PART III.

Of OPERATIONS on ANIMAL SUBSTANCES.

CHAP. I.

Of Milk.

PROCESS I.

OBSERVATIONS.

The milk of animals, that feed only on vegetables, is of all animal matters the least removed from the vegetable nature. The truth of this will be demonstrated by the experiments we shall produce by and by, for the further analysis of milk. For this reason we judged, with Mr. Boerhaave, that it was proper to begin the analysis of animals by examining this liquor.

Most Chymists justly consider Milk as of the same nature with Chyle. Indeed there is great reason to think, that, except some small differences to be afterwards taken notice of, these two matters are nearly the same. They are both of a dead white colour, like that of an emulsion; which proves that, like emulsions, they consist of an oily matter divided, diffused, and suspended, but not perfectly dissolved, in an aqueous liquor.

It is not surprising that these liquors should resemble emulsions; for they are produced in the same manner, and may very justly be called Animal Emulsions. For how are vegetable substances converted into Chyle and Milk in an animal body? They are bruised, divided, and triturated by mastication and digestion, as perfectly, at least, as the matters pounded in a mortar to make an emulsion; and must thereby undergo the same changes as those matters; that is, their oily parts, being attenuated by those motions, must be mixed with and lodged between the aqueous parts, but not dissolved therein; because they do not, in the bodies of animals, meet with saline matters, sufficiently disentangled and active, to unite intimately with them, and by that means render them soluble in water.

Nevertheless Chyle and Milk, though produced in the same manner as emulsions, and very much resembling them, differ greatly from them in some respects; owing chiefly to the time they remain in the bodies of animals, their being heated while there, the elaborations they undergo therein, and the animal juices commixed with them.

New Milk hath a mild agreeable taste, without any saline pungency; nor hath any Chymical trial discovered in it either an Acid or an Alkali. Yet it is certain that the juices of plants, out of which milk is formed, contain many saline matters, and especially Acids: accordingly Milk also contains the same; but the Acids are so sheathed and combined, that they are not perceptible. The case is the same with all the other liquors intended to constitute part of an animal body: there is no perceptible Acid in any of them.

Hence it may be inferred that one of the principal changes which vegetables undergo, in order to their being converted into an animal substance, consists in this, that their Acids are combined, entangled, and sheathed in such a manner that they become imperceptible, and exert none of their properties.

Milk left to itself, without the help of distillation, or any additament whatever, undergoes a sort of decomposition. It runs into a kind of spontaneous analysis; which doth not indeed reduce it to its first principles, yet separates it into three distinct substances, as the process shews; namely, into Cream, or the buttery fat part, into Curd or Cheese, and into Serum or Whey: which shews that those three substances of which Milk consists, are only mixed and blended together, but not intimately united.

The first parts, being the lightest, rise gradually to the surface of the liquor as they separate from the rest: and this forms the Cream.

Cream, as skimmed from the surface of Milk, is not however the pure buttery or fat part; it is still mixed with many particles of Cheese and Whey, which must be separated in order to reduce it into Butter. The most simple, and at the same time the best method of effecting this, is daily practised by the country people. It consists in beating or churning the Cream, in a vessel contrived for that purpose, with the flat side of a circular piece of wood, in the center of which a staff is fixed. One would think that the motion, impressed on the Cream by this instrument, should rather serve to blend more intimately the particles of Butter, Cheese, and Whey, of which it consists, than to separate them from each other; as this motion seems perfectly adapted to divide and attenuate those particles. But, if we consider what passes on this occasion, we shall soon perceive that the motion by which Butter is churned is nothing like triture: for churning is no other, properly speaking, than a continually repeated compression, the effect whereof is to squeeze out from amongst the buttery particles those of Cheese and Whey mixed therewith; by which means the particles of Butter are brought into contact with each other, unite, and adhere together.

Milk, whether skimmed or no, grows sour of itself, and curdles in a few days. When it is newly curdled, the Cheese and Whey seem to be united, and to make but one mass: but these two matters separate spontaneously from each other, with the greatest ease, and in a very short time.

The acidity, which Milk naturally contracts in the space of a few days, must be considered as the effect of a fermenting motion, which discovers in that liquor an Acid that was not perceptible before. This, properly speaking, is an acetous fermentation, which Milk passes through in its way to putrefaction; and it soon follows, especially if the Milk be exposed to a hot air.

If, instead of leaving Milk to grow sour and curdle of itself, an Acid be mixed therewith, while it is yet sweet and newly milked, it immediately coagulates; which gives reason to think, that its curdling naturally is the effect of the Acid, which discovers itself therein as it grows stale.

The coagulation of Milk may also be considerably accelerated, by setting it in a sand-bath gently heated; or by mixing therewith a little of what, in the language of the Dairy, is called Runnet; which is nothing but some curdled and half-digested Milk taken from the stomach of a Calf: or both these methods may be employed at once, which will produce the effect still more expeditiously.

It is not difficult to find out the cause of these effects. The Runnet, which is Milk already curdled and grown sour, is an actual ferment to sweet Milk, disposing it to turn sour, much more readily: for though Milk, when thus hastily curdled by the Runnet, hath not a manifestly acid taste, yet it is certain that this Acid begins to exert itself. The proof thereof is, that, being exposed to the same degree of heat with Milk equally new, that is not mixed with this ferment, it turns sour much sooner. As to the effect of heat in coagulating Milk, there is nothing extraordinary in it: we know how much it promotes and accelerates all fermentative motion. The whole of this perfectly agrees with what we said before concerning fermentation.

Fixed Alkalis also coagulate Milk; but at the same time they separate the Whey from the Cheese, which floats on the liquor in clots. They give the Milk a russet-colour inclining to red; which may arise from their attacking the fat part.

