(1) The Metaphenylenediamine Test.-The solution is made by dissolving 5 grms. of metaphenylenediamine in 100 c.c. of water and slightly acidifying with sulphuric acid. A c.c. of the reagent added to 50 c.c. of the water strikes a pale yellow to a deep orange red, according to the quantity of nitrite present.

(2) Meldola's Test is a solution of para-amido-benzene-azodimethy-aniline in water acidified with hydrochloric acid (strength about 02 per cent.). The reagent is added to the water to be tested, the whole acidified with sulphuric acid, warmed for 15 minutes on the water bath, and then alkalized with ammonia. If nitrites are present, the liquid becomes salmon-coloured when acid; and when alkalized with ammonia, green, with small quantities, and blue with large quantities of nitrite.

(3) The Napthylamine Test.-The water is first treated with sulphuric acid, acidified, and a solution of hydrochloride or sulphate of napthylamine added. A minute trace of nitrite strikes a pale pink; if much nitrite be present there is a ruby colour produced, and the solution becomes turbid from the separation of colouring matter.

The above three tests are of great delicacy, detecting one part of nitrite dissolved in several millions of water.

Detection of Nitrates.-There is no qualitative test for nitrates not shared with nitrites; in the absence of nitrites, the diphenylamine test is very convenient. Diphenylamine is dissolved in a little water by the aid of strong sulphuric acid. A few drops of the solution are added to 10 or 20 c.c. of water and double the volume of sulphuric acid. A purple blue colour denotes presence of nitrates.

Reaction of Water.-Nearly all waters are alkaline, and strike therefore a yellow colour with methyl orange, a dark red with cochineal. If acid, the colour with methyl orange is reddish orange, with cochineal a yellow tint.

DETECTION OF METALS.

Iron.-A mixture of ferro and ferridcyanide of potash strikes a blue colour.

Lead or Copper.—A solution of cochineal strikes in a neutral or alkaline solution a feeble red having a faint blue tinge to a deep mauve blue, according to the quantity present. Hydric sulphide

gives a brown to black colour. Lead is distinguished from copper by the ferrocyanide test. A solution of potassic ferrocyanide added to a water containing a trace of copper, gives a brown colour, or if more than a trace be present, there will be a precipitate. Zinc.-Potassic ferrocyanide added to a filtered and acidulated water containing zinc, gives a light white cloud or heavy precipitate according to the amount present.

(111) Quantitative Chemical Examination.

Merely qualitative examination of water is in the majority of instances insufficient, and it is necessary to know the amounts of certain constituents in water. Here will be described the simplest processes only, and it will be presumed that the reader is unacquainted with practical details. The first thing is to fit up some small room as a laboratory. To work with comfort it will be necessary to have a good sink in the room to carry away refuse liquids, and to have water and gas laid on. There should be a water-tap over the sink and water and gas laid on with taps with straight nozzles at 3 feet intervals along the working bench. The bench or table should be not more than 20 inches high, for all the apparatus is elevated by means of stands and a high bench is not so convenient for working.

The chemical apparatus required to determine chlorine, nitrogen as nitrates, free ammonia, albuminoid ammonia, oxygen consumed, sulphates, hardness, total solid residue, is as follows (the prices given are from Townsen and Mercer's list): - A balance to carry 100 grms. in each pan and to turn when loaded with half a milligrm. (£6 15s.); a box of grm, weights (£1 15s.); 1 platinum dish to contain 100 c.c. of water, (about £2 78.); a copper water bath, with holes cut in it for the reception of the dishes; a set of glass and porcelain dishes; a porcelain slab; graduated flasks, either 100 c.c., 500 c.c., and 1 litre, or if preferred, 70 c.c. and 700 c.c. These flasks have a circular mark scratched on the neck, and contain the exact quantity when they are filled up to this mark. Two or three retorts, each capacious enough to hold a litre; the retorts should be tubulated and stoppered; a copper air bath, with a Page's regulator and thermometer; at least two burettes, with stand; a Liebig's condenser, with adapter and stand; Nesslerising cylinders;

retort holder, with universal joint clip; triangular stands; asbestos mill-board; wire gauze; triangles made of wire, covered with pieces of tobacco pipe for the support of platinum or porcelain dishes during ignition; one or two pairs of crucible tongs; filter paper; corks; cork-borers; distilled water; pure sulphuric acid; pure hydrochloric acid; pure potash; potassic permanganate; silver nitrate; potassic iodide; potassic chromate; sulphate of copper; zinc foil; ammonic chloride; calcic carbonate; mercuric chloride; pure sodic chloride; sodic hyposulphite; methyl orange.

(112) Solutions Required for the Analysis.

With these reagents and apparatus, the first thing to be done is to make up the following solutions which are arranged here in alphabetical order for facility of reference :

Ammonium Chloride 3146 grm., pure distilled water 1 litre, each cc. contains 0001 grm. of ammonia, that is one-tenth of a milligramme.

