Chapter XIII: Part 13

The most concentrated aqueous acid has a specific gravity of 1.65, is colorless, fumes slightly when exposed to the air, and boils at 200°. It has no odor, possesses an oily consistence and has a strong and agreeably acid taste. It reddens litmus without bleaching it and is slowly volatilized at 138° without decomposition. It is unaffected by exposure to the light, even the sun’s rays. It is not decomposed by hydrosulfuric, sulfurous, or hydrochloric acids, nor by alcohol. Paper saturated with the strong acid does not take fire spontaneously, but it deflagrates with red-hot charcoal.

The acid prepared by the method of Kreider has approximately the composition of the di-hydrate, HClO₄·2H₂O.[229] Unless well evaporated, however, it is a little more dilute than is shown by the above formula. The di-hydrate is quite stable and the more dilute acid can be kept for an indefinite time. Kreider has kept the acid for six months and noticed no change whatever in its composition. Acid containing one gram of perchloric acid in a cubic centimeter has been kept three months with perfect safety. There is no reason why the strong aqueous acid should not be made a regular article of commerce by dealers in chemical supplies, under proper restrictions for storage and transportation.

The strong acid made in this laboratory by the Kreider method has not given the least indication of easy or spontaneous decomposition.

=274. The Analytical Process.=—The perchlorate process cannot be applied in the presence of sulfuric acid or dissolved sulfates. This acid, when present, is to be removed by the usual methods before applying the perchloric acid. Phosphoric acid may be present, but in this case a considerable excess of the reagent must be used. The process, as originally proposed by Caspari and carried out by Kreider, is as follows:[230]

The substance, free from sulfuric acid, is evaporated for the expulsion of free hydrochloric acid, the residue stirred with twenty cubic centimeters of hot water and then treated with perchloric acid, in quantity not less than one and one-half times that required by the bases present, when it is evaporated, with frequent stirring, to a thick, sirup-like consistency, again dissolved in hot water and evaporated, with continued stirring, till all hydrochloric acid has been expelled and the fumes of perchloric acid appear. Further loss of perchloric acid is to be compensated for by addition of more. The cold mass is then well stirred with about twenty cubic centimeters of wash alcohol—ninety-seven per cent alcohol containing two-tenths per cent by weight of pure perchloric acid, with precautions against reducing the potassium perchlorate crystals to too fine a powder. After settling, the alcohol is decanted on the asbestos filter and the residue similarly treated with about the same amount of wash alcohol, settled, and again decanted. The residual salt is then deprived of alcohol by gently heating, dissolved in ten cubic centimeters of hot water and a little perchloric acid, when it is evaporated once more, with stirring, until fumes of perchloric acid rise. It is then washed with one cubic centimeter of wash alcohol, transferred to the asbestos, preferably by a policeman to avoid excessive use of alcohol, and covered finally with pure alcohol; the whole wash process requiring from about fifty to seventy cubic centimeters of alcohol. It is then dried at about 130° and weighed.

The substitution of a gooch for the truncated pipette employed by Caspari will be found advantageous; and asbestos capable of forming a close, compact felt should be selected, inasmuch as the perchlorate is in part unavoidably reduced, during the necessary stirring, to so fine a condition that it tends to run through the filter when under pressure. A special felt of an excellent quality of asbestos was prepared for the determinations given below and seemed to hold the finer particles of the perchlorate very satisfactorily.

A number of determinations made of potassium, unmixed with other bases or non-volatile acids, is recorded in the following table:

Potassium Potassium Error on Error on
chlorid Volume of perchlorate potassium potassium Error on
taken. filtrate. found. perchlorate. chlorid. potash.

Cubic
Grams. centimeters. Grams. Grams. Grams. Grams.
0.1000 54 0.1851 0.0008— 0.0004— 0.0003—
0.1000 58 0.1854 0.0005— 0.0002— 0.0002—
0.1000 51 0.1859 0.0000 0.0000 0.0000
0.1000 50 0.1854 0.0005— 0.0002— 0.0002—
0.1000 48 0.1859 0.0000 0.0000 0.0000
0.1000 52 0.1854 0.0005— 0.0002— 0.0002—

Considerable difficulty, however, was experienced in obtaining satisfactory determinations of potassium associated with sulfuric and phosphoric acids. As Caspari has pointed out, the sulfuric acid must be removed by precipitation as barium sulfate before the treatment with perchloric acid is attempted, and unless the precipitation is made in a strongly acid solution, some potassium is carried down with the barium. Phosphoric acid need not be previously removed, but to secure a nearly complete separation of this acid from the potassium, a considerable excess of perchloric acid should be left upon the potassium perchlorate before it is treated with the alcohol. When these conditions are carefully complied with, fairly good results may justly be expected. Below is given a number of the results obtained:

(A) = Volume of filtrate. Cubic centimeters.
(B) = Potassium perchlorate found.
(C) = Error on potassium perchlorate.
(D) = Error on potassium chlorid.
(E) = Error on potassium potash.

Compounds taken. (A) (B) (C) (D) (E)
Grams. Grams. Grams. Grams. Grams.
Potassium chlorid = 0.10
Calcium carbonate = 0.13 50 0.1887 0.0027+ 0.0014+ 0.0005+[231]
Magnesium sulfate = 0.13 82 0.1875 0.0016+ 0.0008+ 0.0005+[232]
Ferric chlorid = 0.05 80 0.1861 0.0002+ 0.0001+ 0.0001+[233]
Magnesium sulfate = 0.05 80 0.1843 0.0016- 0.0008- 0.0005-[234]
Manganese dioxid = 0.05 92 0.1839 0.0020- 0.0010- 0.0006-[235]
Sodium phosphate = 0.40 60 0.1854 0.0005- 0.0002- 0.0002-[236]

In the last three experiments of the above table the amount of perchloric acid was about three times that required to unite with the bases present, and the phosphoric acid subsequently found with the potassium was hardly enough to appreciably affect the weight, although its absolute removal was found impossible.