The separation of Milk into Butter, Cheese, and Whey, is a kind of imperfect analysis thereof, or rather the beginning of one. In order to render it complete, we must examine each of these substances separately, and find the principles of which they consist. This we shall endeavour to do in the following process.

PROCESS II.

The analysis of Butter proves that this substance, which is an oily matter in a concrete form, owes its consistence to the Acid only, with which the oily part is combined: that is, it follows the general rule frequently mentioned above in treating of other oily compounds; the consistence whereof we shewed to be so much the firmer, the more Acid they contain. The first portions of Oil that come over in the distillation of Butter are fluid, because a pretty considerable quantity of Acid rose before them, which being mixed with the phlegm gives it the Acidity we took notice of.

This Oil, being freed from its Acid, and by that means rendered fluid, rises first; because it is by the same means rendered lighter. The kind of Butter that comes over afterwards, though it be fixed, is nevertheless far from having the same consistence as it had before distillation; because it loses much of its Acid in the operation. This Acid is what rises in the form of white vapours. These vapours are, at least, as pungent and irritating as the Sulphureous Acid or Volatile Alkalis: but their smell is different: it hath a resemblance, or rather is the same, with that which rises from Butter, when it is burnt and browned in an open vessel. But, when concentrated and collected in close vessels, as in the distillation of Butter, they are vastly stronger: they irritate the throat so as to inflame it; they are exceeding sharp and pungent to the smell, and are so hurtful to the eyes that they quickly inflame them, as in an ophthalmy, and make them shed abundance of tears. The great volatility of this Acid is entirely owing to a portion of the phlogiston of the Butter with which it is still combined.

It may be asked why Butter, or the oily part of Milk which hath the consistence of a fixed Oil, is more replete with an Acid than the Oils of the vegetables whereof the Milk was formed; as these Oils are almost all fluid, which indicates their containing less Acid before than after they were digested in the body of an animal. This must appear the more extraordinary, because the Acid contained in the liquors of animals is sheathed and imperceptible, and consequently incapable of combining with the Oils of vegetables so as to give them this consistence.

I think it will be easy to give a satisfactory answer to this question, if it be considered, that the Oils, which exist in the vegetable juices whereof the Milk is formed, are far from being combined with the whole Acid of those vegetables; because there is hardly a plant that doth not yield a great deal of Acid, even without the help of fire. Now, there is reason to think, that one of the principal effects of digestion is, to combine and unite this Acid, with the oily parts of vegetables, more intimately than it was before.

The further we advance in the analysis of animals, the more we shall be convinced, that, in the different elaborations, which vegetable substances undergo in order to their being changed into the nutritious juices of animals, nature employs all her powers to expel, destroy, or at least, weaken and blunt the Acids, so as to render them absolutely imperceptible. One of the best means by which she can effect this, is the combining and uniting them intimately with the oily parts: and this operation she probably begins in digestion. She gets rid of most part of the Acids contained in the aliments, by thus uniting them with the Oils contained in those aliments. Hence arises the consistence of Butter, which is the fat part of Milk, that is, of a liquor half-changed into an animal juice.

This explication furnishes us also with the reason why Acids agree so ill with people of weak and delicate constitutions. The motion and heat in their bodies is not sufficient to effect a due combination of the Acids with the Oils. Hence it comes to pass, that, during and after digestion, they find in their bowels the bad effects of those Acids, in the disorder commonly called the Heart-burn. Hence also it is that such people receive great benefit from the use of Absorbents, which uniting with the Acids neutralize them, and relieve nature when she has not strength enough herself to get the better of them.

To return to our analysis of Butter: we took notice in the process that Butter seems to boil with a very moderate heat at the beginning of the distillation, and that in the course of the operation the ebullition ceases entirely, though the heat be then greatly increased; which is contrary to the general rule. The reason is, that butter, though a seemingly homogeneous mass, contains nevertheless some particles of Cheese and Whey. The particles of Whey, being much the lightest, endeavour, on the first application of heat, to extricate themselves from amongst the particles of Butter, and to rise in distillation. Thus they form the drops of acidulated phlegm which come over at first, and, in struggling to get free, lift up the buttery parts, or actually boil, which occasions the ebullition observable at the beginning of the process. When they are once separated, the melted Butter remains calm and smooth without boiling. If you want to make it boil you must apply a much greater degree of heat; which you cannot do in close vessels, without spoiling the whole operation: because the degree of heat necessary for that purpose would force up the Butter in substance, which would rush over into the receiver, without any decomposition. Indeed if the vessels were luted they would be in danger of bursting.

As to the caseous parts, which are mixed with fresh Butter, they also separate at the beginning of the distillation, when the Butter is melted, and gather on its surface in a scum. These particles of Cheese and Whey, which are heterogeneous to Butter, help to make it spoil the sooner. And for this reason those who want to keep Butter a long time, without the use of salt, melt it, and thereby evaporate the aqueous parts. The lightest portion of the particles of Cheese rises to the surface, and is skimmed off; the rest remains at the bottom of the vessel, from which the Butter is easily separated, by decanting it while it is yet fluid.

Butter may also be distilled, by incorporating it with some additament which will yield no principle itself, nor retain any of those of the Butter. I have distilled it in this manner with the additament of fine sand: the operation succeeds very well, is sooner finished, and more easily conducted: but I chose to describe here the manner of doing it without additament; because the several changes, which the Butter undergoes in the retort during the operation, may be better observed.

If you desire to convert the Butter wholly into Oil, you must take the fixed matter you find in the receiver, and distil it once more, or oftener, according to the degree of fluidity you want to give it. The case is the same with this matter as with all other thick Oils, which, the oftener they are distilled, grow always the more fluid, because in every distillation they are separated from part of the Acid, to which alone they owe their consistence.

