Five c.c. of the spirit are diluted to 50 c.c. with water in a glass cylinder of about 3 cm. internal diameter, and the opalescence produced is compared with that given by a standard mixture under the same conditions. The standard should be of approximately the same alcoholic strength as the sample, and is composed of plain spirit and wood naphtha in the proportion of 9 volumes to 1, together with known quantities of mineral naphtha. The proportion of the minsral naphtha is varied until the opalescence produced on dilution matches that of the sample under examination.

Esters

Ten c.c. of the spirit are carefully neutralised with decinormal soda solution after addition of two drops of phenol-phthalein indicator, then a further quantity of 20 c.c. of the soda solution is added, and the mixture heated for two hours in a silver pressure flask on the steam-bath - or, alternatively, boiled in a glass flask under a reflux condenser. The excess of alkali is then titrated with decinormal sulphuric acid. A " blank " experiment is made with 10 c.c. of water under the same conditions. Each cubic centimetre of N 10-soda used up in hydrolysing the esters in the sample represents 0 0074 gram of esters, calculated as methyl acetate.