That the magnesia does not produce any disturbing effect, as is supposed by the French chemists, Kreider has proved by the following test: One hundred and fifty milligrams of magnesium carbonate were treated with perchloric acid, evaporated till fumes of perchloric acid appeared, and cooled, when the magnesium perchlorate crystallized: But on treating it with about fifteen cubic centimeters of ninety-seven per cent alcohol containing two-tenths per cent of perchloric acid a perfectly clear solution was obtained. If, therefore, a sufficient excess of acid be used, no interference will be caused by the presence of magnesium.

While it is true, therefore, that the potassium perchlorate obtained may be contaminated with a trace of phosphoric acid, if the latter be present in large quantity, no fear of contamination with magnesia need be entertained if a sufficient quantity of the perchloric acid be used.

=275. Removal of the Sulfuric Acid.=—The practical objection to the removal of the sulfuric acid in the form of barium sulfate rests on the fact of the mechanical entanglement of some of the potash in the barium salt. Unless special precautions are taken, therefore, a considerable amount of the potash will be found with the barium sulfate.

Caspari has succeeded in reducing this amount to a minimum by the following procedure:[237] The solution of barium chlorid is prepared by dissolving 127 grams of crystallized barium chlorid in water, adding 125 cubic centimeters of thirty-five per cent hydrochloric acid, and bringing the total volume up to one liter with water.

Five grams of the substance from which the sulfuric acid is to be removed are boiled with 150 cubic centimeters of water and twenty of strong hydrochloric acid. While the solution is still in ebullition it is treated, drop by drop with constant stirring, with the barium chlorid solution above mentioned, until a slight excess is added. This excess does not cause any inconvenience subsequently. After the precipitation is complete the boiling is continued for a few minutes, the mixture cooled and made up to a quarter of a liter with water. No account is taken of the volume of the barium sulfate formed since, even with the precautions mentioned, a little potassium is thrown down and the volume of the barium sulfate tends to correct this error. With a solution from which the sulfuric acid had been removed as above indicated, Caspari found a loss of only one milligram of potassium perchlorate in a precipitate weighing over 800 milligrams.

=276. Applicability of the Process.=—Experience has shown that sulfuric acid is the only substance which need be removed from ordinary fertilizers preparatory to the estimation of the potash by means of perchloric acid. The fact that this process can be used in the presence of phosphoric acid is a matter of great importance in the estimation of potash in fertilizers, inasmuch as these fertilizers nearly always contain that acid. The fact that the French chemists noticed that magnesia was a disturbing element in the process, as has been indicated in volume first, probably arose from its presence as sulfate. Neither Caspari nor Kreider has noticed any disturbance in the results which can be traced to the presence of magnesia as a base.

If ammonia be present, however, there is a tendency to the production of ammonium perchlorate which is somewhat insoluble in the alcohol wash used. Solutions therefore containing ammonia before treating by the perchlorate method for potash should be rendered alkaline by soda-lye and boiled. With the precautions above mentioned, the method promises to prove of great value in agricultural analysis, effecting both a saving of time and expense in potash determinations.

=277. Accuracy of the Process.=—The perchlorate was tried in conjunction with the platinum method on the two samples of potash fertilizer prepared and distributed by the official reporter on potash for 1893.[238] One of the samples was of a fertilizer which had been compounded for the Florida trade and contained bone, dried blood, and potash, mostly in the form of sulfate. The other sample consisted of mixed potash salts, sulfate, chlorid, double salt, kainit, and about five per cent of the triple sulfate of calcium, potassium, and magnesium.

The results obtained by Wagner and Caspari on the two samples follow:

Sample No. 1. Sample No. 2.
Per cent potash. Per cent potash.
By the platinum method 13.25 37.98
By the perchlorate method 13.09 37.82

The perchlorate method on the whole appears to be quite as accurate as the platinum process, requires less manipulation and can be completed in a shorter time and at less expense for reagents.

AUTHORITIES CITED IN PART THIRD.

[185] Connecticut Agricultural Experiment Station, Bulletin No. 97, p. 7.

[186] Annual Report Connecticut Station, 1892, p. 32.

[187] Colorado Agricultural Experiment Station, Bulletin No. 10.

[188] Connecticut Agricultural Experiment Station, Bulletin No. 103, p. 9.

[189] Annual Report, Massachusetts Agricultural Experiment Station, 1888, p. 202.

[190] Vid. op. cit. 2, 1890, p. 110.

[191] Traité de la Fabrication de Sucre, Horsin-Déon, p. 511.

[192] Chemical Division, U. S. Department of Agriculture, Bulletin No. 37, p. 350.

[193] Journal of the American Chemical Society, Vol. 17, p. 86.

[194] Volume First, pp. 19, et seq.

[195] Precht: Die Stassfurter Kalisalze.

[196] Maercker: Die Kalidüngung, S. 1.

[197] Vid. op. cit. supra, p. 3.

[198] Vid. op. cit. 12, p. 5.

[199] Vid. op. cit. 12, p. 7.

[200] Volume First, pp. 378, et seq.

[201] Chemical News, Vol. 44, pp. 77, 86, 97, and 129.

[202] Chemical Division, U. S. Department of Agriculture, Bulletin No. 7, p. 38.

[203] Vid. supra, Bulletin No. 43, p. 349.

[204] Die Agricultur-Chemische Versuchs-Station, Halle a/S., S. 76.

[205] Methoden van onderzock aan de Rijkslandbouw-proefstations, 1893, p. 7.