PROCESS III.

When it begins to run but very slowly raise your fire. There will come over a yellow Oil, somewhat empyreumatic. Continue the distillation, still increasing the fire by degrees as occasion requires. The Oil and acid Phlegm will continue to rise; the Phlegm growing gradually more acid, and the Oil deeper coloured, and more empyreumatic. At last, when the retort is almost red-hot, there comes off a second black Oil, of the consistence of Turpentine, very empyreumatic, and so heavy as to sink in water. In the retort will be left a considerable quantity of charred matter.

OBSERVATIONS.

Cheese-curd barely drained, till no more Whey will drip from it, is not entirely freed thereof; and for this reason we directed it to be pressed in a linen cloth, before it be put into the retort to be distilled. Without this precaution, the remaining Whey would rise in a considerable quantity on the first application of heat; and, instead of analyzing the Curd only, we should at the same time analyze the Whey also. This is to be understood of green Curd and new-made Cheese; for, if it be suffered to grow old, it will at length dry of itself: but then we should not obtain from it the same principles by distillation; as it corrupts and begins to grow putrid after some time, especially if it be not mixed with some seasoning to preserve it.

The first Phlegm that rises in this distillation, as in that of Butter, is a portion of the Whey that was left in the Cheese, notwithstanding its being well pressed. This Phlegm grows gradually more acid, being the vehicle of the Acids of the Cheese, which are forced up along with it by the fire.

The Acid obtained from this matter is less in quantity, and weaker, than that of Butter: and accordingly the Oil distilled from Cheese is not fixed like that of Butter. Yet it is remarkable that the last empyreumatic Oil, which is as thick as Turpentine, is heavier than water: a property which it probably derives from the quantity of Acid it retains.

The quantity of charred matter, which remains in the retort after the distillation of Cheese, is much greater than that left by Butter; which proves that the former contains a much greater quantity of earth. These coals are exceeding difficult to burn and reduce to ashes. I have kept them red-hot, in the open air, and in a very strong fire, about six hours, continually stirring them, in order to bring the under parts to the surface, that they might be burnt, yet I could not consume them entirely. They even deflagrated afterwards with Nitre, as if they had not been burnt at all; and yet, during the whole time of their calcination, there appeared constantly a small flame, like that of charcoal, on the surface of the matter.

PROCESS IV.

It will appear, on examining the three analyses of the substances whereof Milk consists, that none of them yields a Volatile Alkali: which I think very worthy of notice; as it is, I believe, the only animal matter from which such a Salt cannot be obtained. It is true, the milk of animals that feed on vegetables may be considered as an intermediate liquor between vegetable and animal substances; as an imperfect animal juice, which still retains much of the vegetable nature: and we actually find that Milk almost always hath, at least in part, the properties of those plants with which the animals that yield it are fed. Yet, as it cannot be formed in the body of the animal, without mixing with several of its juices that are entirely perfected, and become purely animal, it must appear strange that the analysis thereof should not afford the least vestige of that principle, which all other animal matters yield in the greatest plenty.

I imagine the reason of this may be found in the use to which Milk is destined. It is intended for the nourishment of animals of the same species with those in whose bodies it is produced. Consequently it ought as much as possible to resemble the juices of the food which is proper for those animals. Now, as animals that live only on vegetables could not be properly nourished by animal matters, for which nature itself hath even given them an aversion, it is not surprising that the Milk of such animals should be free from any mixture of such things as are unsuitable to the young ones whom it is designed to nourish. There is reason therefore to think that nature hath disposed the organs, in which the secretion of Milk is performed, so as to separate it entirely from all the animal juices first mixed with it: and this I take to be the principal difference between Milk and Chyle; the latter being necessarily blended with the saliva, the gastric and pancreatic juices, the bile and lymph, of the animals in which it is formed. Hence it may be concluded, that, if a quantity of Chyle could be collected sufficient to enable us to analyze it, the analysis thereof would differ from that of Milk, in this chiefly that it would yield a great deal of Volatile Alkali, of which Milk, as hath been said, yields none at all.

The same thing probably takes place in carnivorous animals. It is certain that those animals chuse to eat the flesh of such others only as feed upon vegetables; and that nothing but extreme hunger, and the absolute want of more agreeable food, will force them to eat the flesh of other carnivorous animals. Wolves, which greedily devour sheep, goats, &c. seldom eat Foxes, Cats, Polecats, &c. though these animals are not strong enough to resist them. Foxes, Cats, and Birds of prey, that make such terrible havock among wild fowl, and other sorts of game, do not devour one another. This being laid down, there is reason to think that the Milk of carnivorous animals is something of the nature of the flesh of those animals that feed on vegetables, and which they chuse to eat, and not of the nature of their own flesh; as the Milk of animals that feed on vegetables is analagous to the juice of vegetables, and when analyzed yields no Volatile Alkali, though every other part of their body does.

But whatever be the nature of Milk, and of whatever ingredients it be formed, it always contains the three several substances above-mentioned; namely, the fat, or Buttery part, properly so called, the Cheesy, and the Serous part, the last of which we are now examining. It is, properly speaking, the Phlegm of the Milk, and consists almost entirely of water. For this reason it is proper to lessen the quantity thereof considerably by evaporation, so that its other principles, being concentrated and brought nearer together, may become much more sensible. There is no danger of losing any essential part of the Whey in the evaporation, if it be performed in the balneum mariæ, with such a gentle heat as may carry off the aqueous parts only: this greatly shortens the analysis, which will prove exceeding long and tedious, if all the water be distilled off in close vessels.

