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3. Boil the ochreous or sinter-deposit for a considerable time with concentrated solution of potassa or soda, and filter. a. Acidify a portion of the filtrate with acetic acid, add ammonia, let the mixture stand 12 hours, and then filter the fluid from the precipitate of alumina and hydrated silicic acid, which usually forms; again add acetic acid to acid reaction, and then a solution of neutral acetate of copper. If a brownish precipitate is formed, this consists of APOCRENATE of copper. Mix the fluid filtered from the precipitate with carbonate of ammonia, until the green color has changed to blue, and warm. If a bluish-green precipitate is produced, this consists of CRENATE of copper.

b. If you have detected arsenic, use the remainder of the alkaline fluid to ascertain whether the arsenic existed in the sinter as arsenious acid or as arsenic acid. Compare § 137, 9.

IV. ANALYSIS OF SOILS.
§ 218.

Soils must necessarily contain all the constituents which are found in the plants growing upon them, with the exception of those supplied by the atmosphere and the rain. When we find, therefore, a plant the constituent elements of which are known, growing in a certain soil, the mere fact of its growing there gives us some insight into the composition of that soil, and may accordingly save us, to some extent, the trouble of a qualitative analysis.

Viewed in this light, it would appear quite superfluous to make a qualitative analysis of soils still capable of producing plants; for it is well known that the ashes of plants contain almost invariably the same constituents, and the differences. between them are caused principally by differences in the relative proportions in which the several constituents are present. But if, in the qualitative analysis of a soil, regard is had also-in so far as may be done by a simple estimationto the quantities and proportions of the several constituent ingredients, and to the state and condition in which they are found to be present in the soil, an analysis of the kind, if combined with an examination of the physical properties of the soil, and a mechanical separation of its component parts,*

* With regard to the mechanical separation of the component parts of a soil, nd the examination of its physical properties and chemical condition, compare Fr. Schulze's paper, "Anleitung zur Untersuchung der Ackererden auf ihre wichtigscen physikalischen Eigenschaften und Bestandtheile."-Journal f. prakt. Chemie, Vol 47, p. 241.

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may give most useful results, enabling the analyst to judge sufficiently of the condition of the soil, to supersede the necessity of a quantitative analysis, which would require much time, and is a far more difficult task.

As plants can only absorb substances in a state of solution, it is a matter of especial importance, in the qualitative analysis of a soil, to know which are the constituents that are soluble in water;* which those that require an acid for their solution (in nature principally carbonic acid); and, finally, which those that are neither soluble in water nor in acids, and are not, accordingly, in a position for the time being to afford nutriment to the plant. With regard to the insoluble substances, another interesting question to answer is, whether they suffer disintegration readily, or slowly and with difficulty, or whether they altogether resist the action of disintegrating agencies; and also what are the products which they yield upon their disintegration.t

In the analysis of soils, the constituents soluble in water, those soluble in acids, and the insoluble constituents must be examined separately. The examination of the organic portion also demands a separate process.

The analysis is therefore properly divided into the following four parts:

1. Preparation and Examination of the Aqueous Extract.

§ 219.

About two pounds (1000 grammes) of the air-dried soil are 269 used for the preparation of the aqueous extract. To prepare this extract quite clear is a matter of some difficulty; in following the usual course, viz., digesting or boiling the earth with water, and then filtering, the fine particles of clay are speedily found to impede the operation, by choking up the pores of the filter; they also almost invariably render the

* Since the discovery that the soil, like porous charcoal, possesses the power of removing dissolved matters from solutions, the formerly received notion that those matters which are soluble in water, or in water containing carbonic acid, are free to move in the soil has been necessarily modified. We must conclude that the water extract of a soil does not accurately represent what is present in the soil in a form accessible to plants. Certainly it cannot contain these substances in the proportion in which they exist in the soil, because the absorptive power of the soil is exerted more forcibly towards some substances than towards others. Although for these reasons the analysis of the aqueous solution of a soil can no longer be valued as formerly, yet it is often of interest to know what substances really are dissolved by water from an earth, and I have therefore retained this chapter.

For more ample information on this subject I refer the reader to Fresenius' "Chemie für Landwirthe, Forstmänner und Cameralisten;" published at Brunswick by F. Vieweg & Son, 1847, p. 485.

filtrate turbid, at least the portion which passes through first. I have found the following method the most practical.* Close the neck of several middle-sized funnels with small filters of coarse blotting paper, moisten the paper, press it close to the sides of the funnels, and then introduce the air-dried soil, in small lumps ranging from the size of a pea to that of a walnut, but not pulverized or even crushed; fill the funnels with the soil to the extent of about two-thirds. Pour distilled water into them, in sufficient quantity to cover the soil; if the first portion of the filtrate is turbid, pour it back on the filter. Let the operation proceed quietly. When the first quantity of the fluid has passed, pour on more and continue the lixiviation until the weight of the filtrate is two or three times as great as that of the soil employed. Unite the several filtrates and set aside a portion of the washed earth for further examination.

