The primary constituent of whisky is ethyl alcohol, but the characteristic flavour is due to small quantities of by-products or "secondary constituents" produced during the processes of malting, fermentation, distillation, and maturing. These secondary bodies fall into the groups of acids, aldehydes, esters, and higher alcohols which are ordinarily estimated in analyses; but, in addition, there are other substances present which quite probably affect the aroma of the spirit. Thus Schidrowitz and Kaye,1 examining new pot-still whisky, obtained distinct evidence of the presence of pyrrol, phenolic bodies, an alkaline substance (probably an ammonium salt), hydrogen sulphide, and sulphur dioxide in different whiskies. They had also reason to suspect the presence of traces of nitriles, but did not obtain a positive identification. It was presumed that these various bodies, so far as they are products of dry distillation, were derived from the peat and coke used in malting, or from the action on the malt of the hot gases of the malt-kiln. Small quantities of volatile nitrogenous bases may also be present. Moreover, small amounts of sugars, acids, and colouring and extractive matters derived from the storage-vessels may exist in whisky, as well as added colouring matter.

As regards the nitrogenous bodies, Schidrowitz found the following. proportions present in twenty samples examined by the method given below: -

1 J. Soc. Chem. Ind., 1905, 24, 585.

Nitrogen compounds in whisky.

Scotch whiskies (new).

Grams per 100 litres absolute alcohol. (Calculated as NH,.)

Highland Malts (6 samples) ...............................

0.09

to

0.19

Lowland „ (3 „ ). ...............................

0.11

"

0.30

Campbeltowns (2 ,, ).................................

0.08

"

0.14

Grains (6 „ )...............................

0.03

"

0.14

American rye whiskies (matured) (3 samples)

0.26

"

0.39