As Whey is chiefly the aqueous part of Milk, as said above, it must contain all the principles thereof that are soluble in water; that is, its saline and saponaceous parts. And accordingly the analysis thereof shews that it contains an Oil, rendered perfectly saponaceous by an Acid; that is, made perfectly miscible with water. This quality of the Oil contained in Whey appears from the perfect transparency of that liquor, which we know is the mark of a complete dissolution. In the distillation of Whey, the saponaceous matter contained therein is decomposed; the saline part rises first, as being the lightest; this is the Acid taken notice of in the process; after which the Oil, now separated from the principle which rendered it miscible with water, comes over in its natural form, and doth not afterwards mix with the aqueous part.

Besides the saponaceous matter, Whey contains also another saline substance; namely, Sea-Salt: this is obtained by lixiviating the caput mortuum left in the retort, which, because of its fixedness, cannot rise with the other principles in distillation. To this Salt it is owing that what remains in the retort after distillation grows moist in the air; for we know that Sea-salt thoroughly dried hath this property.

The fixed Alkaline Salt, obtained from the caput mortuum burnt to ashes, proves that Milk still retains something of the vegetable nature: for the following analysis will shew us that matters purely animal yield none at all.

CHAP. II.

Of the Substances which compose an Animal Body.

PROCESS I.

Blood, while circulating in the body of a healthy animal, and when newly taken from it, hath a mild taste, which discovers nothing like either an Acid or an Alkali; nor doth it shew any sign of either the one or the other in Chymical trials. When tasted with attention it betrays something like a savour of Sea-salt; because it actually contains a little thereof, which is found in the charred matter left in the retort after distillation, when carefully examined.

We shewed that Milk also contains a little of this Salt. It enters the bodies of animals with the food they eat, which contains more or less thereof according to its nature. It plainly suffers no alteration by undergoing the digestions, and passing through the strainers, of the animal body. The case is the same with the other Neutral Salts which have a Fixed Alkali for their basis: we find them unchanged in the juices of animals into whose bodies they have been introduced. They are incapable of combining, as Acids do, with the oily parts; and so are dissolved by the aqueous fluids, of which nature makes use to free herself from those Salts, and discharge them out of the body; as shall be shewn when we come to speak of Urine and Sweat.

Blood, like all other animal matters, is, properly speaking, susceptible of no fermentation but that of putrefaction. Yet it turns somewhat sour before it putrefies. This small degree of acetous fermentation is most sensible in flesh; and especially in the flesh of young animals, such as calves, lambs, chickens, &c.

The quantity of pure water, which Blood, in its natural state, contains, is very considerable, and makes almost seven eighths thereof. If it be distilled, without being first dried, the operation will be much longer; because it will be necessary to draw off all this insipid phlegm with a gentle fire. There is no reason to apprehend that, by drying Blood in open vessels as directed, any of its other principles will be carried off with its Phlegm: for it contains no other substance that is volatile enough to rise with the warmth of a balneum mariæ. This may be proved by putting some undried Blood into a glass cucurbit, fitting thereto a head and receiver, and distilling, in a balneum mariæ, all that the heat of the bath, not exceeding the heat of boiling water, will raise: for, when nothing more will come over, you will find in the receiver an insipid phlegm only, scarce differing from pure water, except in having a faint smell like that of Blood; wherein it resembles all the phlegms that rise first in distillation, which always retain something of the smell of the matters from which they were drawn. That part of the Blood, which remains in the cucurbit after this first distillation, being put into a retort, and distilled with a stronger fire, yields exactly the same principles, and in the same proportion, as Blood dried in open vessels in the balneum mariæ: so that, if this Phlegm of Blood contain any principles, the quantity thereof is so small as to be scarce perceptible.

The Volatile Alkali that rises with the Oil, when Blood is distilled in a retort with a degree of heat greater than that of boiling water, is either the production of the fire, or arises from the decomposition of an Ammoniacal Salt, of which it made a part. For we shall see, when we come to treat of this saline substance, that it is so extremely volatile as to exceed, in that respect, almost all other bodies that we know: and therefore if this Volatile Alkali pre-existed formally in the Blood, uncombined with any other matter capable, in some measure, of fixing it, it would rise at first almost spontaneously, or at least, on the first application of the gentlest heat. We have an instance of this in Blood, or any other animal matter, that is perfectly putrefied; which containing a Volatile Alkali, either formed or extricated by putrefaction, lets go this principle when distilled, even before the first phlegm: and, for this reason, when putrefied Blood is to be analyzed, it must by no means be dried, like fresh Blood, before distillation; for all the Volatile Alkali would by that means be dissipated and lost at once.

The Volatile Alkali obtained from Blood that hath not undergone putrefaction, affords matter of some speculation. Indeed the separation of this Salt from Blood requires a degree of heat, vastly greater than that which is necessary to make it rise, when it is perfectly formed and disentangled: and this gives room to think that it is the result of a combination formed by the fire, during the distillation. But then this same degree of heat neither separates nor forms any Volatile Alkali in a great number of plants, or in milk, as hath been shewn. Yet it cannot be supposed that the blood of animals, which feed only on those plants or on milk, is any other than these very matters digested and rendered perfectly animal substances: whence it must be concluded, that, when vegetable substances are converted into animal substances, they undergo such alterations as render them capable of yielding, when analyzed, a principle that was not discoverable in them before. Now we know that this same principle, that is, the Volatile Alkali, is the product of putrefaction, or, which is the same thing, of the last degree of fermentation: and this, I think, makes the opinion of those more than probable, who believe that trituration and mechanical motion are not the only causes, that effect the conversion of food into an animal juice, but that fermentation hath a great share in this change. It is true, we do not find, in animal matters, any manifest token of an Ardent Spirit, an Acid, or a Volatile Alkali; nor, consequently, any substance that is an evident production of any of the three different degrees of fermentation: and yet, as substances perfectly animalized are exactly in the same state with vegetables that have undergone the first, and even the second, degree of fermentation, so that they are susceptible of putrefaction only, (or, at least, if they shew at first some faint tokens of acidity, they run immediately and rapidly into complete putrefaction); it is nevertheless probable, that vegetable matters, in order to their becoming animal substances, undergo certain changes and alterations, which have some resemblance with those produced by fermentation.

