The "Spiritus Rectificatus" or "Alcohol (90 per cent.)" of the British Pharmacopoeia is defined as "a mixture of ethyl hydroxide and water, containing in 100 parts by volume 90 parts by volume of ethyl hydroxide, C2H5OH. Specific gravity 0 8337. Contains 85.68 per cent. by weight of ethyl hydroxide, and 1432 per cent. by weight of water." The analytical tests of purity are given in Chap. VI.

1 Pharm. J., 1918, 100, [iv], 127.

It should be noted that on account of the contraction which occurs, 'Alcohol (90 per cent.)" would not be given by mixing 90 volumes of (true) absolute alcohol and 10 volumes of water.

There are four official "Diluted Alcohols" in the Pharmacopoeia, containing respectively 70, 60, 45, and 20 per cent. of ethyl hydroxide by volume. They are obtained by diluting the 90 per cent. alcohol of sp. gr. 0 8337 with water as shown in the following table, either (1) or (2) being used, as may be the more convenient: -

Alcohol required.

Sp. gr.

(1).

(2).

Volume of water to be mixed with

1 litre of 90 per cent. alcohol.

Vol. of 90 per cent. alcohol to be diluted to

1 litre at 15.5°.

70

per cent.

0.8899

310.5

c.c.

777.8

c.c.

60

"

0.9134

536.5

"

666.7

"

45

"

0.9435

1053.4

"

500.0

"

20

"

0.9760

3558.0

"

222.2

"