[206] From the Official Swedish Methods. Translated for the Author by F. W. Woll.

[207] Chemical Division, U. S. Department of Agriculture, Bulletin No. 35, p. 63.

[208] Chemiker Zeitung, Band 18, S. 1320.

[209] Journal of the American Chemical Society, Vol. 17, p. 85.

[210] Chemical Division, U. S. Department of Agriculture, Bulletin No. 43, p. 26.

[211] Vid. op. cit. 25, Vol. 17, p. 46.

[212] Zeitschrift für angewandte Chemie, 1891, S. 281.

[213] Zeitschrift für analytische Chemie, Band 32, S. 184.

[214] Vid. op. cit. 25, Vol. 16, p. 364.

[215] Vid. op. cit. 25, Vol. 17, p. 463.

[216] Vid. op. et. loc. cit. supra.

[217] Chemiker Zeitung, 1890, S. 1246.

[218] Volume First, pp. 369, 375.

[219] Annales de Chimie et de Physique {2}, Tome 46, p. 294.

[220] Comptes rendus, Tome 73, p. 1296.

[221] Zeitschrift für analytische Chemie, Band 14, S. 152.

[222] Chemical News, Vol. 44, p. 316.

[223] Rapport adressé par la Comité des Stations Agronomiques, 1887, p. 10.

[224] Zeitschrift für angewandte Chemie, 1891, S. 691.

[225] Vid. op. cit. supra, 1892, S. 233.

[226] Vid. op. cit. 40, 1893, S. 68.

[227] American Journal of Science, June, 1895, from advance proofs sent by author.

[228] Watt’s Translation, Vol. 2, pp. 317-318.

[229] Manuscript communication from Mr. Kreider.

[230] Vid. op. et loc. cit. 43.

[231] The residue showed phosphoric acid plainly when tested.

[232] The residue showed phosphoric acid plainly when tested.

[233] Only traces of phosphoric acid found in the residue.

[234] Only traces of phosphoric acid found in the residue.

[235] Only traces of phosphoric acid found in the residue.

[236] Only traces of phosphoric acid found in the residue.

[237] Zeitschrift für angewandte Chemie, 1893, S. 73.

[238] Chemical Division, U. S. Department of Agriculture, Bulletin No. 38, p. 57.

PART FOURTH.

MISCELLANEOUS FERTILIZERS.

=278. Classification.=—Nitrogen, phosphoric acid, and potash are the most important of the plant foods both from a commercial and physiological point of view. They are the chief constituents of the most important fertilizers and manures, but are by no means the sole essential elements of plant nutrition. Lime, magnesia, soda, sulfur, chlorin, and many other elements are found constantly in plants and must be regarded as normal constituents thereof. It is the purpose here, however, to speak only of those substances which are used as fertilizers and which constantly or occasionally are subjected to chemical examination for determining their commercial or agronomic value. These bodies may be conveniently divided into two classes; _viz._, mineral and organic. Among those of mineral nature may be mentioned lime, gypsum, marls, wood-ashes, common salt, and ferrous sulfate; among those of organic nature may be included guano, hen manure, stall manure, composts, and muck.

=279. Forms of Lime.=—By the term lime is meant the product obtained by subjecting limestone or other lime carbonates to the action of heat until the carbon dioxid contained therein is expelled. The resulting lime, CaO, when exposed for some time to the air, or at once on the addition of water, is converted into the hydrate CaO₂H₂, known as slaked lime. On longer exposure to the air, the hydrate gradually absorbs carbon dioxid and becomes converted into carbonate. In whatever form, therefore, lime is applied to the soil, it is found in the end, as carbonate. A distinction should also be made between lime obtained from mineral substances and that got from organic products such as shells. Strictly speaking this is not a definite matter, inasmuch as limestones are sometimes but little more than aggregations of fossil shells. Practically, however, the distinction is made, and some farmers prefer shell lime to that of any other kind. Gas lime, that is lime which has been used for the purification of illuminating gas made from coal, is hardly to be considered in this connection, since it may contain very little even of the hydrate. In this case the lime has been converted largely into carbonate and sulfid.

=280. Application of Lime.=—For many reasons it is important that the lime be transported to the field before it has had time to be converted into hydrate. The transportation costs less in this state and it can be handled with far less inconvenience than when slaked. The lime should be placed in small piles and left thus, best covered with a little earth, until thoroughly slaked. It is then spread evenly over the surface. The quantity used per acre depends largely on the nature of the soil. Stiff clays and sour marsh lands require a larger dressing than loams or well aerated soils. From three to six thousand pounds per acre are the quantities usually employed. When the lime is once thoroughly incorporated in the soil it is rapidly converted into carbonate, but while in the caustic state it may act vigorously in promoting the decay of organic matter and may prove injurious in promoting the decomposition of ammonium salts with attendant loss of nitrogen.

=281. Action of Lime.=—The benefits arising from the application of lime to agricultural lands, although in many cases great, do not arise from any distinct fertilizing action of its own. Plants need lime for growth and need plenty of it, but as a rule any soil which is good enough to grow crops will contain enough lime to furnish that constituent of the crops for many years. Its action is both mechanical and chemical. By virtue of the latter property it renders available for plant food bodies already existing in the soil but existing in such shape as to be unavailable for plants. The supply of plant food available for the crops of one year is increased but this increase is at the expense of the following years. Lime is a stimulant. There is an European proverb that “lime enriches the father but beggars the son.” Nevertheless, a limestone country is usually a fertile one and soils containing plenty of lime naturally, are nearly always rich soils. It is said that the trees and plants which farmers pick out as indicative of rich land are nearly always those which prefer lime soils.