This opinion is further confirmed by two other analogies, between animal matters, and vegetables advanced to the last stage of fermentation; which is, that they yield neither an Essential Oil nor a Fixed Alkali: for the coal, that remains in the retort after the distillation of Blood, being burnt in an open fire, discovers no Fixed Alkali in its ashes.

The want of a Fixed Alkali in animal matters arises from hence, that their Acid is nearly in the same state with the Acid of vegetable matters which have undergone putrefaction; that is, it is so subtilized and attenuated, as to be fit to enter into the combination of a Volatile Alkali, and is no longer so intimately united with the fixed earth as to produce therewith a Fixed Alkali in the fire.

Though Blood and other animal matters afford no Fixed Alkali, but, on the contrary, yield much Volatile Alkali, it doth not therefore follow that all the Acid, which those substances contained before they were analyzed, is employed in the production of a Volatile Alkali. We shall hereafter take notice of an animal matter which contains a great deal of Acid: and, not to depart from our present subject, it doth not appear to me to be a settled point among Chymists, whether or no Blood, when analyzed, yields a portion manifestly acid, and possessing all the properties of an Acid.

Mr. Boerhaave, with some other Chymists, makes no mention of any Acid in his analysis of Blood. Mr. Homberg, on the contrary, says[18] expressly, that he constantly obtained an Acid from the Blood and flesh of different sorts of animals, of which he analyzed a great number. Mr. Boerhaave's authority is very respectable, and of great weight: on the other hand, Mr. Homberg's experiments are very conclusive, seem to be made with great care, and are all affirmative. This apparent diversity in the same analysis, delivered by these two great men, determined me to analyze Blood myself, and to examine scrupulously all the principles I could obtain from it.

I therefore distilled some Bullock's Blood in a retort with degrees of fire. Some Phlegm came over first, and then a Volatile Spirit. I changed my receiver; and on increasing the fire there arose, with the Volatile Spirit, a yellow Oil, a Volatile Salt in a concrete form, a russet liquor which smelled strong of Volatile Alkali, and seemed at first to be only a Spirit impregnated with much of that Salt: at last came a very thick fetid Oil.

In this brown liquor, which comes off towards the end of the distillation, Mr. Homberg affirms the Acid to be contained: but, as it certainly is replete with a Volatile Alkali also, he alledges that it contains, at the same time, both a Volatile Alkali and the animal Acid; that these two Salts are distinct from each other, and not combined together in the form of an Ammoniacal Salt; that each of consequence possesses its peculiar properties; and that this liquor is at the same time both Acid and Alkaline; that it effervesces with Acids, and also changes the blue colours of plants to red.

The Alkaline quality of this liquor is very evident, and discovers itself in every Chymical trial; but the same cannot be said of its Acid property. I dropped some of it on blue paper, the colour of which did not at first change in the least, nor acquire the faintest shade of redness. This experiment almost determined me to conclude that Mr. Homberg was mistaken: but some time afterwards I perceived that the blue paper began to turn red where it had been wetted, and that the red colour grew deeper and deeper as the paper dried: and this convinced me, that this liquor actually contains an Acid, as Mr. Homberg asserted; but, that the Volatile Alkali in this liquor, being much more copious than the Acid, had first entered the paper, and hindered the Acid from turning it red as usual; and that, as the Alkali evaporated, the Acid began to act, and produce the customary effect. Hence we see that the Acid of Blood, though extricated by distillation, is not easily perceived at first, because of the great proportion of Volatile Alkali, with which the liquor containing it is impregnated. This is probably what prevented its being discovered by several Chymists, who, it seems, did not suspect its existence, and therefore did not look for it.

Mr. Homberg takes no notice of this little difficulty in his Memoir: but he relates an experiment which might have given occasion to suspect it. It is in his analysis of Human Blood. As the Acid in Human Blood is in less quantity, and less perceptible, than in the Blood of animals that live wholly on vegetables, he directs a second distillation of the brown liquor, which contains at once both the Volatile Alkali and the Acid, till very little thereof be left in the retort. This residuum, says he, contains a very perceptible and distinct Acid. There is reason to believe, from Mr. Homberg's directing the saline liquor to be distilled again, that he did not find the Acid sufficiently perceptible in it at first. Now a second distillation is a very good way to render it much more sensible. For though this animal Acid be volatile, the Volatile Alkali is still vastly more so; and therefore if the liquor containing both these saline substances be distilled, the Volatile Alkali must needs rise first, and leave the Acid alone, or almost alone, at the bottom of the retort. This is exactly the case in our experiment on blue paper; the operation being here performed with a small quantity, and much more expeditiously, as appears from our account of it.

It is not at all surprising that the Volatile Alkali and animal Acid, though confounded in the same liquor, should not be united together and converted into a Neutral Ammoniacal Salt. Mr. Homberg pretends that these two saline matters do not act upon each other, because they are too much dephlegmated. The oily parts, with which they are both loaded, may also contribute thereto: nor is this unprecedented; the same thing being observed of the Acid and the Volatile Alkali of several vegetable substances.

