effected with absolute accuracy when the analyst has access to the source of the

water.

It is then necessary to provide himself, beforehand, with the following apparatus, &c.

A glass vessel, of suitable form, capable of containing about 12 ounces; its capacity must be accurately known. The best form for this vessel is that of an adapter (of course open at both ends), and so narrow at the top as to admit of its being closed with the thumb, so that it may be dipped into the spring, a certain quantity of water withdrawn in it, by closing it with the thumb, and the water allowed to run into the bottles by merely removing the thumb from the orifice. This instrument is sold under the rather inappropriate name of a siphon for mineral

waters.

Four or five stoppered bottles, capable of holding about 16 ounces.

A few ounces of a clear solution of chloride of calcium.

A small quantity of ammonia which does not give any precipitate with chlo ride of calcium.

When at the spring, the operator must introduce about an ounce of solution of chloride of calcium, and an ounce of ammonia, into each of the bottles. A siphon-full of water is then placed in each of the bottles, which are then closely stopped and removed to the laboratory. The precipitates are collected upon a weighed filter, dried at 212° F. and weighed. The dry precipitate is well mixed, to insure its uniformity, and the carbonic acid in a weighed portion of it determined (p. 596). Two or three determinations may be made, to control each other.

The amount of carbonic acid is then calculated for the whole precipitate, and subsequently for an imperial gallon of water.

By deducting, from the total quantity of carbonic acid, that combined with the lime, magnesia, and oxide of iron (previously determined), we ascertain the amount of free carbonic acid present (unless there be any alkaline carbonates).

The degree of hardness of a mineral water is determined by Clark's soup-test, which consists in ascertaining the quantity of a standard solution of soap in spirit, required to produce a permanent lather with a given quantity of the water under examination, the result being expressed in degrees of hardness, each of which corresponds to one grain of carbonate of lime in a gallon (= 70,000 grs. of distilled water) of water.

The soap-solution is prepared by dissolving curd soap (Hawes's white-curd) in proof spirit, in the proportion of about 120 grs. to a piut. In order to graduate this solution, 16 grs. of pure carbonate of lime (calcareous spar, white marble) are dissolved, without loss, in a small quantity of hydrochloric acid; the solution is very carefully evaporated to dryness in an air-bath, the residue redissolved in water, the solution again evaporated, and these operations repeated until a perfectly neutral solution has been obtained.

The neutral solution of chloride of calcium thus prepared is to be diluted with so much distilled water as will make up a gallon; it will then represent a water of 16° hardness. 100 measures of this solution are introduced into a stoppered bottle capable of containing 2,000 grains, and the soap-solution is very gradually added to it from a burette (the stopper being replaced, and the solution violently agitated from time to time), until a lather is formed which remains for five minutes over the whole surface of the liquid, when the bottle is laid down upon the table. The number of measures of soap-solution used is then noticed, and the strength of the solution altered, if necessary, by a further addition either of soap or spirit, until exactly 32 measures of the liquid are required for 100 measures of the water of 16° hardness. The trial should then be repeated, in

Each measure is equal to 10 grs. of distilled water.

2 This standard soap-solution may be purchased at the operative chemist's.

exactly the same way, with the water of 16° hardness, in order to leave no doubt of the strength of the soap-solution.

To apply this test, the water to be examined is introduced into a stoppered bottle, which should be half filled with it, and violently agitated, in order to disengage any free carbonic acid, which would increase the quantity of soap required to form a lather; the air in the bottle is then sucked out through a glass tube, and these operations repeated two or three times, until it is judged that the free carbonic acid is entirely removed. 100 measures of this water are then introduced into a stoppered bottle of twice that capacity, and treated as in the case of the artificial water of 16° hardness (see above), except that the carbonic acid should be sucked out at intervals from the upper part of the bottle. The hardness of the water is then inferred directly from the number of measures of soap-solution employed, by reference to the subjoined table.

If the water is so hard that 32 measures of the soap-solution do not yield a permanent lather, 100 measures of distilled water are added, and the experiment proceeded with in the usual manner, until 60 measures of soap-solution have been used. Should these fail to produce a lather, 100 measures of distilled water are again added, and the operation conducted until 90 measures of soap-solution have been taken; if more soap is even then necessary, its addition must be preceded by that of 100 measures more distilled water. When a lather has been obtained, another experiment is commenced with a mixture of 100 measures of the original water, with the total quantity of distilled water added in the preceding determination. The number of measures of soap solution used, must be divided by the number of 100 measures contained in the mixture, and the degree of hardness corresponding to the quotient having been found by reference to the table, it must be multiplied by the former divisor, to obtain the true degree of hardness. Thus, if the original water had been diluted with 200 measures of distilled water, and had then required 96 measures of soap solution, it would be necessary to divide 96 by 3, and to refer the quotient 32, to the table, where it would be seen to correspond to 16°, which, multiplied by 3, gives 48° for the actual hardness of the water.

