1. Introduction.—In the first volume the principal plant foods occurring in soils have been named and the methods of estimating them described. As fertilizers are classed those materials which are added to soils to supply supposed deficiencies in plant foods, or to render more available the stores already present. There is little difference between the terms fertilizer and manure. In common language the former is applied to goods prepared for the farmer by the manufacturer or mixer, while the latter is applied to the stores accumulated about the stables or made elsewhere on the farm. Thus it is common to speak of a barnyard or stall manure and of a commercial fertilizer.

One of the objects of the analysis of soils, as described in the first volume of this work, is to determine the character of the fertilizer which should be added to a field in order to secure its maximum fertility.

One purpose of the present part is to determine the fitness of offered fertilizing material to supply the deficiencies which may be revealed by a proper study of the needs of the soil.

2. Natural Fertilizers.—In the succession of geologic epochs which has marked the natural history of the earth there have been brought together in deposits of greater or less magnitude the stores of plant food unused by growing crops or which may once have been part of vegetable and animal organisms. Some of these deposits have been mentioned in the first volume, paragraphs 11, 12, and 18.

For a full description of the extent and origin of these deposits the reader is referred to works on economic geology. These deposits are the chief sources of the commercial fertilizers which are offered to the farmers of to-day and to which the agricultural analyst is called upon to devote much of his time and labor. The methods of determining the chemical composition and agricultural value of these deposits, as practiced by the leading chemists of this country and Europe, will be fully set forth in the following pages.

3. Waste Matters as Fertilizing Materials.—In addition to the natural products just mentioned the analyst will be called on also to deal with a great variety of waste materials which, in the last few years, have been saved from the débris of factories and abattoirs, and prepared for use on the farm. Among these waste matters may be mentioned, bones, horns, hoofs, hair, tankage, dried blood, fish scrap, oil cakes, ashes, sewage, and sewage precipitates, offal of all kinds, leather scraps, and organic débris in general.

It is important, before beginning an analysis, to know the origin of the substances to be determined. As has already been pointed out in volume first the process which would be accurate with a substance of a mineral origin might lead to error if applied to the same element in organic combination. This is particularly true of phosphorus and potash. A simple microscopic examination will usually enable the analyst to determine the nature of the sample. In this manner, in the case of a phosphate, it would at once be determined whether it was bone, mineral, or basic slag. The odor, color, and general consistence will also aid in the determination.

4. Valuation of Fertilizing Ingredients.—Perhaps there are no more numerous and perplexing questions propounded to the analyst than those which relate to the value of fertilizing materials. There is none harder to answer. As a rule these questions are asked by the farmer, and refer to the fertilizers put down on his fields. In such cases the cost of transportation is an important factor in the answer. The farther the farmer is removed from the place of fertilizer manufacture the greater, as a rule, will be the cost. Whether the transportation is over land or by water also plays an important part in the final cost. The discovery of new stores of fertilizing materials has also much to do with the price. This fact is especially noticeable in this country, where the price of crude phosphates at the mines has fallen in a few years from nearly six dollars to three dollars and forty-three cents per ton[1]. This decrease has been largely due to discoveries of vast beds of phosphatic deposits in Florida, North Carolina, Tennessee, and Virginia. The state of trade, magnitude of crops, and the vigor of commerce also affect, in a marked degree, the cost of the raw materials of commercial fertilizers.

5. Trade Values of Fertilizing Ingredients in Raw Materials and Chemicals.—The values proposed by the Massachusetts Experiment Station are given below.[2]

The manurial constituents contained in feed stuffs are valued as follows:

The organic nitrogen in superphosphates, special manures, and mixed fertilizers of a high grade is usually valued at the highest figures laid down in the trade values of fertilizing ingredients in raw materials; namely, eighteen and one-half cents per pound, it being assumed that the organic nitrogen is derived from the best sources; viz., animal matter, as meat, blood, bones, or other equally good forms, and not from leather, shoddy, hair, or any low-priced, inferior form of vegetable matter, unless the contrary is evident. In such materials the insoluble phosphoric acid is valued at two cents a pound. These values change as the markets vary.

The scheme of valuation prepared by the Massachusetts station does not include phosphoric acid in basic slags. By many experimenters the value of the acid in this combination, tetracalcium phosphate, is fully equal to that in superphosphates soluble in water and ammonium citrate. It would perhaps be safe to assign that value to all the phosphoric acid in basic slags soluble in a five per cent citric acid solution.

Untreated fine-ground phosphates, especially of the soft variety, so abundant in many parts of Florida, have also a high manurial value when applied to soils of an acid nature or rich in humus. On other soils of a sandy nature, or rich in calcium carbonate, such a fertilizer would have little value. The analyst in giving an opinion respecting the commercial value of a fertilizer, must be guided not only by the source of the material, its fineness or state of decomposition, and its general physical qualities, but also by the nature of the crop which it is to nourish and the kind of soil to which it is to be applied.