Mr. Homberg, justly suspecting that there might be some difference between the condition of the Acid in the Blood of animals that feed altogether on vegetables, and that in the blood of those that feed only on flesh, examined likewise, by decomposition, the Blood and the flesh of some carnivorous animals. In these also he found an Acid; and it doth not appear that he observed any great difference, in this respect, between their Blood and that of other animals. The difference he found between the Blood of young, and that of grown, or old, animals, with respect to the Acid, seems, by his account, to be more considerable; the Blood of the former containing much more of it than that of the latter: and this is so much the more probable, as we know that the flesh of young animals grows sour, before it putrefies, more sensibly than that of old ones.

We shall conclude this head with a remark concerning the management required in distilling Blood. When the operation is advanced to a certain point, the matter contained in the retort often swells so as to stop the neck of that vessel entirely, and by that means makes it burst with an explosion. To avoid this inconvenience, a very small quantity of Blood must be put into the retort, and the fire must be governed very warily. I have also found that this accident may generally be prevented by mixing the Blood with some matter that can afford no principle by distillation; such as pounded glass or fine sand.

>PROCESS II.

Mr. Geoffroy observes, that the first phlegm, drawn off from it in the balneum mariæ, produces a white precipitate in a solution of Corrosive Sublimate; which shews it to contain a little Volatile Alkali: but the quantity thereof must be very small; seeing the phlegm that contains it smells only like broth, and not like a Volatile Alkali; one particle of which, we know, is capable of affecting the organ of smelling very sensibly. As to the Acid of flesh, there is great reason to believe that it is conditioned exactly like that of Blood.

The ashes of the caput mortuum of flesh, burnt in an open fire, attract the moisture of the air, as Mr. Geoffroy remarks, and increase in weight, though they contain no Fixed Alkali. However, this is not at all surprising; since they contain some Sea-salt, the known property whereof is to grow moist in the air.

The flesh of animals contains much matter that is soluble in water. Mr. Geoffroy examined separately that part of flesh which water is capable of dissolving. With this view he boiled four ounces of beef with three pints of water, in a very close vessel, and repeated the operation six times with equal quantities of fresh water; in order to extract, as far as possible, all the juices of the meat. These broths he put all together, the last of them having but a faint smell of very weak veal broth: he evaporated them over a slow fire, filtering them towards the end of the evaporation, to separate an earthy part; and there remained in the vessel a moderately solid extract, which soon grew moist in the air. This extract, being analyzed, yielded a dram and two grains of Volatile Salt, which adhered to the sides of the receiver; not in ramifications, as Volatile Salts usually do, but in flat crystals, mostly in the form of parallelopipeds. The Spirit and the Oil, which came over together after the Volatile Salt, weighed thirty-eight grains. Salt of Tartar being mixed with this Volatile Salt seemed to increase its strength; which gives room to suspect that the latter contains an Ammoniacal Salt.

The charred matter left in the retort weighed but six grains. Its lixivium gave some tokens of Sea-salt, by making a white precipitate in a solution of quick-silver. The mass of fleshy fibres, that was exhausted by boiling, being dried and analyzed in the same manner, yielded a Volatile Spirit, a Volatile Salt in a concrete form, which stuck to the sides of the receiver in ramifications as usual; and a thick fetid Oil. There now remained in the retort a charred matter, which being burnt in the open air or not burnt, shewed not the least sign of its containing any saline matter.

This method of analyzing flesh, by boiling it at first in water, in order to extract all that can be dissolved by this menstruum, shews us that animal flesh contains an Oil, which is in a saponaceous state: for the extract made therefrom, by water, yields in distillation a considerable quantity of Oil, which was perfectly dissolved in the water, while that extract was in the diluted state of broth, and before it was analyzed.

It is remarkable that the Volatile Salt, yielded by the extract of flesh, is different from that which is obtained out of the flesh itself, when nothing hath been extracted from it. This Salt, as Mr. Geoffroy observed, differs from the common Volatile Alkalis in the form of its crystals; which made that Chymist justly consider it as a Salt of a somewhat Ammoniacal nature; a kind of Essential Salt of flesh.

There is reason to think that this Salt, when dissolved in the water in which we boil flesh, is separated therefrom, by the action of fire, with more ease than while it remains combined with the other principles, in the substance of the flesh; that its separation, in the latter case, requiring a greater degree of heat, it is thereby decomposed; and that the Volatile Alkali, which is obtained from flesh distilled in the usual manner, is only one of the parts that constituted the Ammoniacal Salt thereby decomposed.

The charred matter remaining, after the distillation of flesh first exhausted by boiling, yields nothing saline; because the Sea-salt, which is the only Fixed Salt it could contain, was dissolved by the water together with the matter of the extract.

Mr. Geoffroy likewise examined what parts of flesh Spirit of Wine is capable of dissolving. For this purpose he took four ounces of Beef, dried in the balneum mariæ, poured on it an equal weight of well rectified Spirit of Wine, and left the whole in digestion for a considerable time. The Spirit extracted from the Beef a weak tincture, and separated from it some drops of Oil: it acquired a brown colour, and a faint smell. Mr. Geoffroy found, by several experiments, that the Spirit of Wine had taken up a portion of the Ammoniacal, or Essential, Salt of the flesh. With respect to the Oil, if any at all were dissolved, it could be but very little; for that which the Spirit separated, and which retained its natural form, was certainly not dissolved: seeing in that case it would not have been perceived, but would have made a homogeneous liquor, to appearance, with the Spirit of Wine.

PROCESS III.

The first is, that Bones yielded to boiling water their principles and their Volatile Salts, both sooner and more copiously than flesh did: for in the analysis which Mr. Geoffroy made of several sorts of flesh, though he robbed them in a manner of all their principles by boiling, yet their dried fibres afterwards yielded a considerable quantity of Volatile Salt; whereas the Bones, of which he had made an extract by boiling, afforded him but a very small quantity thereof when analyzed.