If very accurate results be desired, it is recommended to shake the water, to which a sufficiency of soap-solution has been added, at intervals of half an hour, and, should the lather not then continue for five minutes, to add as much more soap-solution as is necessary to produce that effect, even after standing for such a period.

When the number of measures of the soap-solution fall between any two numbers given in the table, the hardness will be expressed, of course, by an integer and a fraction; the integer will be the degree of hardness corresponding to the next lower number in the soap-test column; the numerator of the fraction will be found by subtracting this last number from the actual number of measures employed; and the denominator will be the difference, in the third column, corresponding to the number above referred to in the second column; thus, if 25.8 measures of the soap-solution have been employed, the number 12, opposite to the next lower number, 24.9, in the soap-test column, represents the integral part of the hardness; the numerator of the fractional part is 25.8-24.9 =0.9, and the denominator is 1.8, the difference corresponding to 24.9; the fraction, then, is 0.5, and 12.5 is the hardness required.

According to Clark, the hardness of a water may be inferred from an ordinary analysis, by calculating the total amount, in grains, of carbonate of lime, equivalent to the lime, magnesia, oxides of lime, and alumina, in a gallon of water; the number thus obtained will represent the hardness, in degrees.1

To determine the amount of alkaline carbonate present in a water, the following method is adopted: About 5000 grains of water are boiled for a considerable time, the precipitate filtered off, and well washed. The filtrate is divided into two parts, both of which are accurately weighed. In the one portion, the chlorine is determined as usual. The other is acidified with hydrochloric acid, evaporated to dryness, gently ignited, and the chlorine determined in the aqueous solution of the residue.

The difference between this quantity of chlorine and the former (calculated upon the same quantity of liquid) expresses the amount of chlorine corresponding, equivalent for equivalent, to the alkali present in the form of carbonate.

The sulphuretted hydrogen contained in a water should, if possible, be determined at the spring.

Three or four stoppered bottles are taken, and into each of them a small quantity of a solution of arsenious acid in bydrochloric acid is poured. A siphon-full of water is then introduced into each bottle (as in the determination of carbonic acid). In order to ascertain the amount of the sulphuretted hydrogen, the precipitated tersulphide of arsenic is collected upon a filter of known weight, well washed, dried at 212° F., and weighed.

The amount of sulphuretted hydrogen is then calculated for an imperial gallon.

It is usual to arrange the results of the analysis of a water according to the following general rules (Fresenius); the equivalent numbers are, of course, the data for the calculations:

1. The lime, magnesia, and protoxide of iron, in the precipitate by boiling, are calculated and stated as carbonates, the carbonic acid which they require being calculated, and deducted from the total amount of carbonic acid present.

The remainder is stated as free carbonic acid (unless alkaline carbonates are present).

2. The rest of the lime is calculated and stated as sulphate. The sulphuric acid which it requires is calculated and deducted from the total amount of sulphuric acid; the remainder, if any, is calculated as sulphate of potassa, and should any still remain, it is calculated as sulphate of soda.

3. The rest of the sodium is calculated as chloride.

1 Campbell has made some experiments on the action of the soap-test upon waters containing magnesia, from which he has deduced the following conclusions: 1. That the magnesia, in its behavior to the soap-test, is equivalent to lime, only when its amount does not correspond to more than six graius of lime in a gallon of water 2. That, for many waters, Clark's rule for calculating the hardness from an ordinary analysis, is not

accurate.

4. The remainder of the chlorine is calculated as chloride of magnesium; should any magnesium remain, it must exist as sulphate.

It is obvious that this method of calculation will afford a valuable control for the analysis.

Moreover, the sum of the various inorganic constituents (the iron being calculated as sesquioxide) should be nearly equal to that of the total amount of inorganic matter determined by evaporation.

The amount of alkali existing in the water as carbonate has been determined previously.

ANALYSIS OF SOILS.

§ 442. The following substances are generally found in soils:

Traces of copper, arsenic, &c. have occasionally been detected.

