PART IV.—ACIDS AND ALKALIES. 
SULPHURIC ACID—HYDROCHLORIC ACID—NITRIC ACID- 
ACETIC ACID—AMMONIA—POTASH—SODA—NEUTRAL 
SODIUM, POTASSIUM, AND AMMONIUM SALTS. 
I.—Sulphuric Acid. 
§ 57. Sulphuric acid (hydric sulphate, oil of vitriol, H 2 S0 4 ) occurs 
in commerce in varying degrees of strength or dilution ; the strong sul¬ 
phuric acid of the manufacturer, containing 100 per cent, of real acid 
(H 2 S0 4 ), has a specific gravity of 1-850. The ordinary brown acid of 
commerce, coloured by organic matter and holding in solution metallic 
impurities, chiefly lead and arsenic, has a specific gravity of about 
1-750, and contains 67-95 of anhydrous S0 3 = 85-42 of hydric sulphate. 
There are also weaker acids used in commerce, particularly in manu¬ 
factories in which sulphuric acid is made for special purposes without 
rectification. The British Pharmacopoeia sulphuric acid is directed 
to be of 1-841 specific gravity, which corresponds to 77 per cent, sul¬ 
phuric anhydride, or 86-8 per cent, of hydric sulphate. The British 
Pharmacopoeia lead limit is 20 parts per million ; arsenic limit, 5 parts 
per million. The dilute sulphuric acid of the Pharmacopoeia should have 
a specific gravity of 1-069, and corresponds to 10 per cent, of anhydrous 
hydric sulphate. Aromatic sulphuric acid, containing tincture of ginger, 
spirit of cinnamon, alcohol, and sulphuric acid, has a specific gravity of 
0-917-0 923 and contains sulphuric acid equal to 9-96 per cent. S0 3 . 
The general characters of sulphuric acid are as follows :—When 
pure, it is colourless, or, when impure, a dark brown to black, oily 
liquid, without odour at common temperatures, of an exceedingly acid 
taste, charring most organic tissues rapidly, and, if mixed with water, 
evolving much heat. If 4 parts of the strong acid are mixed with 1 
part of water at 0°, the mixture rises to a heat of 100° ; a still greater 
heat is evolved by mixing 75 parts of acid with 27 of water. 
Sulphuric acid is powerfully hygroscopic — 3 parts will, in an 
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