The second observation worthy of notice which Mr. Geoffroy made on his analysis of Bones is this; the Salt, which, as was shewn in the analysis of flesh, was resolved by the water wherein he boiled the flesh, and consequently arose when he distilled the extract obtained from that decoction, and crystallized in the form of parallelopipeds, took a quite different turn in the analysis of Bones. None of it appeared in distilling the extract made by decoction, but arose in distilling the boiled Bones, that were exhausted of almost all their other principles by the decoction with water. These differences probably arise from the different contexture of the animal matters in which they are observed.

This analysis of Bones may serve as a pattern for analyzing all the solid parts of animals, such as horns, hoofs, ivory, &c.

PROCESS IV.

It consists almost entirely of Oil: but this Oil is in a concrete form, and observes the general rule of all concreted oily matters, which owe their consistence wholly to the Acid that is combined with them. The rule is evidently so general, that it extends even to the animal kingdom, where, in all other instances, Acids seem to be almost annihilated.

All we said above on the subject of Butter must be applied here: for animal Fat, properly so called, and Butter, do not, in my opinion, differ sensibly from each other, with respect to their analysis. And therefore there is great reason to believe, that what is Butter in Chyle, or Milk, becomes Fat when fixed in the animal body. It is a kind of repository, in which nature lays up and confines the Acid that is unnecessary to the animal composition, and which she could not any other way eliminate.

I made choice of Mutton-Suet for an instance of the analysis of Fat; because this Fat, being the firmest of any, must contain a stronger and more perceptible Acid.

When it is thus distilled, the part which remains fixed hath much less consistence than the Suet had before; which arises from its having lost part of its Acid. Repeated distillations will deprive it of a much greater quantity thereof, and so reduce it into an Oil that will always remain clear and fluid.

Not one particle of Volatile Alkali is obtained by distilling Suet: but then the experiment will not succeed as it ought, unless care be taken to free the Suet perfectly from all the membranes, and all the particles of flesh and blood that may be mixed with it; for, if it should be distilled without this precaution, those heterogeneous matters mingled with it would yield a great deal of Volatile Alkali in distillation; which might impose on the Artist, and make him think the Salt came actually from the Suet. Suet that hath been often melted, as the tallow, for instance, of which candles are made, is sufficiently purified: of this I made use in my analysis, and it yielded me no Volatile Alkali; at least I could perceive none.

In conclusion, all that hath been said, on several occasions, touching the properties of concreted oily matters, may be applied to Suet. I shall only observe here, that it is one of those that manifest no Acidity, and consequently that in its natural state it is not soluble in Spirit of Wine, and only becomes soluble in that menstruum by degrees, as its Acid is extricated by repeated distillations: and on this account it ought to be classed with Bees-Wax, and other oily compounds of that kind.

PROCESS V.

Of the two perfectly distinct substances that constitute the Egg, the Yelk contains the embryo of the chick, and is destined to hatch it: the White is to serve for the nourishment of the chick when it is formed.

These two matters, though they contain the very same principles, yet differ considerably from each other; and chiefly in this, that their principles are not in the same proportions.

The White of an Egg contains so much phlegm, that it seems to consist almost totally thereof. All the aqueous liquor, obtained by distilling it in the balneum mariæ, is, properly speaking, nothing but pure water; for no Chymical trial can discover in it either an Acid or a Volatile Alkali; or any very perceptible Oily part. And yet it must contain some Oil, because the liquor that rises last is a little bitterish to the taste, and smells somewhat of empyreuma. But the principles from which it derives these properties are in too small quantities to be distinctly perceived.

If, instead of distilling the hard White of an Egg, with a view to draw off the great quantity of water it contains, you leave it some time in an air that is not too dry, the greatest part of its moisture separates spontaneously, and becomes very sensible. In all probability this is the effect of a beginning putrefaction, which attenuates this substance, and breaks its contexture. The liquor thus discharged by the White of an Egg thoroughly dissolves Gum-Resins, and particularly Myrrh. If you desire to dissolve Myrrh in this manner, cut a hard-boiled Egg in halves; take out the Yelk; put the powdered Gum-Resin into the cavity left by the Yelk; join the two halves of the White; fasten them together with a thread, and hang them up in a cellar. In a few days time the Myrrh will be dissolved by the moisture that issues from the White of the Egg, and will drop into the vessel placed underneath to receive it. This liquor is improperly called Oil of Myrrh per deliquium.

All the properties of the Whites of Eggs, as well as the principles obtained by analyzing them, are the same with those of the lymphatic part of the blood; so that there is a great resemblance between these two substances.

As to the Yelk, it is plain from its analysis that Oil is the predominant principle thereof. If the Yelk of an Egg be mixed with water, the Oil with which it is replete, and which is by nature very minutely divided, diffuses itself through the whole liquor, and remains suspended therein by means of its viscosity. The liquor at the same time becomes milk-white like an emulsion, and is in fact a true animal emulsion.

In order to obtain the Oil of Eggs by expression with the more ease, care must be taken to chuse Eggs that are seven or eight days old; because they are then a little less viscous. Nevertheless, their viscosity is still so great that they will not easily yield their Oil by expression: and therefore, in order to attenuate and destroy entirely this viscosity, they must be torrefied before they are put to be pressed.

The Oil of Eggs, like all other oily animal matter, seems analagous to the Fat Oils of vegetables. It hath all the properties that characterise those Oils. Its colour is yellow, and it smells and tastes a little of the empyreuma, occasioned by torrefying the Yelks. It is rendered somewhat less disagreeable by being exposed to the dew for thirty or forty nights, if care be taken to stir it often in the mean time.