The specimens of soil should be taken at different depths, and from different parts of the field; they should be uniformly mixed, all large stones, roots, &c., picked out, and the soil spread upon a sheet of paper and allowed to dry spontaneously in the air for a day or two; it is then powdered in a mortar, and rubbed, with the fingers, through a piece of muslin stretched over the mouth of a beaker. Preliminary Examination of the Soil.-1. A portion of the soil is heated on platinum to ascertain whether much organic matter is present, which may be known by the carbonization, and whether there is any nitrogenized organic matter, known by the odor of burnt hair which it emits when heated.

2. Another portion is mixed with hydrate of lime, in a dish, the mixture moistened with water, and very gently heated, to test for ammonia.

If the soil be found to contain a large quantity of organic matter, it should be very gently ignited previously to examination, and, in this case, nitric and carbonic acids must be sought in the unignited soil; after ignition we must expect to find some of the sulphate of lime reduced to sulphide of calcium, and the sesquioxide of iron reduced to oxide.

It must be remembered that our object in analyzing a soil is not merely to ascertain what substances are present, but also to determine the condition in which they are contained in the soil, whether they are soluble or insoluble; whether, for example, the lime is present as sulphate or as carbonate; whether the alkalies are soluble and ready to be absorbed by the plant, or whether they exist in the form of insoluble silicates, which are, at present, useless.

The examination of the soil must therefore be divided into three parts :— 1. Analysis of the portion soluble in water.

2. Analysis of the portion soluble in hydrochloric acid.

3. Analysis of the insoluble residue.

QUALITATIVE ANALYSIS.

Examination of the portion soluble in Water.-About eight ounces of the soil are boiled, in a dish, with a pint of water, for half an hour, and filtered. The filtrate is evaporated to about one ounce, and divided into two parts. One portion is examined as usual for bases.

The other portion is tested in the ordinary manner, for sulphuric, phosphoric, hydrochloric, and nitric acids.

Examination of the portion soluble in Hydrochloric Acid. About of the residue left by water is introduced into a flask, and boiled, for about ten minutes, with concentrated hydrochloric acid; water is then added, the boiling continued for some time, and the solution filtered. (If the residue effervesced when treated with hydrochloric acid, it indicates the presence of carbonic acid.)

A small portion of the hydrochloric solution is tested with chloride of barium, for sulphuric acid.

Another small portion is set aside.

The greater part of the hydrochloric solution is examined for bases and for phosphoric acid according to the general process.

Examination of the insoluble Residue. This residue is dried and divided into two parts.

One part is analyzed according to Table VIII.

The other portion is examined for alkalies according to Table VIII.

A portion of the original soil may be tested for hydrofluoric acid by the terfluoride of silicon test (p. 536).

A portion of the original soil should be ignited and tested for manganese, by fusion with carbonate of soda and nitre.

QUANTITATIVE ANALYSIS.

The method here given for the quantitative analysis of soils, will include the determination of the following substances: potassa, soda, lime, magnesia, alumina, oxide of manganese, oxide and sesquioxide of iron, sulphuric, phosphoric, silicic, carbonic, and hydrochloric acids, organic matter, and water.

Determination of Water.-About 250-300 grains of the air-dried soil, are heated in a water-bath till the weight is constant. The loss represents the amount of water.

Determination of Organic Matter.-About 50 grains of the perfectly dried soil are introduced into a platinum crucible, accurately weighed, and completely incinerated with the usual precautions (p. 573). The residue is allowed to cool, moistened with sesquicarbonate of ammonia (to recarbonate any caustic lime), and dried in an air-bath, at a little above 212° F. till its weight is constant.

The loss indicates the total quantity of organic matter in the dry soil, which is then calculated for 100 parts of air-dried soil.

Determination of the total amount of Carbonic Acid.-About 50 grains of the air-dried soil are employed for the determination of carbonic acid by the method of Fresenius and Will (see p. 596).

Determination of the total amount of Constituents soluble in Water.-From500 to 600 grains of air-dried soil are heated with four or five ounces of water, in a beaker, for a considerable period, nearly to ebullition; the residue is allowed to subside perfectly, the solution poured through the filter, and the residue again heated with water; this operation is repeated, till a few drops of the solution do not leave any considerable residue when evaporated on platinum.

The residue is thrown upon a weighed filter, washed with hot water till the washings leave no appreciable residue when evaporated, dried in a water-bath, and weighed.