GENERAL ANALYTICAL PROCESSES.

6. Taking Samples.—It is impracticable to give definite directions for taking samples of fertilizers which will be applicable to all kinds of material and in all circumstances. If the chemist himself have charge of the taking of the sample, it will probably be sufficient to say that it should accurately represent the total mass of material sampled. Generally the samples which are brought to the chemist have been taken without his advice or direction and he is simply called upon to make an analysis of them.

7. Minerals Containing Fertilizing Materials.—When possible, the samples should be accompanied by a description of the mines where they are procured and a statement of the geologic conditions in which the deposits were made. As large a quantity of the material as can be conveniently obtained and transported should be secured. Where a large quantity of mineral matter is at hand it should first be put through a crusher. Many forms of crusher, driven by hand and other power, are on the market. Among these may be mentioned the Alden, Blake, Bisworth, Forster, and Lipsay machines.[3] They are all constructed essentially on the same principle, the pieces of mineral being broken into small fragments between two heavy vibrating steel plates. The general form of these instruments is seen in Fig. 1.

The fragments coming from the crusher can be reduced to a coarse powder by means of the iron plate and crusher shown in Fig. 2.

Where only a small quantity of mineral is at hand the apparatus just mentioned may be used at once after breaking the sample into small fragments by means of a hammer.

Finally the sample, if to be dissolved in an acid or soluble materials only, is reduced to a powder in an iron mortar until it will pass a sieve with a one or, better, one-half millimeter circular mesh. The powder thus obtained must be stirred with a magnet to remove all iron particles that may have been incorporated with the mass by abrasion of the instruments employed.

If a complete mineral analysis of the sample is to be secured, the material freed from iron, as above described, is to be rubbed to an impalpable powder in an agate mortar.

8. Mixed Fertilizers.—In fertilizing materials in bulk, the first requisite is that they shall be thoroughly mixed so that a given volume of the material may represent, practically, definite quantities of the materials sampled. The finer the material is, in the original state, and the more thoroughly it has been mixed, the better the sample will be. If the sample be already in sacks it will be sufficient to take portions by means of the ordinary trier, such as is used for sampling sugar and other substances. This consists of a long metal implement such as would be formed by a longitudinal section of a tube. The end is pointed and suited for penetrating into the sack and the materials contained therein. On withdrawing it, the semi-circular concavity is found filled with the material sampled. Samples in this way should be taken from various parts of the sack and these samples well mixed together and a subsample of the amount necessary to be taken to the laboratory can then be obtained.

9. Method of the French Experiment Stations.—In the method employed by the French Experiment Stations it is directed that in no case should stones or other foreign particles be removed from the fertilizer sampled, but they should enter into the sample taken in, as nearly as possible, the same proportions as they exist in the whole mass.

In the case of stones or other solid masses which are to be sampled, as many samples as possible should be taken from all parts of the heap and these should be reduced to a coarse powder, thoroughly mixed together and sampled.

In case the material is in the form of a paste, if it is homogeneous, it will be sufficient to mix it well and take the sample directly; but in case there is a tendency for the pasty mass to separate into two parts, of which the one is a liquid and the other, more of a solid consistence, it may be well to take samples from each in case they can not be thoroughly incorporated by stirring.

10. Method of the French Association of Sugar Chemists.—The method adopted by the French sugar chemists directs that the sample should be taken from the fertilizer in bulk or from a portion used for industrial purposes.[4] The sample for analysis is to be taken from the above sample after it has been sent to the laboratory. The method of taking should be varied according to the condition of the substances to be analyzed.

The large sample selected from the goods delivered to commerce having been delivered at the laboratory, the analytical sample is taken as follows:

When the industrial sample, more or less voluminous, reaches the laboratory, the chemist is to begin by taking a note of the marks, labels, and descriptions found thereon, and of the nature and state of the package which contains it, and the date of its arrival. All this information should be entered upon the laboratory book and afterwards transcribed on the paper containing the results of the analysis, as well as the name of the person sending it. This having been done, the sample is to be properly prepared in order that a portion may be taken representing exactly the mean composition of the whole.

If it is in a state of fine powder, such as ground phosphates and certain other fertilizers, it is sufficient to pass it two or three times through a sieve with meshes one millimeter in diameter, taking care to break up the material each time in order to mix it and to pulverize the fragments which the sieve retains. The whole is afterwards spread in a thin layer upon a large sheet of paper, and a portion is taken here and there upon the point of a knife until about twenty grains are removed, and from this the portion subjected to analysis is afterwards taken.