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a. Concentrate two-thirds of the aqueous solution by 270 cautiously evaporating in a porcelain dish, filter off a portion, and test its reaction; put aside a portion of the filtrate for the subsequent examination for organic matters, according to the directions of (280). Warm the remainder, and add nitric acid. Evolution of gas indicates the presence of an ALKALINE CARBONATE. Then test with nitrate of silver for CHLORINE. b. Transfer the remainder of the concentrated fluid, together with the precipitate which usually forms in the process of concentration, to a small porcelain, or, which is preferable, a small platinum dish, evaporate to dryness, and cautiously heat the brownish residue over the lamp until complete destruction of the organic matter is effected. In presence of NITRATES this operation is attended with deflagration, which is more or less violent according to the greater or smaller proportion in which these salts are present. c. Test a small portion of the gently ignited residue with carbonate of soda before the blowpipe for MANGANESE. d. Warm the remainder with water, add some hydrochloric acid (effervescence indicates the presence of CARBONIC ACID), evaporate to dryness, heat a little more strongly, to effect the complete separation of the silicic acid, moisten with hydrochloric acid, add water, warm, and filter. The washed residue generally contains some carbon, and also a little clay-if the aque

* Recommended by Fr. Schulze “ Anleitung zur Untersuchung der Ackererden auf ihre wichtigsten physikalischen Eigenschaften und Bestandtheile."-Journ. f. prakt. Chemie, vol. 47, p. 241.

ous extract was not perfectly clear-and lastly SILICIC
ACID. To detect the latter, make a hole in the point of
the filter, rinse the residue through, boil with solution of
carbonate of soda, filter, saturate with hydrochloric acid,
evaporate to dryness, and treat the residue with water,
which will leave the silicic acid undissolved.

e. Test a small portion of the hydrochloric acid solu- 271
tion with chloride of barium for SULPHURIC ACID; another
portion with nitric solution of molybdate of ammonia for
PHOSPHORIC ACID; a third portion with sulphocyanide of
potassium for SESQUIOXIDE OF IRON. Add to the remain-
der a few drops of sesquichloride of iron (to remove the
phosphoric acid), then ammonia cautiously until the fluid
is slightly alkaline, warm a little, filter, throw down the
LIME from the filtrate by means of oxalate of ammonia,
and proceed for the detection of MAGNESIA, POTassa, and
SODA, in the usual way, strictly according to the direc-
tions of § 199.

f. Alumina is not likely to be found in the aqueous 272 extract. (Fr. Schulze never found any.) However, if you wish to test for it, boil the ammonia precipitate obtained in (271) with pure solution of soda or potassa, filter, and test the filtrate with chloride of ammonium.

g. If you have detected iron, test a portion of the 273 remaining third of the aqueous extract with ferricyanide of potassium, another with sulphocyanide of potassium, both after previous addition of some hydrochloric acid: this will indicate the degree of oxidation in which the iron is present. Mix the remainder of the aqueous extract with a little sulphuric acid, evaporate on the water-bath nearly to dryness, and test the residue for AMMONIA, by adding hydrate of lime.

2. Preparation and Examination of the Acid Extract.

§ 220.

1. Heat about 50 grammes of the soil from which the part 274 soluble in water has been removed as far as practicable,* with moderately strong hydrochloric acid (effervescence indicates CARBONIC ACID) for several hours on the water-bath, filter, and make the following experiments with the filtrate, which, owing to the presence of sesquichloride of iron, has in most cases a yellow color:

Test a small portion of it with sulphocyanide of potassium 275

* Complete lixiviation is generally impracticable.

for SESQUIOXIDE OF IRON, another with ferrocyanide of potassium for PROTOXIDE OF IRON.

2. Test a small portion with chloride of barium for SULPHURIC ACID, another with molybdate of ammonia for PHOSPHORIC

ACID.

3. Mix a larger portion of the filtrate with ammonia to 276 neutralize the free acid, then with yellowish sulphide of ammonium; and let the mixture stand in a warm place until the fluid looks yellow; then filter, and test the filtrate in the usual way for LIME, MAGNESIA, POTASSA, AND soda.

4. Dissolve the precipitate obtained in 3, in hydrochloric 277 acid, evaporate the solution to dryness, moisten the residue with hydrochloric acid, add water, warm, filter, and examine the filtrate according to the directions of (150), for IRON, MANGANESE, ALUMINA, and, if necessary, also for lime and magnesia, which may have been thrown down by the sulphide of ammonium, in combination with phosphoric acid.

5. The separated SILICIC ACID obtained in 4 is usually colored by organic matter. It must, therefore, be ignited to obtain it pure.

6. If it is a matter of interest to ascertain whether the 278 hydrochloric acid extract contains ARSENIC ACID, OXIDE OF COPPER, &c., treat the remainder of the solution first with hyposulphite of soda, then with hydrosulphuric acid, as directed in (262) to (264).

7. Should you wish to look for FLUORINE, ignite a fresh portion of the earth, and then proceed according to the directions of (230).

3. Examination of the Inorganic Constituents insoluble in Water and Acids. § 221.

The operation of heating the lixiviated soil with hydro- 279 chloric acid (274) leaves still the greater portion of it undissolved. If you wish to subject this undissolved residue to a chemical examination, wash, dry, and sift, to separate the large and small stones from the clay and sand; moreover, separate the two latter from each other by elutriation. Subject the several portions to the analytical process given for the silicates (§ 208).

4. Examination of the Organic Constituents of the Soil.* § 222.

The organic constituents of the soil, which exercise so great an influence upon its fertility, both by their physical

* Compare Fresenius' "Chemie für Landwirthe, Forstmänner und Cameralisten;" published at Brunswick, by F. Viewey and Son, 1847, § 282-285.

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