline under high pressure. It was first prepared at Lyons from phenic acid, a product of the distillation of coal; when pure it appears under the form of copper bronze-coloured crystals soluble in alcohol, to which they communicate a magnificent blue colour tinged with red; but most of the blue dyes are derived from carbolic acid and from creosote. A blood-red colour is the direct result of mixing the muriatic and phenic acids. Aniline, the great source of the coal tar colours, yields also a fine yellow. A vast deal of talent has been employed in the research of colouring dyes both at home and abroad, in which the manufacturers themselves have shown great scientific knowledge.

Attempts have been unsuccessfully made to obtain a green dye from chlorophyll, the green colouring matter of plants. The want was for a short time supplied by Lo-hao, a Chinese dye, but being unstable it was given up. However the very same substance has been procured from the Rhamnus cathartica (Buckthorn), one of the commonest European trees. M. Charwin of Lyons, who made the discovery, has utilized a waste substance, and rendered it permanent as a dye. It is the only known substance which with proper reagents is capable of producing all the seven colours of the spectrum.^[14]

The coal tar colours have nearly superseded those from lichens which incrust rocks, walls and stems of aged trees with brilliant colours, which do not however furnish dyes directly; they yield a colourless crystalline substance which combines with alkalies to furnish very beautiful dyes; it is exactly the opposite of rosaniline, which is a base. The Variolaria dealbata yields litmus or orchil, from which the beautiful French purple is made. The Rocella tinctoria and fusiformis give blue and purple, and the pale yellow lichen, Parmelia parcolerina furnishes a bright yellow dye, which a little ammonia changes to a rich red, inclining to purple. Mauve was first made from orchil, but was not permanent. The fine dyes, alizarine blue, Turkey red and garancine, are still much in use. They are derived from madder, the dried roots of the Rubia tinctorum; the madder dyes most extensively employed are alizarine and flower of madder. Mauve and other dyes are derived from guano, the offal of seabirds, which is imported in large quantities for manure.

The coal tar colours are manufactured on a highly scientific plan and most extensive scale in Great Britain, to supply the enormous quantity annually consumed in dyeing silk and printing cotton. In general, animal substances such as silk and wool can be permanently dyed at once, because they have a strong affinity or attraction for coloured dyes. If silk is destined to be a moiré, the silk before it is woven undergoes a chemical process in order to introduce fatty matter into it which gives a softness to the silk when woven and renders it fit to receive the moiré by intense pressure.

Cotton cloth has no affinity for dyes, which are washed out at once if not fixed by art, because cotton fibre consists of minute tubes generally open at the extremity, which imbibe the dye by capillary attraction, but cannot retain it unless fixed by a mordant, such as the white of a raw egg, which readily absorbs any dye that is mixed with it, and being then laid on the cloth in any pattern it is absorbed by the tubular fibres, and when coagulated by steam or any other application of heat it is immovably fixed. Both animal and vegetable substances afford a variety of mordants. Caseine or cheese, the curd of milk, which may also be obtained from pease and beans, is the mordant most used by calico printers; for if caseine be dissolved in twice the quantity of alkali necessary for its solution, it coagulates like white of egg and may be used in the same manner. Skimmed milk cheese from Scotland and Holland when purified is extensively used in calico printing. The quantity of mordants required is very great, for of all the cotton that was imported into Britain before the late American civil war, one seventh only was manufactured into muslin and printed calico, yet as already mentioned that was sufficient to envelope the earth’s equator nineteen times, and twenty-seven millions of pieces were exported annually. Atmospheric electricity and ozone affect the process of dyeing, and east wind has a retarding and injurious effect. The Lyons manufacturers, not less celebrated for their scientific skill and taste than for the brilliancy of the colours, have an advantage in their fine climate and bright sun.

It is a singular circumstance that petroleum has existed in enormous quantities throughout the North American States and a great part of Canada, unnoticed and neglected till the year 1859, when its value was discovered, and it almost immediately formed a new and extensive branch of commerce, for during the succeeding year at least 1,000 wells were dug, some of which enriched the proprietors; others were a failure.

Petroleum from the fountains of Is, on the banks of the Euphrates about 120 miles from Babylon, furnished the asphaltic mortar for building Nineveh 2,000 years before the Christian era. There are many sources of naphtha, petroleum, and asphalt in Europe and Asia, which like those in Trinidad and Venezuela occur for the most part in rocks of the newer, secondary and tertiary formations, though sometimes in the lower. But in the northern part of the United States and Canada these substances occur in rocks of all ages from the lower silurian to the tertiary period inclusive; they are usually found in the limestones and more rarely in the sandstones and shales. Petroleum collects in the fissures of the rocks, chiefly in those that have a tendency downwards; in wells dug for it near one another, an abundant supply is furnished at all depths from 70 to 300 feet. In some parts of Ohio and Canada the ground is saturated with petroleum, so that it is believed there is enough in North America to supply the world for ages. In 1861 no less than 42,000,000 gallons of petroleum were sent to England. The wells are not without danger, for when they pass through the coal strata, the petroleum is accompanied by a highly inflammable gas which on one occasion was accidentally set on fire; it ignited the petroleum, which was forced out as from the mouth of a volcano, and covered the ground with liquid fire far around; at the same time the burning gas formed an incandescent atmosphere which extended to a still greater distance.

The distillation of petroleum yields substances for the most part identical with those arising from the distillation of coal. The crude petroleum is put into an iron retort connected with a coil of iron pipes surrounded by cold water, called the condenser. Heat is applied to the retort, and from the open extremity of the condenser, a pale coloured liquid with a strong smell flows, which is very volatile and explosive naphtha. After the naphtha has passed over, an oil of excellent illuminating quality is distilled over. Steam is then forced into the retort, and a heavy oil is driven over, and there remains a black, oily, tarry matter, and a black cake used for fuel. After the naphtha has been repeatedly distilled, benzol is formed, and when the heavy oil is cooled to 30° Fahr., crystals of paraffin appear, which are separated from the oil by pressure, and when they are purified by alternate pressure and agitation in a melted state, they are moulded into candles. This paraffin is identical with that from coal. Among the products of the distillation of petroleum are naphthalin whence aniline is obtained, which yields mauve, magenta, and the other coal tar colours, also solferino which yields dianthine and other dyes and has been proposed as a substitute for chloroform and ether. Many other substances have been separated from petroleum which like some from coal have not yet been chemically examined. Most of the substances obtained from petroleum and the distillation of coal are common also to distilled peat, and now it is proposed to utilize sea weeds, in which the northern coasts of Scotland and Ireland are so rich. They were burnt for many years chiefly to furnish soda, but as that substance is obtained at a cheaper rate from salt, kelp or sea weed ashes has only been made lately to obtain iodine for medical purposes, and more than one half is wasted in the process. Besides iodine and six other substances generally procured from kelp, Mr. Stanford has discovered that it contains naphtha, paraffin oil and volatile oil rich in benzol, which yields aniline and magenta dyes and shows that marine vegetation as well as terrestrial abounds in colouring matter.

Every substance is now of use, no substance is without its value, but it would be a vain attempt to mention the innumerable discoveries made by experimental chemistry, which is daily extending its empire over the three kingdoms of organic and inorganic nature.