If the sample comes in fragments, more or less voluminous, such as phosphatic rocks or coarsely pulverized guanos containing agglomerated particles, it is necessary first to reduce the whole to powder by rubbing it in a mortar or in a small drug mill. It is next passed through a sieve of the size mentioned above and that which remains upon the sieve pulverized anew until all has passed through. This precaution is very important, since the parts which resist the action of the pestle the most have often a composition different from those which are easily broken.

When the products to be analyzed contain organic materials, such as horn, flesh, dry blood, etc., the pulverization is often a long and difficult process, and results in a certain degree of heating which drives off some of the moisture in such a way that the pulverized product is at the last drier, and, consequently, richer than the primitive sample. It is important to take account of this desiccation, and since the pulverization of a mass so voluminous can not be made without loss, the determination of the total weight of the sample before and after pulverization does not give exact results.

In such a case it is indispensable to determine the moisture, both before and after pulverizing, and to calculate the analytical results obtained upon the pulverized sample back to the original sample.

In order to escape this necessity, as well as the difficulties resulting from the variations in moisture during transportation, some chemists have thought it better to always dry the commercial products before submitting them to analysis, and to report their results in the dry state, accompanied by a determination of the moisture, leaving thus to the one interested the labor of calculating the richness in the normal state, that is to say, in the real state in which the merchandise was delivered.

In addition to the fact that this method allows numerous chances of errors, many substances undergoing important changes in their composition by drying alone, it has been productive of the most serious consequences. The sellers have placed their wares on the market with the analysis of the material in a dry state, and a great number of purchasers have not perceived the fraud concealed under this expression so innocent in appearance. It is thus that there has been met with in the markets guano containing twenty-five per cent of water, which was guaranteed to contain twelve per cent of phosphoric acid, when, in reality, it contained only eight per cent in the moist state.

11. Barn-Yard Manures.—The sampling of stall and barnyard manures is more difficult on account of the fact that the materials are not homogeneous and that they are usually mixed with straw and other débris from the feed trough, and only the greatest care and patience will enable the operator to secure a fair sample.

In the case of liquid manures the liquid should be thoroughly stirred before the sample is taken.

Frear points out the difficulty of securing representative samples of stall manure and describes methods of removing it.[5] The stall manure sampled had been piled in the cattle-yard for a time and the cattle were allowed to run over the heaps for an hour or two each day. Pigs were also allowed free access to the heaps in order to insure a more perfect mixture of the ingredients.

Twenty-nine loads of 3,000 pounds each were taken from the exposed heap and thirty-four loads of 2,000 pounds each were taken from the covered heap. From each load were removed two carefully selected portions of ten pounds each, which were placed in separate covered boxes numbered A and B. When the sampling was completed these boxes were covered. After being removed to the laboratory the boxes were weighed and the contents thoroughly mixed. Two samples of twelve liters volume each, were drawn from each box. One-third of this was chopped in a large meat chopper and the other two-thirds taken into the laboratory without being cut. These samples, on entering the laboratory, were weighed and dried at a temperature of 60°. Smaller samples were then drawn from each of these and ground in a drug mill for analysis. Duplicate samples taken in this way, while they did not give absolutely concordant results, showed a near approximation. A more careful sampling on the line proposed would, in all probability, secure absolutely agreeing results in duplicate samples.

12. Preparation of Sample in Laboratory.—The method of preparing mineral fertilizers for analysis has been given under directions for sampling. Many difficulties attend the proper preparation of other samples, and the best approved methods of procedure are given below:

According to the directions given by the Association of Official Agricultural Chemists the sample should be well intermixed, finely ground, and passed through a sieve having circular perforations one millimeter in diameter.[6] The processes of grinding and sifting should take place as rapidly as possible so that there may be no gain or loss of moisture during the operation.

13. Method of the French Agricultural Stations.—The manner of proceeding recommended by the French stations varies with the fertilizer.[7] If it is not already in the form of a powder it is necessary to pulverize it as finely as possible by rubbing it up in a mortar. In certain cases, as with superphosphates, the material should be passed through a sieve having apertures of one millimeter diameter, all the larger parts being pulverized until they will pass this sieve.

When the matters are too pasty to be divided in the mortar they should be divided by means of a knife or a spatula. They should then be incorporated with a known weight of inert, pulverulent matter such as fine sand, with which they should be thoroughly mixed and in subsequent calculations the quantity of sand or other inert matter added must be taken into consideration. Usually a pasty state of a fertilizer is due to the humidity of the mixture. In this case a considerable volume of the sample is taken and dried and then reduced to a pulverulent state. In the subsequent calculations, however, the percentage of moisture lost must be taken into consideration.

Before drying a sample it is necessary to take into consideration whether or not the product will be modified by desiccation as would be the case, for instance, with superphosphates. With these, which are often in a state more or less agglomerated, it is recommended to introduce into them, in order to divide them, a certain quantity of calcium sulfate in order to obtain them in a pulverulent state.

