One hundred c.c. of the sample, or the residue left in the distilling flask from the distillation experiment mentioned below, are evaporated to dryness in a tared capsule, dried in a steam oven at 100°, and weighed after cooling in a desiccator. The residue is then ignited at a dull red heat to obtain the ash, which after weighing is examined for the presence of lead, copper, iron, etc., if required.

Distillation

Commercial spirits are often slightly sweetened and coloured, usually with caramel, though sometimes with a coal-tar dye. Moreover, most such spirits contain colouring and other matters extracted from the cask in which they have been stored. Hence it is necessary to free the spirit from these colouring and extractive matters by distillation, before the tests described below can be applied. This practice is also advisable even when the spirit appears to be colourless.

The specific gravity and apparent strength of the sample having been ascertained, a measured quantity (120 to 150 c.c., or more, according to the strength) is placed in a distilling flask, diluted to nearly 200 c.c. with distilled water, and gently distilled to as near dryness as possible without charring the residue. The distillate is made up to 200 c.c. with water, and the alcoholic strength determined; it should be about 50 per cent. by volume (87.5 per cent. of proof spirit), and the quantity taken for distillation should have been such as to give this strength.

(Note

Some analysts prefer to complete the distillation by passing a current of steam through the residual liquid when it has been distilled down to a small bulk. See below, Allen-Marquardt method.)

1 Appendix Q, p. 17.

Examination of the Distillate.