The mechanical action of lime on soils tends to lighten heavy clays and loams and to render firmer and more consistent the light and shifting sandy soils. When a lump of clay is stirred up in a bucket of rain water the water becomes muddy and remains that way for many days. If, however, to the bucket of muddy water a little lime water be added the suspended particles of clay begin to flocculate and soon the water is clear and the clay falls to the bottom, nor does it again make the water muddy for a long time when stirred up with it. The flocky character of the precipitate is tenaciously retained and it is necessary to knead the clay for some time to induce it to reassume its original heavy character. An action like this takes place when lime is added to heavy soils so that the soil becomes more porous and assumes a better tilth on plowing. With sandy soils an altogether different action takes place. In making mortar, as is well known, sand is stirred in with milk of lime and after being exposed to air for a while the mixture becomes hard and firm, the firmness increasing with age. This is due to the fact that when the mortar dries the lime begins to absorb carbon dioxid from the air and is converted into grains of carbonate which adhere strongly to neighboring sand grains and to each other so that the whole soon gets to be a solid mass. Something like this takes place in the soil and the sand grains are to some extent bound together. The increased firmness of the soil thus gained is often of considerable advantage.

Besides these actions, which are more or less mechanical, lime exerts a chemical action on many soil constituents. Feldspar and other common rocks contain potash, and this potash is in such a form as to be inaccessible to plants. These rocks exist in the shape of small particles in many soils and on them lime exerts a decomposing action, setting the potash free. Lime also hastens the decomposition of the nitrogenous organic matter and at the same time renders the soil more retentive of the products formed. The conversion of ammonia, resulting from the decomposition of such organic matter into nitrites and nitrates, is not easily accomplished without a proper amount of calcium carbonate. The microorganisms producing this change, which is known as nitrification, apparently require its presence for neutralizing the acid formed. In general, it may be said that the presence of lime hastens the putrefactive process. This is the reason it is so largely used in making composts.

It is difficult to say just what soils will be improved by liming and what will not, and it is a matter which must be settled by experiment in each case. As a rule heavy clays and loams are benefited, yet of two such soils, apparently identical, one may not be affected in any marked degree while the other may readily respond to treatment. Sandy soils are often improved but sometimes not. Sour, boggy lands, are usually improved by the addition of enough lime to neutralize their undue acidity. Marsh grasses and plants are more tolerant of acid in the soil than tame grasses are, so that in unlimed soil the former run out the latter. The application of lime alone to a very poor soil does not pay.

The particles of lime resting in the soil are partially dissolved by the next rainfall after application, or by the soil moisture, forming lime water, and the lime is distributed in this form through the soil to some extent. It all probably soon becomes converted into carbonate as ground air is usually quite rich in carbon dioxid. Indeed, for many soils, it is immaterial whether lime be applied as lime or as carbonate, granting, of course, that the latter be ground to a fine powder. Economy is in favor of the lime, however, not only because it needs no grinding, but because it is lighter than the corresponding amount of carbonate, making a saving in transportation. The difference is quite considerable, fifty-six pounds of lime being equivalent in effect to 100 pounds of carbonate. For these reasons as well as because it possesses some valuable properties not shared by the carbonate, it is possible that for most localities lime is to be preferred to any form of ground oyster shells, ground limestone, marble dust or the like.

One of these valuable properties not possessed by limestone, is said to be that of acting as a fungicide and insecticide. As a rule, fungi prefer acid reaction in the substances in which they grow, so that the strongly alkaline properties of lime may make a limed soil unsuitable for their growth.[239]

=282. Analysis of Lime.=—Lime, which is prepared for use as a fertilizer, is rarely submitted to a chemical examination. It is easy to see, however, that such an examination is of some importance. If the real value of a sample be dependent on the content of lime, the actual quantity present as determined by analysis, must fix the value for agricultural purposes. The more important things to be determined are the quantities of lime, and of slaked lime, of undecomposed calcium carbonate, and of insoluble matter. It will be also of interest to determine the respective quantities of lime present as oxid, hydrate, and carbonate. If any question be raised in the case of slaked lime in respect of its origin, it can usually be answered by an examination of the unburned or unslaked residues. In perfectly slaked lime containing no débris, the analyst will be unable to discover whether it has been made from limestone, marble or shells. The lime used for agricultural purposes should be reasonably free of magnesia, and should not be air-slaked before transportation to the field. In dry air-slaking, a considerable quantity of carbonate may be formed.

=283. The Process.=—(1) _Insoluble and Soluble Constituents._—A representative sample of the lime having been secured, it is reduced to a powder and passed through a half millimeter mesh sieve or ground to a fine powder in an agate mortar. Digest two grams of this sample with an excess of hydrochloric acid, for two hours with frequent stirring; filter, wash the residue with hot distilled water until chlorin is all removed, and dry to constant weight. The lime, magnesia, silica, and other constituents of the filtrate, are determined by the usual processes of mineral analysis.[240]

(2) _State of Combination of the Lime._—In a lime containing only small quantities of magnesia the lime carbonate may be determined by estimating the carbon dioxid by any one of the reliable processes in use.[241] In every case sufficient acid must be employed to combine with all the bases present. Tartaric or hydrochloric acid may be used. From the volume or weight of the carbon dioxid obtained the quantity of calcium carbonate may be calculated. Since magnesium carbonate is more easily decomposed by heat than the corresponding calcium compound, any residual carbonate in a well-burned sample is probably lime. The total percentage of lime in the sample is to be determined in the usual way by precipitation as oxalate and weighing as carbonate or oxid. The lime existing as oxid can be determined by exposing a weighed sample in an atmosphere of aqueous vapor until all the lime is slaked. After drying at 100° the increase in weight is determined and the calcium oxid calculated from the formula, CaO + H₂O = CaO₂H₂.