In the case of animal débris they should be divided as finely as possible with the aid of scissors and then passed through a drug mill if dry enough. They are then mixed by hand and may finally be obtained in a state of considerable homogeneity.

When fertilizers are in a pasty state more or less liquid, they are dried at 100°, first introducing a little oxalic acid in case they contain any volatile ammoniacal compounds. The product of desiccation is then passed through a mill. Before treating in this way it is necessary to be sure that the composition will not be altered by drying. In the case of a mixture containing superphosphates and nitrate, for instance, drying would eliminate the nitric acid. In such a case the free phosphoric acid should be neutralized with a base like lime. In the case of fertilizers containing both nitrates and volatile ammoniacal compounds the addition of oxalic acid might also set free nitric acid during the desiccation. In such a case it is necessary to dry two samples; one with the addition of oxalic acid for the purpose of estimating the ammonia, and the other without the acid for the purpose of estimating the nitrate. A qualitative analysis should precede all the operations so as to determine the nature of the material to be operated on.

14. German Method.—In the method pursued by the German experiment stations it is directed:[8]

(1) Dry samples of fertilizers must be passed through a sieve and afterwards well mixed.

(2) With moist fertilizers, which can not be subjected to the above process, the preparation should consist in a careful and thorough mixing, without sieving.

(3) On the arrival of the samples in the laboratory their weight should be determined. The half of the sample is prepared for analysis and the other part, to the amount of a kilo, should be placed in a glass vessel, closed air-tight, and placed in a cool place for at least a quarter of a year from the time of its reception, in order that it may be subjected to any subsequent investigations which may be demanded.

(4) In the case of raw phosphates and bone-black the amount of water which they contain should be determined at from 105° to 110°. Samples which in drying lose ammonia in any way, should have this ammonia determined.

(5) Samples which are sent to other laboratories for control analyses, should be sent securely packed in air-tight glass bottles.

(6) The weight of the samples sent should be entered in the certificates of analysis.

(7) Samples which, on pulverizing, change their content of water, must have the water content estimated in both the coarse and powdered condition and the results of the analysis must be calculated to the water content of the original coarse substance.

15. Special Cases.—Many cases arise of such a nature as to make it impossible to lay down any rule which can be followed with success. As in almost every other process in agricultural chemistry the analyst in such cases must be guided by his judgment and experience. Keeping in view the main object, viz., to secure in a few grams of material a fair representation of large masses he will generally be able to reach the required result by following the broad principles already outlined. In many cases the details of the work and the adaptations necessary to success must be left to his own determination.

16. Drying Samples of Fertilizers.—The determination of the uncombined moisture in a sample of fertilizer is not an easy task. In some cases, as in powdered minerals, drying to constant weight at the temperature of boiling water is sufficient. In organic matters containing volatile nitrogenous compounds, these must first be fixed by oxalic or sulfuric acid, before the desiccation begins. If any excess of sulfuric acid be added, however, drying at 100° becomes almost impossible. Particular precautions must be observed in drying superphosphates. In drying samples preparatory to grinding for analysis, it is best to stop the process as soon as the materials can be pulverized. In general, samples should be dried only to determine water, and the analytical processes should be performed on the undried portions. It is not necessary, as a rule, to dry samples of fertilizers in an inert atmosphere, such as hydrogen or carbon dioxid. Drying in vacuo may be practiced when it is desired to secure a speedy desiccation or one at a low temperature.

17. Official Methods.—The Official Agricultural Chemists direct, in the case of potash salts, sodium nitrate, and ammonium sulfate, to heat from one to five grams in a flat platinum or aluminum dish at 130° until the weight is constant.[9] The loss in weight is taken to represent the water. In all other cases heat two grams, or five grams if the sample be very coarse, for five hours in a steam-bath.

In the German stations in the case of untreated phosphates and bone-black the moisture is estimated at from 105° to 110°. Samples which lose ammonia should have the weight of ammonia given off at that temperature, determined separately.

For purposes of comparison it would be far better to have all contents of moisture determined at the boiling-point of water. While this varies with the altitude and barometric pressure yet it is quite certain that the loss on drying to constant weight at all altitudes is practically the same. Where the atmospheric pressure is diminished for any cause the water escapes all the more easily. This, practically, is a complete compensation for the diminished temperature at which water boils.

Where the samples contain no ingredient capable of attacking aluminum, they can be conveniently dried, in circular dishes of this metal about seven centimeters in diameter and one centimeter deep, to constant weight, at the temperature of boiling water.

18. Moisture in Monocalcium Phosphates.—In certain fertilizers, especially superphosphates, containing the monocalcium salt, the estimation of water is a matter of extreme difficulty on account of the presence of free acids and of progressive changes in the sample due to different degrees of heat.

