Dictionary.net

• dilute alcohol with 40 to 50 per cent, of pure alcohol.

1898 - American pocket medical dictionary
By Willam Alexander Newman Dorland

• n. A. mixture of pure alcohol and water in the proportions by weight, of 100 parts of alcohol to 103:09 of water, and by measure, of 100 parts of alcohol to 81:82 of water.

1871 - The Cabinet Dictionary of the English Language