closed by a cork; through this two bent tubes are passed, the one, a, for the admission of air into the bottle, and the other, b, which reaches nearly to the bottom, for the escape of the water.

Fig. 40.

The external orifice of the latter is drawn to a fine point, which should never exceed onefortieth of an inch in diameter. The opening of the tube can be widened by grinding it upon a sandstone, or rubbing it with a file which has been moistened with camphorized turpentine; or it may be narrowed by holding it in the flame of the spirit-lamp, or before the Blowpipe. The bottle, when corked, should be a little more than half full.

When wanted for use, the operator blows into the tube, a, and

the pressure to which the water is subjected, forces it through the tube in a fine stream, which can be directed upon the precipitate in the filter.

Near the end of the edulcoration, the jet of water should be directed towards the edges of the filter, and not upon the precipitate itself, by which means any particles of the latter adhering to the paper, are washed to the bottom, and brought into a small compass.

Gelatinous precipitates require much washing; the jet of water may occasionally be deficient in force, and not strong enough to detach them. In this case they may be stirred up with a glass rod, but the operator must be careful not to force the rod through the paper, otherwise the filtration will have to be repeated. It is to be observed, that after every addition of water, no more is to be added until the first quantity has filtered through, otherwise an affusion of the precipitate is not effected, but only a continued dilution of the solution.

27. WATCH-GLASSES, two inches in diameter, Fig. 41, a.

D

These may be employed either as testglasses, or as crucible-covers during the refining process.

28. GLAZED PORCELAIN BASINS, of various sizes, are very useful for the precipitation or evaporation of liquids and also for heating, in the dry state, earths and metallic oxides with reagents, The form of two such vessels is given. in Figs. 41 and 42.

29. A cylindrical BOTTLE, of lacquered sheet iron, provided with a screw top, for containing lamp oil.

VI. REAGENTS.

Fig. 41.

a

Fig. 42.

Those substances which operate upon others in any remarkable manner so as to lead to their detection, whether by change of color, precipitation, effervescence, or other characteristics, are called reagents.

They are divided into general and special reagents; those denominated general, are employed to determine the class or group to which the substance under examination belongs; those termed special, are used for the detection of individual bodies. For the sake of clearness and simplicity, these two classes are subdivided as follows

:

REAGENTS IN THE HUMID WAY.

I. GENERAL REAGENTS.

a.-Reagents used as simple solvents.

b.-Reagents used as chemical solvents.

c.-Reagents used to separate, or otherwise characterize, groups of substances.

II. SPECIAL REAGENTS.

a.-Reagents used for the detection of bases.

b.-Reagents employed for determining the presence of acids.

REAGENTS IN THE DRY WAY.

FLUXES AND BLOWPIPE REAGENTS.

Each reagent will now be considered according to the plan thus laid down.

REAGENTS IN THE HUMID WAY.

I. GENERAL REAGENTS.

a. Reagents used as simple solcents.
1. DISTILLED WATER. HO.

Uses.-Principally as a simple solvent for a great variety of substances. It also effects the transformation of several neutral metallic salts into soluble acid and insoluble basic compounds; this is particularly the case with antimony and bismuth, which are precipitated in the form of a white powder, on the addition of much water. Tartaric acid readily dissolves or prevents the formation of the basic salt of antimony, which is thus easily distinguished from bismuth.

Tests. It should not leave the slightest residue upon evaporation; neither should it alter the color of blue or red litmus, or any other test-paper. Nitrate of silver, chloride of barium, oxalate of ammonia, or lime-water must not cause the least turbidity.

2. ALCOHOL. C1 H6 O2 = Ae O, HO.

There are two kinds; absolute alcohol, which, at 60° Fahr., should have a specific gravity of 796 or 797, and spirit of wine having a density of from 830 to 840 at the same temperature.

Uses. It is frequently employed for separating the substances soluble from those which are insoluble in it; as, for instance, chlorides of barium and strontium, the latter being dissolved by this menstruum.

It serves likewise to precipitate bases insoluble in it from their aqueous solutions, exempli gratia, malate of lime.

Alcohol is used also for the production of acetic and other ethers; to co-operate with acids in the reduction of chromic acid, peroxide of lead, et cetera; for detecting various substances

which impart a characteristic tint to the flame, especially boracic acid and strontia, and for detecting potassa combined with silicic acid, which, before the Blowpipe alone, gives the same reaction as soda or lithia.

Tests. Pure alcohol will completely volatilize, and neither causes any smell of fusel oil, when rubbed between the hands, nor reddens blue litmus paper.

Ether is little used for the analysis of inorganic bodies. It is principally employed for dissolving bromine, when isolated by other reagents, and for this purpose the commercial article is sufficiently strong and pure.

b. Reagents principally employed as chemical solvents.

1. HYDROCHLORIC ACID. H Cl.

Uses. It is very extensively used as a solvent, and for the detection of silver, suboxide of mercury, lead, and ammonia.

From solutions of the three former, it precipitates chloride of silver, subchloride of mercury, and chloride of lead, all of which are white. The chloride of silver is insoluble in nitric acid, but easily soluble in ammonia; the subchloride of mercury blackens on the addition of ammonia; and the chloride of lead is soluble in a large proportion of water.

When a glass rod moistened with dilute hydrochloric acid is brought into close contiguity with a solution containing free ammonia, white dense clouds of chloride of ammonium are formed.

Tests. When intended for analysis, it must be colorless, and leave no residue upon evaporation. Chloride of barium should produce no precipitate, neither in the highly diluted acid, nor after ebullition with nitric acid. Sulphide of hydrogen must leave it unaltered. After neutralizing with ammonia, and acetic acid has been added in slight excess, ferrocyanide of potassium must not produce any precipitate, nor even impart to it the slightest tinge of blue.

2. NITRIC ACID. HO, N 05.

Uses.-Nitric acid is employed as a solvent for metals, oxides, sulphides, et cetera. Metals, or sulphides, in dissolving, are first converted into oxides, and subsequently into nitrates. This acid dissolves most oxides, forming with them nitrates; the same occurs with most combinations of insoluble salts, the weaker acids being expelled by the nitric acid in the process of solution.

Nitric acid is used frequently as an oxidising agent, as to convert the oxide of iron into the sesquioxide, et cetera.

Tests. When pure, it is colorless, and leaves no residue when evaporated to dryness on platinum foil. Chloride of barium, or nitrate of silver must not in the least impair its clearness. Before adding these reagents, the acid should be slightly diluted, otherwise nitrates will be precipitated.

3. NITRO-HYDROCHLORIC ACID, AQUA REGIA. NOo Cl3.

Is generally prepared when wanted, by adding one part of pure nitric acid to two of hydrochloric acid. When kept for any length of time it decomposes.

Uses.-Principally as a solvent for gold and platinum.

4. ACETIC ACID. CH4 04-Ā.

Uses. This acid possesses a greater solvent power for certain substances than others, and is accordingly used to separate the former from the latter, as, for distinguishing oxalate of lime from phosphate of lime, the latter being easily dissolved, while the former remains unaltered. This reagent is also used for acidulation when it is necessary to avoid the presence of mineral acids.

Tests. It must leave no residue when evaporated upon platinum foil. When diluted, sulphide of hydrogen should cause no precipitate; nitrate of silver or chloride of barium should not render it turbid. Should the latter reagent cause a precipitate when the acetic acid has been boiled with pure nitric acid, sulphurous acid is present.