Stoklasa has studied these changes and reaches the following results[10]:

A chemically pure monocalcium phosphate of the following composition, viz.,

was subjected to progressive dryings. The loss of water after ten hours was 1.83 per cent; after twenty hours, 2.46 per cent; after thirty hours, 5.21 per cent; after forty hours, 6.32 per cent; after fifty hours, 6.43 per cent. This loss of water remained constant at 6.43 per cent. This loss represents one molecule of water as compared with the total molecular magnitude of the mass treated. A calcium phosphate, therefore, of the following composition, CaH₄(PO₄)₂·H₂O loses, after forty hours, drying at 100°, its water of crystallization. The calcium phosphate produced by this method forms opaque crystals which are not hygroscopic and which give, on analysis, the following numbers:

The temperature can be raised to 105° without marked change. If the temperature be raised to 200° the decomposition of the molecule is hastened according to the following formula:

4 CaH₄(PO₄)₂ = Ca₂P₂O₇ + Ca(PO₃)₂ + CaH₂P₂O₇ + 2 H₃PO₄ + 4 H₂O.

The chemical changes during the drying of monocalcium phosphates can be represented as follows, temperature 200° for one hour:

8[CaH₄(PO₄)₂·H₂O] = 4CaH₄(PO₄)₂ + Ca(PO₃)₂ + Ca₂P₂O₇
 + CaH₂P₂O₇ + 2H₃PO₄ + 12H₂O.

The further drying at 200° produces the following decomposition:

4CaH₄(PO₄)₂ + Ca(PO₃)₂ + Ca₂P₂O₇ + CaH₂P₂O₇ + 2H₃PO₄
= 2Ca(PO₃)₂ + 4CaH₂P₂O₇ + Ca₂P₂O₇ + 2H₃PO₄ + 5H₂O.

2Ca(PO₃)₂ + 4CaH₂P₂O₇ + Ca₂PO₇ + 2H₃PO₄
= 6Ca(PO₃)₂ + 2CaH₂P₂O₇ + 5H₂O.

Finally, pyrophosphate at 210° is completely decomposed into metaphosphate and water according to the following formula:

6Ca(PO₃)₂ + 2CaH₂P₂O₇ = 8Ca(PO₃)₂ + 2H₂O.

Provided the drying is made at once at 210° the sum of the changes produced as indicated above, can be represented by the following formula:

8[CaH₄(PO₄)₂·H₂O] = 8Ca(PO₃)₂ + 24H₂O.

COMPLETE ANALYSIS OF
MINERAL PHOSPHATES.

19. Constituents to be Determined.—The most important point in the analysis of mineral phosphates is to determine their content of phosphoric acid. Of equal scientific interest, however, and often of great commercial importance is the determination of the percentage of other acids and bases present. The analyst is often called on, in the examination of these bodies, to make known the content of water both free and combined, of organic and volatile matter, of carbon dioxid, sulfur, chlorin, fluorin, silica, iron, alumina, calcium, manganese, magnesia, and the alkalies. The estimation of some of these bodies presents problems of considerable difficulty, and it would be vain to suppose that the best possible methods are now known. Especially is this the case with the processes which relate to the estimation of the fluorin, silica, iron, alumina, and lime. The phosphoric acid, however, which is the chief constituent from a commercial point of view, it is believed, can now be determined with a high degree of precision. Often the estimation of some of the less important constituents is of great interest in determining the origin of the deposits, especially in the case of fluorin. While the merchant is content with knowing the percentage of phosphoric acid and the manufacturer asks in addition only some knowledge of the quantity of iron, alumina, and lime the analyst in most cases is only content with a complete knowledge of the constitution of the sample at his disposal.

20. Direct Estimation of the Phosphoric Acid.—It often happens, in the case of a mineral phosphate, that the only determination desired is of the phosphoric acid. In this instance the analyst may proceed as follows: If the qualitative test shows the usual amount of phosphoric acid, two grams of the sample passed through a sieve, with a millimeter mesh, are placed in a beaker and thoroughly moistened with water. The addition of water is to secure an even action of the hydrochloric acid on the carbonates present. The beaker is covered with a watch-glass and a little hydrochloric acid is added from time to time until all effervescence has ceased. There are then added about thirty cubic centimeters of aqua regia and the mixture raised to the boiling-point on a sand-bath or over a lamp. The heating is continued until chlorin is no longer given off and solution is complete. The volume of the solution is then made up to 200 cubic centimeters without filtering, filtered, and an aliquot part of the filtrate, usually fifty cubic centimeters, representing half a gram of the original sample, taken for the determination of the phosphoric acid according to the method of the Official Agricultural Chemists. The small quantity of insoluble material does not introduce any appreciable error into the process when the volume is made up to 200 or 250 cubic centimeters.

