Apart from the usual method of estimation by means of the specific gravity and appropriate tables, which is dealt with at length in the chapter on "Alcoholometry," there are various other physical processes whereby the proportion of alcohol in an aqueous solution can be deduced. Some of the more interesting of these are described below. A passing reference will suffice for several of them, as they have no practical application - except possibly in occasional special circumstances.

Brewster's "staktometer" or drop-measurer is in the form of a bulbed pipette with a finely-tapering delivery tube. Filled with water, and then allowed to empty itself, it does so in a certain number of drops, which are counted. Filled with alcohol, and allowed to discharge similarly, the number of drops is much greater; it varies, in fact, according to the strength of the alcohol. Thus with a particular instrument distilled water gave 734 drops, and aqueous-alcohol of specific gravity 0920 gave 2,117 drops. By constructing a table of the number of drops required for different proportions of alcohol, the instrument can therefore be used to ascertain alcoholic strengths.

Geissler's vaporimeter is designed to give the percentage of alcohol in a liquid by measuring the vapour pressure of the liquid. The lower end of a barometer tube is bent twice at right angles. At the extremity, which now points upwards, is fitted a stopcock, and also a detachable bulb. In this bulb the spirit is placed. The tube being charged with mercury, the bulb containing the alcohol is re-attached, the stopcock opened, and the alcohol vaporised by heating the bulb with hot water. A graduated scale on the tube shows the height to which the mercury is forced by pressure of the alcohol vapour, and the corresponding alcoholic strength is given by tables constructed for the instrument.

Dilatometers have also been devised for measuring percentages of alcohol by means of the expansion shown when a definite volume of the liquid is raised from one fixed temperature to another. The amount of expansion varies with the proportion of alcohol in the liquid (Silbermann).

Potassium carbonate, added in sufficient quantity to aqueous solutions of alcohol, absorbs the water and causes the alcohol to separate out. If the liquid is contained in a long glass tube fitted with a graduated scale, the volume of the alcohol layer can be read off. The scale is calibrated by experiments with alcohol solutions of known strength (Brande). For rough purposes, an ordinary stoppered glass graduated cylinder can be used.