solution of ammonia, in such a manner that the reaction of the new compound is rather slightly alkaline than acid.

Uses. This reagent serves to separate peroxide of iron from oxide of manganese, and other metallic oxides.

4. WATER OF BARYTES.

5. CARBONATE OF LIME.

Preparation. Precipitate a heated solution of pure chloride of calcium with carbonate of ammonia, to which a little caustic ammonia has been added; allow the precipitate to subside; wash it carefully, and keep the pappy mass thus obtained in a close vessel for use.

Uses. This reagent serves particularly to separate peroxide of iron from other metals which are not precipitated by carbonate of lime.

6. CARBONATE OF BARYTES.

Preparation. This reagent is prepared from chloride of barium in the same manner as the preceding substance is prepared from chloride of calcium.

Uses.-Carbonate of barytes is used for the same purposes as carbonate of lime; but it is in many cases preferable to the latter.

7. PROTO-SULPHATE OF IRON.

8. PEROXIDE OF MERCURY.

This re-agent serves, in quantitative investigations, principally to decompose chloride of magnesium, in the process of separating magnesia from the alkalies.

9. PERCHLORIDE OF MERCURY. 10. PROTO-CHLORIDE OF TIN.

11. PERCHLORIDE OF GOLD.

12. CHLORIDE OF PLATINUM.

13. HYDROFLUO-SILICIC ACID.

14. TARTARIC ACID.

15. SULPHUROUS ACID.

16. COPPER.

The copper of commerce (with the exception of Japanese copper, which it is not always easy to procure) is not sufficiently pure for most analytical purposes.

The most convenient mode of preparing pure copper is that recommended by Fuchs; it consists in precipitating solution of blue vitriol with a piece or blade of clean iron; freeing the precipitated copper from the iron by boiling with hydrochloric acid, washing, drying, and fusing. The metal thus obtained is to be rolled out into thin sheets.

Tests. Pure copper must dissolve perfectly in nitric acid, and this solution must not yield the slightest trace of a precipitate upon addition of ammonia in excess, even after long standing, (iron, lead, etc.); nor should the addition of hydrochloric acid render it turbid (silver). Sulphuretted hydrogen must precipitate the copper completely from this solution.

Uses. This metal is frequently applied for the purpose of indirect analysis; thus, for instance, we use it to determine the amount of copper present in a fluid, or the amount of protoxide of iron existing by the side of the peroxide, etc.

17. TIN.

Preparation. Malacca tin, or English-grain-tin, is fused and poured out into slips. In cases where this cannot be readily procured, pure peroxide of tin is reduced by means of cyanide of potassium; the peroxide intended for this purpose should be prepared by oxidizing common tin with nitric acid, and washing, first with water containing a slight admixture of hydrochloric acid, and subsequently with pure water.

Tin is employed exclusively in the process of separating antimony from tin; it may be considered fit for that purpose if it dissolves in hot hydrochloric acid, forming a perfectly clear

solution.

b. Reagents which serve principally to determine, or to separate,

acids.

$ 38.

1. ACETATE OF POTASS.

2. CHLORIDE OF CALCIUM.

3. FLUORIDE OF CALCIUM.

This substance is used in quantitative analysis to expel and determine boracic acid; perfectly pure fluor spar, (like that of Derbyshire,) free from any admixture of silicic acid, is applicable for this purpose. Hydrofluoric acid, which is used in analytical investigations for the decomposition of silicates, may be prepared from a less pure kind of fluor-spar than the Derbyshire.

Tests. The best way of testing the purity of fluor-spar, in case of doubt, is to analyse it; the analysis is effected by levigating the fluor-spar finely, and treating a weighed amount of it with pure concentrated sulphuric acid, in a platinum crucible, at a gentle heat, which is gradually increased to redness :—this operation is to be repeated until the residue remains constant. The fluor-spar may be considered pure if the calculated amount of gypsum is obtained.

4. CHLORIDE OF MAGNESIUM.

5. PERCHLORIDE OF IRON.

6. OXIDE of lead.

7. NEUTRAL ACETATE Of lead.

8. PROTOCHLORIDE OF PALLADIUM.

Preparation.-Dissolve palladium in aqua regia, evaporate to dryness, to expel the excess of acid; dissolve the residue in 20 parts of water, filter, if necessary, and keep the brown solution for use. This solution will contain a slight admixture of perchloride of palladium, which, however, is unimportant in the precipitation of iodine, the only purpose for which we use this reagent.

9. PROTOCHLORIDE OF ARSENIC.

Preparation.-Dissolve vitreous arsenious acid in pure and hot hydrochloric acid, and keep the solution for use.

Uses. This reagent is employed for the determination of sulphuretted hydrogen.

B.-REAGENTS IN THE DRY WAY.

§ 39.

1. CARBONATE OF SODA.

2. HYDRATE OF BARYTES.

3. ACID SULPHATE OF POTASS.

Preparation.-Mix 87 parts of neutral sulphate of potass with 49 parts of pure hydrated sulphuric acid, in a platinum crucible, and heat to gentle redness, until the mass is in a state of uniform and clear fusion. Pour the fused mass into a platinum or porcelain dish, standing in cold water. After cooling, break the mass into pieces, and keep the latter for use.

Uses. This reagent serves to resolve certain compounds of alumina, and of oxide of chromium, occurring in nature.

4. NITRATE OF POTASS.

5. CARBONATE OF AMMONIA, (solid).

Uses.-This reagent serves to convert the acid sulphates of the alkalies into neutral salts.

6. BIBORATE OF SODA-BORAX, (fused).

Preparation.-Heat crystallized borax in a platinum or porcelain dish, until it ceases to swell; reduce the porous mass to powder, and heat the latter in a platinum crucible, until the whole is fused into a transparent mass. Pour the more fluid portion of this mass upon a porcelain dish, remove the rest from the crucible by means of a platinum spatula, and keep the borax glass thus obtained in a stoppered bottle.

Uses. This reagent serves to expel carbonic acid, and other volatile acids, at a red heat.

7. HYDROGEN GAS.

Preparation.-Hydrogen gas is evolved from dilute sulphuric acid by means of granulated zinc. It may be procured absolutely pure by transmitting it, in the first place, through a long glass tube loosely filled with cotton, soaked with solution of perchloride of mercury; subsequently through potass ley; and finally through hydrated sulphuric acid. In most cases, however, it is only necessary to transmit it through sulphuric acid, or through a chloride of calcium tube, for the purpose of drying it.

Tests.-Pure hydrogen gas is inodorous. It ought to burn with a colorless flame, which, when cooled by depressing a porcelain dish upon it, must deposit nothing on the surface of the dish except pure water, (free from acid re-action).

Uses.-Hydrogen gas is frequently used in quantitative analysis, to reduce oxides, chlorides, sulphurets, etc. to the metallic

state.

8. CHLORINE.

Chlorine gas is purified and dried by transmitting it, first, through a washing bottle, containing concentrated sulphuric acid, and, finally, through a chloride of calcium tube; the latter may, however, be omitted.

-Uses.-Chlorine gas serves principally to produce chlorides, and to separate the volatile from the non-volatile chlorides; it is also used to expel, and indirectly to determine, bromine and iodine.

C.-REAGENTS APPLIED IN ORGANIC ELEMENTARY ANALYSIS.

§ 40.

1. OXIDE OF COPPER.

Preparation.-Mix pure copper scales with pure nitric acid, in a porcelain dish, so as to form a thick paste; after the effervescence has ceased, heat gently in the sand-bath until the mass is perfectly dry. Transfer the green basic salt produced into a hessian crucible, and heat to moderate redness, until no more