124

DYEING AND CALICO PRINTING.

sulphuric acid with about n or 12 parts of water, and stir the whole well. Themixture having become quite cold, fill the alkalimeter with the cold dilutedacid up to the point marked 0°, taking the under line of the liquid as the truelevel, and, whilst stirring briskly the aqueous solution of the 53 grs. of car-bonate of soda, pour the acid carefully from the alkalimeter into the vortexproduced by stirring, until, by testing the liquor alternately with reddenedand with blue litmus paper, or, more conveniently still, with grey litmus paper,the neutralising point is exadlly hit.” This acid may be termed simplynormal sulphuric acid, and every 100 alkalimetrical degrees, or 1000 water-grains’ measure of it, contain 1 equivalent or 40 grs. of anhydrous sulphuricacid, capable of saturating or neutralising 1 equivalent or 47 grs. of potash,31 of soda, 28 of lime, 17 of ammonia, and indeed an equivalent of any otheralkaline base.

For further detail as to the preparation of reagents in a state of chemicalpurity for more delicate estimations than are required in commerciallaboratories, the reader should refer to works of scientific research.

Normal Oxalic Acid Solution.

Mohr was the first to substitute oxalic acid for sulphuric acid in the de-termination of the value of carbonated and caustic alkalies. It is similar inits adtion upon litmus; and it can be readily and accurately weighed in a drystate. Mohr recommends that the solution be prepared by dissolving 63 grms.of oxalic acid perfectly dry but not effloresced in a litre of water, while asolution of caustic potash is so adjusted that, bulk for bulk, it neutralisesthe acid, 6'gii grms. of potash or 5'32 grms. of soda should be weighed out,these quantities corresponding to 0^05 of a molecule; so that as 1000 c.c. ofthe test acid contain a half molecule of oxalic acid, 100 c.c. will exaftlyneutralise the quantity of alkali. The oxalic acid solution is added to thealkaline solution to be tested with an excess of 5 to 6 c.c.; by this excessthe litmus is turned a wine-red. By means of a pipette divided into tenthsof a cubic centimetre the alkaline solution is added until the litmus is againcoloured blue. The number of c.c. of test acid employed, minus the numberof c.c. of alkali employed, gives the percentage of pure carbonate of potash.Thus, if the sample weighed out were 6'go grms. of the potash, and72 c.c. of the acid and 6 c.c. of the alkaline liquor were employed,72 — 6 = 66 per cent of carbonate of potash.

Normal Hydrochloric Acid Solution.

A normal solution of hydrochloric acid contains 36’5 grms. of chemicallypure hydrochloric acid in 1000 c.c. of distilled water. 1 c.c. of the normalacid then contains o - 036 grm. of hydrochloric acid.

Normal Nitric Acid Solution.

A normal solution of nitric acid contains 54 grms. of chemically pure nitricacid in 1000 c.c. of distilled water. 1 c.c. of the normal acid, then, contains°'°54 grm. nitric acid.