If now the total lime be represented by _a_; the lime combined as carbonate by _b_; and that present as oxid by _c_; the quantity _x_ existing as hydrate may be calculated from the equation

_x_ = _a_ - (_b_ + _c_).

Example: Let the total lime be 88 per cent.
CaO as carbonate, 2 “ “
CaO as oxid, 78 “ “

Then the CaO as hydrate = 88 - (2 + 78) = 8 per cent. The total lime as oxid and hydroxid may also be separated from that present as carbonate by solution in sugar.[242] One gram of calcium oxid is completely soluble in 150 cubic centimeters of a ten per cent sucrose solution. Magnesia, iron and alumina do not interfere with the determinations.

=284. Gypsum or Land Plaster.=—This substance is highly prized as a top dressing for grass and for admixture with stall manure for the purpose of fixing ammonia. Its value in both cases depends upon its percentage of hydrated calcium sulfate. The quantity of gypsum mined in the United States in 1893 was a little over 250,000 tons. Of this amount only about 50,000 tons were used as fertilizer.[243] In the same time there were imported into the United States, in round numbers, 170,000 tons. If the same proportionate part of this were used for fertilizing purposes, it may be said that the annual consumption of land plaster in the United States at the present time for agricultural uses is about 75,000 tons.

Gypsum, being a very soft mineral, is easily ground and should be in the state of a fine powder when used for fertilizing purposes. It is soluble in about 500 parts of rain water, so that when applied as a top dressing it is carried into the soil by rain. Its favorable action is both as a plant food and mechanically in modifying, in an advantageous way, the physical constituents of the soil. It is also valuable for composting and for use in stables by reason of its power of fixing ammonia by the formation of lime carbonate and ammonium sulfate:

(H₄N)₂CO₃ + CaSO₄ = (H₄N)₂SO₄ + CaCO₃.

=285. Analysis of Gypsum.=—For agricultural purposes it will be sufficient to determine the quantity of sulfuric acid, and to calculate therefrom the amount of calcium sulfate in the sample: Or the lime may be determined and the quantity of sulfate calculated therefrom.

(1) _Insoluble Matter._—In the conduct of the work the sample of gypsum is rubbed to an impalpable powder in an agate mortar. The washed sample, about one gram, is dissolved in a large excess of dilute hydrochloric acid, the digestion being continued at near the boiling-point, with frequent stirring, for at least two hours. The solution is made alkaline, filtered, and the residue washed and dried to constant weight.

(2) _Sulfuric Acid._—The washings and filtrate from the above determination are made up to a definite volume with water and divided into two equal parts. The sulfuric acid is estimated in one part by adding to it sodium carbonate until the acidity is nearly neutralized. The sulfuric acid is then thrown down at near boiling temperature by the gradual addition of barium chlorid solution. The barium sulfate formed is separated, washed, dried, and weighed in the usual manner.

(3) _Iron and Alumina._—To the other half of the solution a little nitric acid is added and boiled to convert any ferrous into ferric iron. On the addition of ammonia the iron and alumina are separated as hydroxids, collected on a gooch, washed, dried, ignited, and weighed as oxids.

(4) In the filtrate the lime is thrown out as oxalate, and separated and weighed in the usual way as oxid. One part of CaO is equal to 2.4286 parts of CaSO₄.

(5) _Moisture._—Dry about two grams of the sample to constant weight at 80°.

(6) _Water of Crystallization._—Heat the residue from the above to 150°, until a constant weight is obtained. The loss represents water of crystallization.

(7) _Carbonates._—Determine the quantity of carbon dioxid evolved by the usual process, and calculate the calcium carbonate.

=286. Solution in Sodium Carbonate.=—Gypsum is also easily decomposed by boiling with a solution of about ten times its weight of sodium carbonate. The calcium, by this operation, is converted into carbonate and can be collected on a gooch, washed, and estimated as usual, but in this case it will contain all the insoluble matters, from which the lime can be separated by solution in hydrochloric acid.

In the filtrate from the above separation the excess of sodium carbonate is removed by the addition of hydrochloric to slight acidity, and the sulfuric acid estimated as described in the preceding paragraph.

Pure gypsum has a composition represented by the following formula: CaSO₄·H₂O.

It contains:

Sulfur dioxid 46.51 per cent.
Lime 32.56 “ “
Water 20.93 “ “

A commercial sample of ordinary gypsum should have about the following composition:[244]

CaSO₄·H₂O 88.15 per cent.
CaCO₃ 3.50 “ “
Fe₂O₃ and Al₂O₃ 1.50 “ “
Insoluble 2.80 “ “
Organic matter 0.50 “ “
Water and undetermined 3.55 “ “

=287. Common Salt.=—Common salt is highly esteemed in many quarters as a top dressing for lawns and meadows, and also for cultivated crops. Its action is chiefly of a mechanical and katalytic nature, since it does not form a very large percentage of the mineral food of plants. On account of its affinity for moisture it is also said to have some value as a condenser and carrier of water in times of drouth. On account of its great cheapness, selling often for less than ten dollars a ton, its use in moderate quantity entails no great expense. Its ability, however, to pay for its own use in the increased harvest is of a doubtful character when it is applied at a cost of more than a few dollars per acre. In the chemical examination of a sample of common salt which is to be used as a fertilizer, a complete analysis is rarely necessary. When desired it can be conducted according to the usual methods of mineral analysis. For practical purposes the moisture, insoluble matter, magnesia and chlorin should be determined and the quantity of sodium chlorid calculated from the latter number. Traces of iodin or bromin which may be present are of no consequence.

The moisture is determined by drying two grams of the well-mixed and finely-powdered sample to constant weight at 100°. The chlorin is obtained by precipitation of an aliquot part of a solution of the salt by set silver nitrate, using potassium chromate as indicator.