Calcic Chloride Solution.-Pure calcic carbonate, 2 grm.; dissolve in just sufficient dilute hydrochloric acid, evaporate to dryness in a platinum dish, and dissolve in a litre of water.

Copper Sulphate.-Copper sulphate, 30 grms. made up to a litre with distilled water.

Nessler Solution.-35 grms. of potassic iodide are dissolved in 100 c.c. of water, 17 grms. of pure mercuric chloride are boiled in 300 c.c. of water and then cooled. The mercuric solution is added little by little to the potassium iodide, until a permanent precipitate is formed. The liquid is now made up to a litre, with a solution of sodic hydrate (strength, 20 per cent.). Lastly, the reagent is made more sensitive by the final addition of a little more of the mercuric chloride solution, until a permanent precipitate begins to form. The solution is put on one side to deposit, and the clear liquid decanted for use.

Potassium Iodide Solution.-Potassium iodide, 1 part, dissolved in 10 parts of water.

Potassium Monochromate.-Potassium monochromate 50 grms. dissolved in a litre of water.

Potassium Permanganate.—(a) Alkaline; potassic permanganate 8 grms., potassium hydrate 200 grms., distilled water 1,100 c.c., the solution is boiled down to 1,000 parts, and kept in properly stoppered

bottles. (b) Standard volumetric for oxygen process; 395 grms. of potassic permanganate is dissolved in a litre of water. Each c.c. contains 0001 grm, of available oxygen.

Silver Nitrate, Standard Solution of.-4.7887 grms. of silver nitrate are dissolved in pure distilled water, and the solution made up so as to measure exactly 1 litre.

Soap, Standard Solution of-150 parts of lead plaster are triturated in a mortar with 40 gims. of dry potassic carbonate, and made into a cream with the addition of absolute alcohol; when dissolved, filter, and by the addition of water reduce the strength to that of proof spirit. The solution of lead soap is then diluted. up with proof spirit to the proper strength. The proper strength is when 14-25 c.c. are required to form a permanent lather with 50 c.c. of the calcic chloride solution.

Sodic Hyposulphite.-One part of crystallized sodic hyposulphite is dissolved in water and the solution made up to 1 litre.

(113) The Operation of Weighing.

One of the first things to be learnt is the operation of weighing on a delicate chemical balance. It is ascertained that the beam swings accurately by allowing the beam to swing without any load in the scales; if the beam swings to one side more than the other the student will find at the top of the beam in the centre, some simple mechanism by turning which the beam is adjusted.

To Read the Weights.-The brass weights from 100 grms. to 1 grm. create no difficulty for they have the figures marked upon them. It may be found convenient to arrange the other weights on a slip of paper in front of the balance with their values marked clearly on the paper thus

52 1 1 05 02 01 01 005 001

the weights are then simply read from the blank spaces, for instance supposing the weights marked with a star are on the balance pan, the small weights taken are obviously 556 grm. for they add up as follows::

.5

⚫05

*005

·001

*556

The weights between 1 milligrm. (001) and 5 milligrms. (005) are most conveniently ascertained by working the rider; each main division equalling a milligrm.

The weights must be taken off in strict order and placed upon the scale by the aid of a pair of forceps. For instance, suppose the weight of a platinum dish should be 38.923 grms. this weight would be ascertained as follows: (1) 50 grms. weight, too heavy; (2) 20 grms. weight, not enough; (3) 10 grms. weight added to the 20, still not enough; (4) 5 grms. weight added to the weights in the pan, not enough; (6) 2 grms. weight added, not enough; (7) 1 grm. weight added, not enough; (8) 1 grm. weight, too heavy; (9) 1 grm. weight removed; (10) 5 grm. added, not enough; (11) ·2 grm. added, not enough; (12) 1 grm. added, not enough; (13) 1 grm., not enough; (14) 05, too heavy; (15) 05 removed and 02 grm, substituted, not enough; (16) 01 grm. added, too heavy, and therefore removed (17) 005 grm. added, too heavy; (20) .005 removed and the balance closed, and the rider worked about the beam between the first and fifth division until the exact balance and swing is found with the rider on the third division.

THE ANALYSIS.

(114) Relation between the Litre and the Gallon.

The analyst can either operate on litres or decimal parts of a litre, or take advantage of the relation that the English grain and the gallon has to cubic centimetres. This relation is such that a milligrm. of residue from 70 c.c. is equivalent to a grain per gallon. For instance, if 70 c.c. of water on evaporation leaves 076 grm., or, in other words, 76 milligrms., the water has a solid residue of 76 grains per gallon, or if a water contain in 70 c.c. *005 of chlorine, that is 5 grains per gallon. If the analyst wishes to return the analysis in parts per 1,000 or per 10,000, it is then best to take 100 c.c. for the solid residue and half a litre or a litre for distillation. Parts per litre, that is parts per 1,000 are easily turned into grains per gallon by multiplying by 70; thus if a litre of water give 0714, that is 4.99 grains per gallon for 0714 × 70 4.99.

=

It will be presumed in the following that the analysis is to be expressed in parts per 1,000.