The per-centage by weight may be converted into per-centage by volume, by multiplying the former by the sp. gr. of the sample, and dividing the product by the sp. gr. of absolute alcohol. This is merely the reverse of the operation described above. _Obs._ The preceding methods of alcoholometry, as well as all others depending on the sp. gr. refer to UNSWEETENED SPIRITS only; and are inapplicable to those holding sugar in solution, or any other organic matter capable of altering the sp. gr. For sweetened spirits, fermented worts, wine, beer, &c., one or other of the following processes must be adopted:—— 3. Other methods, adapted to either SWEETENED or UNSWEETENED SPIRITS, Tinctures, Fermented Liquors, &c.—— _a._ By DISTILLATION as originally proposed by M. Gay-Lussac. 300 parts of the liquor under examination (measured in a graduated glass tube) are placed in a retort or small still, and a quantity exactly equal to one third (_i.e._, 100 parts), carefully drawn over; a graduated glass tube[13] being used as a receiver, and the operation stopped as soon as the distillate reaches the hundredth degree. The ‘alcoholic strength’ of the distilled liquor is then ascertained by any of the usual methods, and the result divided by three, when the per-centage of alcohol in the original liquor is at once obtained. If, from want of attention, more than 100 parts should be distilled over, the number which expresses the relation of the volume of the distilled product to the original bulk of the liquor tested, must be employed as the divisor. Thus, if 106 parts of liquor have distilled over (instead of 100), containing 33% of alcohol, the 300 must be divided by 106, which gives 2·83, and the 33% by this 2·83, which gives 11·66%, the true proportion of alcohol in the original liquor. The strength at ‘proof’ may be calculated from this in the usual way. [Footnote 13: Mulder, in his ‘Chemistry of Wine’ recommends this receiver to be shaped like a bottle, with its neck, or tubular part, bent at right angles above the line of its scale; and that it should be set in the centre of a glass jar kept filled with very cold water.]