In the determination of insoluble matter it should not be forgotten that a little gypsum may be present, and this should be dissolved by rubbing to a finer powder and by repeated digestion in water. The magnesia and lime are separated and determined in the usual manner. If the quantity of gypsum present be sufficient to warrant it the sulfuric acid may be separated and weighed in the manner already described. Common salt when present in the soil in proportions greater than one-tenth per cent is injurious to vegetation.

=288. Green Vitriol.=—When iron is used as a fertilizer it is usually applied as ferrous sulfate. The value of iron in a soil is incontestable and by reason of the fact that fertile soils are always well aerated the iron present in the arable layer is found in the ferric state. When green vitriol is applied to the soil it undergoes gradual oxidation and appears finally in a more highly oxidized form. Iron acts directly on the plant in promoting the development of the chlorophyll cells, and is also found in almost all parts of the vegetable organism. A too great quantity of ferrous sulfate is destructive of plant growth in which respect it resembles common salt. It should therefore be applied with due regard to the dangers which might arise from an excessive quantity. It is not likely, however, that when applied in a finely powdered state at the rate of from two to four hundred pounds per acre it would ever prove poisonous to vegetation.

In the analysis of a sample of green vitriol it will be sufficient to determine the moisture, water of crystallization, iron, and sulfuric acid. The moisture may be ascertained by drying the finely powdered sample over sulfuric acid for a few hours. The water of crystallization is separated by exposing the sample to a temperature of 285° for two hours. The iron may be determined by oxidizing to the ferrous state by boiling with nitric acid and then precipitating with ammonia, and proceeding as directed for iron analysis. The sulfuric acid is separated as barium sulfate and determined as already directed.

=289. Stall Manures.=—There are no definite methods to be described for the analyses of that large class of valuable fertilizer produced in the stable and pen, and which collectively may be called stall manures. The methods of sampling have already been described,[245] but only patience and tact will enable the collector to get a fair representation of the whole mass. These manures are a mixture of urine, excrement, waste fragments of fodder, and the bedding used for the animals. With them may also be included the night soil and waste from human habitations and the garbage from cities. All of these bodies contain valuable plant foods and the phosphoric acid, potash, and nitrogen therein are to be determined by the methods already given for these bodies when they occur in, or are mixed with, organic matter. In general, stall manures are found to have a higher manurial value than is indicated by the amount of phosphorus, potash, and nitrogen which they contain. Through them there is introduced into the soil large quantities of humus bodies whereby the physical state of the soil is profoundly modified and its adaptability to the growth of crops, as a rule increased. The addition of active nitrifying ferments in stall manure is also advantageous. Stall manures, however, may in many cases prove to be injurious to a crop, as for instance, when they are applied in a poorly decomposed state and in a season deficient in moisture.

It is essential therefore that the bedding of animals be in a finely divided state, whereby not only are the absorptive powers of the organic matter increased but also the conditions for their speedy decay favored. To avoid the loss of ammonia arising from decomposing urine it is advisable to compost the stall manure with gypsum or to sprinkle it from time to time with oil of vitriol.

In the analysis the moisture may be estimated by drying a weighed portion of the sample to constant weight at 100° or at a lower temperature in a vacuum. The potash and phosphoric acid are determined as usual, with previous careful incineration, and the nitrogen secured by the moist combustion process.

=290. Hen Manure.=—This fertilizing substance is a mixture of the excrement of the fowl yard with feathers, dust, and other débris. Measured by the standard applied to commercial fertilizers hen manure has a low value. As in the case of other farm manures, however, it produces effects quite out of proportion to the amount of ordinary plant foods which it contains. In a sample examined at the Connecticut station the percentages of fertilizing constituents were found to be the following[246]:

Water 51.84
Organic and volatile matters 24.27
Ash 23.89

The organic matter contained 0.61 per cent of nitrogen as ammonia and the ash 0.97 per cent of phosphoric acid, and 0.59 per cent of potash, all calculated to the original weight of the sample. The percentage of water in this sample is undoubtedly higher than the average, so that it can hardly be taken to represent the true composition of this manure. The potash, phosphoric acid, and nitrogen are to be determined by some one of the standard methods already described, the two former after careful incineration.

=291. Guanos and Cave Deposits.=—The principal constituents of value in these deposits are nitrogen and phosphoric acid. The other organic matters are also of some value but have no commercial rating. The nitrogen may be present in all its forms; _viz._, organic, ammoniacal, amid, and nitric, and for this reason is well suited not only to supply nourishment to the plant in the earlier stages of its growth but also to cater to its later wants. In guano deposits in caves, due usually to the presence of bats, similar forms of fertilizers are found and the soluble constituents due to decay and nitrification are protected from the leaching to which they would be subjected in the open air.

In many localities in the United States these deposits are found, but the humidity of our climate has prevented the immense open deposits of guano that characterize some of the arid islands of the Pacific Ocean.

Many bat guanos examined in this laboratory have also been found to contain potash, in one case 1.78 per cent. It is suggested therefore that the analyst do not omit to examine each sample qualitatively for this substance and to determine its amount when indications point to its presence in weighable proportions. In the many samples of bat guano of American origin which have been analyzed in this laboratory in the last few years some very rich in plant food have been found. In one instance the total percentage of nitrogen present, was 10.11 per cent. In some cases the phosphoric acid is high but rarely in conjunction with a high content of nitrogen. In one instance where the total phosphoric acid reached 14.53 per cent, the content of nitrogen was 4.87 per cent.

In respect of the processes of analysis there are no especial directions to be given. The phosphoric acid, as given below, and the potash are to be determined by the usual methods, the total phosphoric acid and potash after the destruction of the organic matter.

In old cave deposits the processes of decay and nitrification seem to have long been completed and we have found very little power of inducing nitrification in culture solutions seeded from these samples.