To conclude: all the principles, both in the Yelk and the White of an Egg, are the same as those found in Blood, Flesh, and all other matters that are perfectly animal.

CHAP. III.

Of the Excrements of Animals.

PROCESS I.

OBSERVATIONS.

Mr. Homberg made a great many experiments on the dung of animals; concerning which he composed two Memoirs published in the Academy's collection for 1711. That Chymist tells us, that, in distilling Excrement, he aimed not so much at discovering the principles of which it consists, as he was desirous to satisfy a friend of his, who had earnestly entreated him to try whether he could not extract therefrom a clear Oil, having no bad smell; because he had seen, as he said, Mercury fixed into pure Silver by such an Oil.

Mr. Homberg's labour had the usual fate of all enterprises of this nature. He actually found the art of drawing from Excrement a clear scentless Oil; but, in whatever way he applied it to Mercury, it produced no change in that metallic substance. However, as Mr. Homberg was a man of sagacity, and knew how to improve every hint offered by his experiments, he made several curious discoveries on this occasion; of which we shall give a concise account, after we have made some remarks on the principles obtained from Excrement by the method described in the process.

This substance, consisting of matters subject to putrefaction, hath constantly a fetid smell, like that of all putrid matters; having been for some time confined in a warm, moist place, which we know promotes putrefaction, and even quickly produces it. Yet the analysis thereof proves that it is not putrefied, or at least not entirely so: for all putrefied matters contain a Volatile Alkali perfectly formed and extricated; and, as this principle rises with less heat than that of boiling water, it always comes over first in distillation. Now we have seen that, with the heat of boiling water, it parts with nothing but an insipid phlegm, containing no Volatile Alkali: a sure proof that the fecal matter is not completely putrefied.

There is nothing remarkable in the Volatile Salt and fetid Oil, which rise with a degree of heat greater than that of boiling water. They are common productions, of which we have made frequent mention in several of the preceding analyses; and therefore they need not now detain us from proceeding to give a summary account of Mr. Homberg's chief discoveries.

One of the methods by which Mr. Homberg endeavoured to obtain from Excrement a clear Oil, without any bad smell, was to separate its earthy and gross parts, by filtering it before he distilled it. "For this purpose he diluted Excrement newly discharged with hot water, using a quart of water to an ounce of feces. Then he let the mixture stand to cool, and, the gross parts falling to the bottom, he poured off the water by inclination. This liquor he filtered through brown paper, and evaporated to a pellicle over a gentle fire. There shot in it long crystals of four, five, and six sides, which Mr. Homberg thinks may be called the Essential Salt of Excrement. They resemble Salt-petre, in some measure, and deflagrate in the fire much like it; with this difference, that their flame is red, and they burn slowly; whereas the flame of Salt-petre is white and very vivid: probably, says Mr. Homberg, because there is too much of an oily matter in the one, and less in the other.

"Mr. Homberg distilled this Salt in a glass retort with degrees of fire, and at last with a very violent one. At first there came over an aqueous liquor, sharp and acid, which was followed by a brown fetid oil, smelling very strong of empyreuma. This distillation he attempted four several times; and each time the matter in the retort took fire, just when the Oil began to come off."

The Salt which Mr. Homberg obtained from excrement is very remarkable. We shall have occasion to speak of it in another place, and shall only observe here, that its Nitrous character is by no means ambiguous: its deflagrating on live coals convinced Mr. Homberg of its being a true Nitre. But its constantly taking fire in the retort, as oft as distilled, is a sure proof that it is a Nitrous Salt: for Nitre only hath the property of thus taking fire in close vessels, and making other combustible matters burn along with it.

The process by which Mr. Homberg at last obtained from Excrement a clear oil without any bad smell is curious, and worthy of a place here; on account of the views and occasions of reflection which it may open.

"Mr. Homberg having tried in vain, by distilling Excrement a great many different ways, to obtain from it such an Oil as he wanted, resolved to employ fermentation, the effect whereof is to change the disposition of the principles of mixts. With this view he dried some Excrement in the water-bath, and, having pulverized it, poured thereon six times its weight of phlegm that had been separated from it by distillation, and put the whole into a large glass cucurbit, covered with an inverted vessel that fitted exactly into it, and was close luted. This vessel he set in a balneum mariæ for six weeks, keeping up such a gentle heat as would not burn one's hand; after which he uncovered the cucurbit, and having fitted thereto a head and a receiver, distilled off all the aqueous moisture in the balneum mariæ with a very gentle heat. It had now lost almost all its bad smell, which was changed into a faint one. It came over somewhat turbid, whereas it was very clear when put into the cucurbit. Mr. Homberg found this water to have a cosmetic virtue: He gave some of it to persons whose complexion, neck, and arms, were quite spoiled, being turned brown, dry, rough, and like a goose skin: they washed with it once a day, and, by continuing the use of this water, their skin became very soft and white."

The dry matter, that remained in the bottom of the cucurbit after distillation, had lost about a twentieth part of its weight; that is, of twenty ounces, put at one time into the cucurbit, somewhat less than nineteen ounces remained. Mr. Homberg suspects that it was not so dry when put into the cucurbit as when it was taken out. Perhaps also the species of fermentation which the matter underwent had attenuated and volatilized some part of it; so that it came over with the phlegm in distillation. The turbidness of that phlegm, which was clear and limpid before, seems to countenance this conjecture.

"The dry matter left in the cucurbit after the first distillation, had not the least smell of feces: on the contrary, it had an agreeable aromatic odour; and the vessel in which Mr. Homberg had digested it, being left open in a corner of his laboratory, acquired in time a strong smell of Ambergris. It is surprising, as Mr. Homberg justly observes, that digestion alone should change the abominable smell of Excrement into an odour as agreeable as that of Ambergris.