What is usually referred to as the "alcohol" of ordinary potable spirits does not consist merely of pure ethyl alcohol. Small quant ties of associated by-products, especially higher alcohols, esters, aldehydes, and acids, are present with the ethyl alcohol; and upon the nature and proportion of these by-products depend the special flavour and character of the spirit. Ethyl alcohol alone would give a relatively featureless spirit, apart from its properties as an intoxicant. The differences in flavour between brandy, rum, and whisky, and also - equal alcoholic strength being postulated - any differences in physiological effects which they may show, depend upon the by-products developed during the manufacture of these spirits, in so far as these by-products are retained in the finished articles. Furthermore, the differences in character between various specimens of the same class of spirits - whisky, for example - are, other things being equal, due to variations in the character or amount of the by-products or "secondary constituents," as they are generally called. A "pot-still ' whisky contains more of these than a "patent-still " spirit.

In fact, the modern patent still rectifies the spirit so thoroughly that only a small quantity of the secondary constituents may remain. Hence such spirit is known as "neutral" or "silent' spirit. It is also often referred to as "grain" spirit, from the fact that unmalted grain, as distinct from malt, is largely used to supply the wash distilled for making potable spirits in patent stills.

As it is made from cheaper materials and by more effective plant, patent-still spirit is cheaper to produce than the pot-still variety. Hence there is a temptation to substitute it for the latter kind in some case3. It is not to be assumed, however, that this is necessarily done with fraudulent intent, especially where whisky is concerned. Many people prefer a milder blend of the two kinds to the stronger-flavoured pot-still variety alone. Nevertheless, it is often necessary to know what is the character of a given specimen of spirits from this point of view - namely, as to whether it consists wholly of pot-still spirit, or of patent-still spirit, or of a mixture of the two.

The chemical analysis of potable spirits is not always sufficient to decide questions which may arise as to the genuineness of the spirits or the correctness of the designation under which they are sold. Our knowledge of some of the constituents is imperfect, our methods of determining others not very satisfactory; and, above all, the articles themselves vary, and legitimately vary, within certain limits. Notwithstanding this, chemical analysis, as remarked by the Royal Commission on Whisky,1 "is capable of affording very important assistance in many, if not in all, cases of suspected misdescription, when the results of analysis are taken in conjunction with other evidence such as that of the expert taster." Needless to say, there are many cases in which chemical analysis is capable, not only of " affording assistance," but of showing positively whether a spirituous article is or is not what it purports to be.

The analysis usually comprises the following determinations: -

(1) Alcoholic strength.

(2) Acidity, fixed and volatile.

(3) Total solids and ash, with further examination of these when necessary as regards colouring-matters, sugars, metallic compounds, etc.

(4) Character of the distillate, in respect of the proportions of secondary constituents: -

(a). Volatile acids.

(6). Esters.

(c). Furfural.

(d). Aldehydes other than furfural.

(e). Higher alcohols.

Except as regards this last item, most analysts use substantially the same processes for making the respective determinations. Several different methods, however, are employed for estimating the higher alcohols. It will therefore be convenient to describe first of all the operations for the other constituents, leaving the higher alcohols for separate discussion. The processes adduced below are those in use at the Government Laboratory, essentially as given in evidence to the Royal Commission on Whisky.1

1 Final Report, Cd. 4796, p. 47.