=292. French Official Method for Total Phosphoric Acid in Guanos.=—To determine the phosphoric acid in guanos, the method officially adopted by the French agricultural chemists may be used.[247]

Two grams of the sample are rubbed up in a porcelain crucible with a decigram of slaked lime to prevent the possible reduction of the phosphoric acid by the organic matter. The mixture is slightly moistened with a few drops of water, dried on a sand-bath, and afterwards heated to redness, best in a muffle, until organic matter is destroyed. The contents of the crucible are detached and placed in a flask of 200 cubic centimeters capacity. The crucible is well digested twice with some hydrochloric acid to dissolve any adhering fragments, and finally washed with hot water, the acid and water being added to the flask. The contents of the flask are boiled for fifteen minutes and then poured into a flat-bottomed dish, the flask well rinsed three or four times with small quantities of water, and the liquor and washings are evaporated to dryness to render the silica insoluble. The residue is taken up by a mixture of ten cubic centimeters each of hydrochloric acid and water, heated for a few minutes and filtered, and the dish well washed with successive small portions of water, but the total volume of the filtrate and washings should not exceed eighty cubic centimeters. In this filtrate the phosphoric acid may be determined by any one of the approved methods.

=293. Waste Leather.=—This material belongs probably to that class of nitrogenous substances which has already been considered in paragraph =149=. The chief manurial value of the waste is found in its nitrogenous content. The value of this for available plant food has been investigated by Lindsey.[248] A complete resumé of the literature of the subject is also given by him.

The best way of identifying leather waste is by the process proposed by Dabney.[249] It depends on the color produced in a solution of iron phosphate by the tannin compounds derived from the leather. The reagent is prepared by dissolving a freshly made precipitate of iron phosphate from ten grams of ferric chlorid in 400 cubic centimeters of an aqueous solution of forty grams of glacial phosphoric acid. A gentle heat promotes the solution of the phosphate.

In the case of a fertilizer supposed to contain leather, about one gram of the material is treated with thirty cubic centimeters of water and a few drops of sulfuric acid. The mixture is boiled and poured on a filter. To a portion of the filtrate some of the solution of iron phosphate is added, and the mixture made alkaline with ammonia. If leather be present in the sample, a purple or wine color will be developed. Lindsey could easily detect the leather when it was added in ten per cent quantities by the above method, and he regards this method as superior to the microscope which is unreliable in the case of finely ground material.

While leather, as such, decays slowly, and therefore is not at once available for the nourishment of plants it acquires greater utility after digestion in sulfuric acid. Artificial digestion experiments with leather previously treated with sulfuric acid show that, approximately, seventy per cent of the nitrogen pass into solution. Such a prepared leather has, therefore, a digestive coefficient in respect of nitrogen not much inferior to most organic bodies.

In comparative trials with sodium nitrate it was demonstrated that nitrogen in leather, previously dissolved in sulfuric acid, has a rank of about sixty when it is rated at one hundred in the soda salt.

For the estimation of the nitrogen in leather the moist combustion process is to be preferred.

=294. Analysis of Wood Ashes.=—The only kinds of ashes used extensively for manurial purposes are those derived from the burning of hard woods. The ash of soft woods, such as the pine, is too poor in plant foods to warrant its transportation to any great distance for manurial purposes. The methods of incineration of organic bodies for the purpose of obtaining and estimating their mineral contents will be fully discussed in the third volume of this work.

It is important in ash analysis to know whether there be enough of iron present to combine with all the phosphoric acid. For manurial purposes it will be found sufficient to determine the percentages of potash and phosphoric acid alone. For hygienic purposes it is advisable to examine the ash qualitatively and, if necessary, quantitatively for zinc, lead, copper, boric acid, and other bodies of a similar character which may be naturally present in the ash, or may have been added to the organic substance from which it was prepared for preservation or other purposes. The methods of making these special investigations will be discussed in the succeeding volume. At present will be given, however, not only the methods for detecting phosphoric acid and potash, but also for a complete analysis of an ash in so far as its usual constituents are concerned.

=295. Carbon, Sand, and Silica.=—The official agricultural chemists have recommended the following procedure for the determination of the unburned carbon, and the sand and silica.[250]

Five grams of the ash are treated in a beaker, covered with a watch glass with fifty cubic centimeters of hydrochloric acid of 1.115 specific gravity, and digested on the water-bath until all effervescence has ceased. The cover is then removed and the liquid evaporated to complete dryness to render the silica insoluble. The residue is moistened with two or three cubic centimeters of hydrochloric acid and taken up with about fifty cubic centimeters of water, allowed to stand on the water-bath a few minutes, filtered, and thoroughly washed. The filtrate and washings are made up to a quarter of a liter for analysis. The residue is washed from the filter into a platinum dish and boiled about five minutes with twenty cubic centimeters of a saturated solution of pure sodium carbonate; afterwards a few drops of pure sodium hydroxid solution are added and the liquid allowed to settle, and it is then decanted through a tared gooch. The residue is boiled with sodium carbonate solution and decanted as before, a second and a third time, and finally brought upon the felt and thoroughly washed, first with hot water, then with a little dilute hydrochloric acid, and finally with hot water until free of chlorids. The residue in the gooch is dried at 110° to constant weight, giving the carbon and sand. It is then incinerated and the weight of the sand determined, the difference giving the carbon. It is advisable to examine the sand with a microscope to determine if it be pure. The alkaline filtrate and washings from the carbon and sand are acidified with hydrochloric, evaporated to dryness, and the silica separated and determined in the usual way.