21. Method of the Official Agricultural Chemists for Total Phosphoric Acid.—To the hot solution, for every decigram of phosphorus pentoxid which may be present, add fifty cubic centimeters of the molybdic solution. Digest at 65° for an hour, filter, and wash with water or ammonium nitrate solution[11]. Test the filtrate by renewed digestion with additional molybdate reagent. Dissolve the precipitate on the filter with ammonia in hot water and wash into a beaker, making the volume of filtrate and washings not more than 100 cubic centimeters. Nearly neutralize with hydrochloric acid, cool, and add magnesia mixture from a burette at the rate of about one drop a second, stirring vigorously, meanwhile. The quantity of magnesia mixture to be added is not prescribed in the official method but it should always be in excess of the amount necessary for complete precipitation. For each decigram of phosphorus pentoxid, from eight to ten cubic centimeters should be used. Fifteen minutes after the last of the magnesia mixture has been stirred in, thirty cubic centimeters of ammonia of 0.95 specific gravity are added and the beaker set aside for two hours or longer. The ammonium magnesium phosphate is separated by filtration, dried, ignited gently at first, and finally over a blast-lamp and weighed as magnesium pyrophosphate. The factors for calculating the phosphorus pentoxid and tricalcium phosphate from the weight of pyrophosphate are given below on the two bases; viz., hydrogen equals 1, and oxygen equals 16.

H = 1.
Mg₂P₂O₇ × 0.63976 = P₂O₅
Mg₂P₂O₇ × 1.3964  = Ca₃(PO₄)₂
P₂O₅ × 2.1827  = Ca₃(PO₄)₂

O = 16.
Mg₂P₂O₇ × 0.63792 = P₂O₅
Mg₂P₂O₇ × 1.3926  = Ca₃(PO₄)₂
P₂O₅ × 2.1831  = Ca₃(PO₄)₂

22. Preparation of Solutions.—Molybdic Solution.—Dissolve 100 grams of molybdic acid in 400 grams or 417 cubic centimeters of ammonia, of 0.96 specific gravity, and pour the solution thus obtained into 1,500 grams or 1,250 cubic centimeters of nitric acid, of 1.20 specific gravity. Keep the mixture in a warm place for several days, or until a portion heated to 40° deposits no yellow precipitate of ammonium phosphomolybdate. Decant the solution from any sediment and preserve in glass-stoppered vessels.

Magnesia Mixture.—Dissolve twenty-two grams of recently ignited calcined magnesia in dilute hydrochloric acid, avoiding an excess of the latter. Add a little calcined magnesia in excess, and boil a few minutes to precipitate iron, alumina, and phosphoric acid; filter, add 280 grams of ammonium chlorid, 700 cubic centimeters of ammonia of specific gravity 0.96, and water enough to make a volume of two liters. Instead of the solution of twenty-two grams of calcined magnesia, 110 grams of crystallized magnesium chlorid may be used.

Dilute Ammonia for Washing.—One volume of ammonia, of 0.96 specific gravity, mixed with three volumes of water, or usually one volume of concentrated ammonia with six volumes of water.

23. Use of Tartaric Acid in Phosphoric Acid Estimation.—In the presence of iron the molybdate mixture is likely to carry down some ferric oxid with the yellow precipitate. To prevent this, and also hinder the separation of molybdic acid in the solution on long standing, tartaric acid has been recommended.

Jüptner has found that the presence of tartaric acid does not interfere with the separation of the yellow precipitate, as some authorities assert.[12] Even 100 grams of the acid in one liter of molybdate solution produce no disturbing effect. Molybdate solution treated with tartaric acid did not show any separation of molybdic acid when kept for a year at room temperatures. The presence of tartaric acid, therefore, is highly recommended by him to prevent the danger of obtaining both ferric oxid and molybdic acid with the yellow precipitate.

24. Water and Organic Matters.—The sample, according to the practice of Chatard, should be ground fine enough to leave no residue on an eighty mesh sieve, and should be thoroughly mixed by passing it three times through a forty mesh sieve[13].

Two grams are weighed into a tared platinum crucible. This, with its lid, is placed in an air-bath at 105°, and heated for at least three hours. The lid is then put on, and the crucible is placed in a desiccator and weighed as soon as cold. The loss in weight is the moisture.

Wyatt recommends that two grams of the fine material be heated in ground watch-glasses, the edges of which are separated so as to allow the escape of the moisture.[14] The heating is continued for three hours at 110°, the watch-glasses then closed and held by the clip, cooled in a desiccator, and weighed. This method is excellent for very hygroscopic bodies, but where quick-acting balances are used, scarcely necessary for a powdered mineral.

The residue from the moisture determination is gradually heated to full redness over a bunsen, and then ignited over the blast-lamp. This operation is repeated after weighing until a constant weight is obtained. The loss (after deducting the percentage of carbon dioxid as found in another portion) may be taken as water and organic matter. This method is sufficient for all practical purposes; but when minerals containing fluorin are strongly ignited, a part of the fluorin is expelled; hence, if more accurate determinations are required, the loss of fluorin must be taken into account. In this laboratory it has been proved that a pure calcium fluorid undergoes progressive decomposition at a bright red heat with formation of lime.