Instead of determining soluble silica directly from the sodium carbonate solution, as above, another portion of the ash may be treated with hydrochloric acid and evaporated to dryness as before described, filtered on an ordinary filter, washed, burned, and weighed, giving the weight of silica plus sand, from which the weight of sand is deducted to obtain soluble silica. It is inadmissible to separate the soluble silica from the residue after it has been ignited.

Instead of limiting the quantity of hydrochloric acid used for moistening the dried residue, as suggested above by the official chemists, enough should be employed to fully saturate the mass. The weight of pure ash is obtained by subtracting from the weight of the sample taken the sum of the weights of carbon, sand, and carbon dioxid.

=296. Ferric Phosphate and the Alkaline Earths.=—The ferric phosphate, lime, magnesia, and manganese are determined in an aliquot part of the first hydrochloric acid solution and washings obtained above. Fifty or one hundred cubic centimeters may be used, corresponding to one or two grams of the original ash. The accurately measured quantity of the solution is carefully treated with ammonia until the precipitate formed on its addition becomes permanent on shaking. Ammonium acetate and acetic acid are then added until the mixture has assumed a strongly acid reaction. The separation of the ferric phosphate precipitate is promoted by gentle warming, and it is separated by filtration without unnecessary delay. If the precipitate be not large the sample contains no manganese and alumina in weighable quantities, and if the filtrate be not red the precipitate be washed with hot water containing a little ammonium nitrate. It is then ignited and weighed as Fe₂P₂O₈ and the quantity of ferric oxid computed therefrom. If, however, the precipitate be large it is well washed as above and then dissolved in as small a quantity as possible of hydrochloric acid, and the solution is again precipitated as above by the addition of ammonia, ammonium acetate, and acetic acid. The ferric phosphate obtained by the second precipitation is treated exactly as above described.

In case, however, any weighable quantities of manganese or alumina are present it will not do to weigh the precipitate of ferric phosphate directly even after a second precipitation. Also if the filtrate at first obtained have a red color the precipitate may contain basic ferric phosphate. In this latter case it should be ignited and weighed, then dissolved in hydrochloric acid and the ferric oxid estimated in the solution and from the difference the quantity of combined phosphoric acid calculated.

The separation of the iron from the phosphoric acid may be accomplished by adding tartaric acid to the hydrochloric acid solution of the iron phosphate above obtained and then ammonium chlorid and ammonia. The mixture is placed in a flask and ammonium sulfid added. The flask is closed, placed in a warm place, and allowed to stand until the supernatant liquid is clear and of a pure yellow color without a trace of green. The iron is separated by filtration, washed, dissolved, and estimated in the usual way.

If manganese and alumina be present the iron and manganese are separated from the phosphoric acid and alumina by the processes just given for the separation of iron from phosphoric acid. In the filtrate the alumina and phosphoric acid are separated as follows: The filtrate is evaporated in a platinum dish after the addition of an excess of pure sodium carbonate until no ammonia is set free by a further addition of the carbonate. Some nitric acid is then added and the evaporation continued to dryness. The residue is fused and after cooling softened with water, washed into a small beaker, some hydrochloric acid added, warmed, and filtered. Ammonia is next added until the reaction is alkaline. If no precipitate be produced no alumina is present. In this case more nitric acid is added, the solution again evaporated, and the phosphoric acid determined by the usual methods.

In case a precipitate is formed, showing the presence of alumina, nitric acid is added until the precipitate is dissolved, and then in slight excess and after evaporation the phosphoric acid separated by molybdic solution and determined as usual. From the filtrate the excess of molybdic acid is removed by hydrogen sulfid and the alumina determined in the filtrate: Or the alumina may be determined directly in the hydrochloric acid solution of the melt above obtained as aluminum phosphate by adding sodium phosphate, ammonia and acetic acid. The aluminum phosphate is separated by filtration and determined in the usual manner. The phosphoric acid is then determined in another aliquot part of the original filtrate from the first solution of the ash.

Since most ashes contain an excess of phosphoric acid above the quantity required to combine with the iron it is preferable to proceed on that basis as described in the next paragraph.

=297. Method Used in this Laboratory.=—The principle of the method rests on the assumption that all the phosphoric acid may be removed from the solution by the careful addition of iron chlorid. Any excess of iron is then removed by ammonium acetate and the manganese, lime, and magnesia, are separated in the filtrate. The percentage of iron is determined by reduction of the iron in another portion of the solution and titration with potassium permanganate. The process as conducted by McElroy, is as follows:[251]

_Moisture._—If the ash contain much carbon the water is best determined by drying in vacuo to avoid oxidation.

_Sand, Silica, and Carbon._—Place a portion of the ash in a weighed platinum dish, weigh, and cover the sample with hydrochloric acid of 1.115 specific gravity. Evaporate to dryness on the water-bath, and then heat for fifteen minutes at 105° to 110° in an air-bath. Repeat the treatment with acid and drying: Finally cover with a third portion of acid and digest on the water-bath for an hour or two. Filter into a weighed gooch and wash the residue free of chlorids. The gooch is best weighed with the dish to avoid the necessity of transferring the silica which may adhere to the sides of the former. Dry at a few degrees above the boiling temperature of water and weigh. Where the ash contains much charcoal the drying is best done in a vacuum at 60° to 70°. The increase in weight found represents sand, silica, and carbon: Burn and reweigh. The loss is carbon.

Another portion of ash is treated as before except that it is filtered through a paper filter. The filtrate is united with that of the previous sample in a graduated flask. When the washing is completed the filter is placed in the dish, a weak solution of caustic soda added, and the mixture heated on the water-bath for some time. Decant while hot through a fresh filter and retreat the residue in the dish with another portion of alkali. Finally wash with hot water till the alkaline reaction disappears, then with weak hydrochloric acid, then with water until chlorids disappear. The washed mass on the filter is transferred to a platinum dish and ignited. The weight obtained represents sand.