Wyatt directs that the combined water and organic matters be determined in the residue from the moisture estimation as follows: The residue is brushed into a weighed platinum crucible, which is heated over a small bunsen for ten minutes and then brought to full heat of a blast-lamp for five minutes. After cooling, the total loss is determined by weighing. After deducting the carbon dioxid determined in a separate portion, the residual loss is regarded as due to combined moisture and organic matter.

25. Carbon Dioxid.—Many forms of compact apparatus have been devised for this estimation, but none of them is satisfactory if accurate results are desired.[15] Not to mention other objections, many phosphates must be heated nearly to the boiling-point with dilute acid to effect complete decomposition of the carbonates. The distillation method described by Gooch[16] is excellent, and when once the apparatus is set up, its work will be found to be rapid and satisfactory.

Wyatt regards the estimation of carbon dioxid as one of the most important for factory use. The carbonates present in a sample indicate the loss of an equivalent amount of acid in the process of conversion into superphosphate.[17]

The apparatus employed for estimating carbon dioxid may be any one of those in ordinary use for this purpose. The principle of the process depends on the liberation of the gas with a mineral acid, its proper desiccation, and subsequent absorption by a caustic alkali, best in solution.

The apparatus of Knorr, described in volume first, page 338, may be conveniently used. The weight of the sample to be used should be regulated by the content of carbonate. When this is very high, from one to two grams will be found sufficient; when low, a larger quantity must be used. Hydrochloric is preferred as the solvent acid. Those forms of apparatus which are weighed as a whole and the carbon dioxid determined by reweighing after its expulsion, are not as reliable as the absorption apparatus mentioned.

26. Soluble and Insoluble Matter.—Five grams of the fine phosphate are put into a beaker, twenty-five cubic centimeters of nitric acid, (specific gravity 1.20) and 12.5 cubic centimeters of hydrochloric acid (specific gravity 1.12) are added. The beaker, covered with a watch-glass, is placed upon the water-bath for thirty minutes[18]. The contents of the beaker are well stirred from time to time, and at the end of the period the beaker is removed from the bath, filled with cold water, well stirred, and allowed to settle. The solution is next filtered into a half liter flask, and the residue is thoroughly washed with cold water, partially dried, and then ignited, (finishing with the blast-lamp) and brought to constant weight. The figures thus obtained will, however, be incorrect, because the fluorin liberated during the solution of the phosphates dissolves a portion of the silica. Hence, the results are too low. Nevertheless, as the same action would occur in the manufacture of a superphosphate from the material, the determination may be considered, as a fair approximation to commercial practice. The ignited residue must be tested for phosphorus pentoxid.

27. Preparation of the Solution.—The flask containing the filtrate is filled to the mark with cold water, and the solution is thoroughly mixed by twice pouring into a dry beaker and returning it to the flask. Cold water is used for washing the residue, since if hot water be used, the sesquichlorids are apt to become basic and insoluble, and hence to remain in the residue and on the filter paper. Besides, as the flask is to be filled to the mark, the contents must be cold before any volumetric measurements can be made.

28. Silica and Insoluble Bodies.—Wyatt describes the following method for determining the total insoluble or siliceous matters in a mineral phosphate[19]. Five grams of the fine sample are placed in a porcelain dish with about thirty cubic centimeters of aqua regia. The dish is covered with a funnel, placed on a sand-bath and, after solution is complete, evaporated to dryness with care to prevent sputtering. When dry the residue is moistened with hydrochloric acid and again dried, rubbing meanwhile to a fine powder. The heat of the bath is then increased to 125° and maintained at this temperature for about ten minutes. When cool, the residue is treated with fifty cubic centimeters of hydrochloric acid for fifteen minutes. The acid is then diluted and filtered on a gooch, which is washed with hot water until the filtrate amounts to a quarter of a liter. The residue in the crucible is dried, ignited, and weighed. This method, unless the solution be subsequently boiled with nitric acid, may not retain all the phosphoric acid in the ortho form.

It is difficult to estimate the total silica by the ordinary methods of mineral analysis. This is due to the fact that in an acid solution of a substance containing silicates and fluorids the whole of the silica or the fluorin, as the case may be may escape as silicofluorid on evaporation. Again, it is not easy to decompose calcium phosphate by fusing with sodium carbonate. If an attempt be made to do this, however, the process should be conducted as follows: A portion of the sample is ground to an impalpable powder in an agate mortar. From one to two grams of the substance are mixed with five times its weight of sodium carbonate and fused with the precautions given in standard works on quantitative analysis. The fused mass is digested in water, boiled, and filtered, and the residue washed first with boiling water and afterwards with ammonium carbonate. The filtrate contains all the fluorin as sodium fluorid and, in addition to this, sodium carbonate, silicate, and aluminate. Mix the filtrate with ammonium carbonate and heat for some time, replacing the ammonium carbonate which evaporates. Separate by filtration the silicic acid hydrate and aluminum hydroxid which are formed and wash them with ammonium carbonate. To separate the last portions of silica from the filtrate, add a solution of zinc oxid in ammonia. Evaporate until no more ammonia escapes and separate, by filtration, the zinc silicate and oxid. Determine the silica in this precipitate by dissolving in nitric acid, evaporating to dryness, taking up with nitric acid and separating the undissolved silica by filtration. In the alkaline filtrate the fluorin may be estimated by the usual method as calcium salt.

29. Estimation of Lime.—One hundred cubic centimeters of the solution (containing one gram of the original substance) are evaporated in a beaker to about fifty cubic centimeters; ten cubic centimeters of dilute sulfuric acid (one to five) are added; and the evaporation is continued on the water-bath until a considerable crop of crystals of gypsum has formed[20]. The solution is then allowed to cool, when it generally becomes pasty, owing to the separation of additional gypsum. When it is cold, 150 cubic centimeters of ninety-five per cent alcohol are slowly added, with continual stirring, and the whole is allowed to stand for three hours, being stirred from time to time. After three hours, it is filtered, with the aid of a filter-pump, into a distillation flask, and the beautifully crystalline precipitate, which does not adhere to the beaker, is washed with ninety-five per cent alcohol. The filter, with the precipitate, is gently removed from the funnel and inverted into a platinum crucible, so that, by squeezing the point of the filter, the precipitate is made to fall into the crucible, and the paper can be pressed down smoothly upon it. On gentle heating of the crucible, the remaining alcohol burns off, and when the paper has been completely destroyed, the heat is raised to the full power of a bunsen for about five minutes. After cooling in a desiccator the crucible containing the calcium sulfate, is weighed. The filtration may also be accomplished on asbestos felt.

30. The Ammonium Oxalate Method.—This method has been extensively used in this country in commercial work, and is best carried out as described by Wyatt.[21] The total filtrates from the iron and alumina precipitates, secured as described in paragraph 33, are well mixed and concentrated to a volume of about 100 cubic centimeters. There are added about twenty cubic centimeters of a saturated solution of ammonium oxalate, and after stirring, the mixture is allowed to cool and remain at rest for six hours. The supernatant liquid is poured through a filter, the residue washed three times by decantation with hot water and brought upon the filter. The beaker and precipitate are washed at least three times. The precipitate is dried and ignited at low redness for ten minutes. The temperature is then raised by a blast and the ignition continued for five minutes longer, or until the lime is obtained as oxid. The precipitate is likely to contain magnesia. The magnesia is estimated in the filtrates from the lime determination by first mixing them and concentrating to 100 cubic centimeters, which, after cooling, are made strongly alkaline with ammonia. After allowing to stand for twelve hours the ammonium magnesium phosphate is collected and reduced to magnesium pyrophosphate by the usual processes. If one gram of the original material has been used the pyrophosphate obtained, multiplied by 0.36, will give the weight of magnesia contained therein.

31. Lime Method of Immendorff.—The tedious processes required to determine the lime in the presence of iron, alumina, and large quantities of phosphoric acid are well known to analysts. Immendorff has published a method, accompanied by the necessary experimental data, based on the comparative insolubility of calcium oxalate in very dilute solution of hydrochloric acid. He has shown in the data given that the lime is all precipitated in the conditions named and that the precipitate, when properly prepared, is not contaminated with weighable amounts of the other substances found in the original solution[22]. The ease with which oxalic acid can be determined volumetrically with potassium permanganate solution aids greatly in the time-saving advantages of the process.

In a hydrochloric acid solution of a mineral phosphate an aliquot part of the filtrate representing about 250 milligrams of calcium oxid, usually about twenty-five cubic centimeters, should be taken for the analysis. Ammonia is added in slight excess and then the acid reaction restored with hydrochloric until shown plainly by litmus. The solution is then heated and the lime thrown down by adding a solution of ammonium oxalate in excess. In order to secure a greater dilution of the hydrochloric acid after the precipitation has been made, water should be added until the volume is half a liter. Before filtering, the whole should be cooled to room temperature. The precipitate should be washed first with cold and afterwards with warm water. The well-washed precipitate is dissolved in hot dilute sulfuric acid and the solution, while hot, titrated with a standard solution of potassium permanganate set by a solution of ammonio-ferrous sulfate.

If one cubic centimeter of the permanganate represent 0.005 gram of iron it will correspond almost exactly to 0.0035 gram of calcium oxid.