The product of the pot-still, as stated above, does not contain merely alcohol and water, but also, in intimate mixture or in solution, other matters yielded by the grain, and either previously exi.ting in it or formed during the processes of fermentation and distillation. These are present chiefly in the form of volatile oils and vegetable acids, and their quantity as well as their nature depends upou the quality of the grain, and the amount of care bestowed upon the fermentation and other subsequent processes. The finest Dublin whiskey, when made, is stored in large casks, at a strength of 25 per cent. overproof. During its sojourn in the cask, the reactious which occur between the above substances, and the alcohol itself lead to the gradual formation of those fragrant volatile ethers which impart to the spirit its characteristic perfume and flavour. It attains its full maturity and highest excelleuce at an age of from three to five years in the wood ; after this period, it may be bottled and preserved for an indefinite length of time without undergoing further change.
Owiug to the reputation enjoyed by whiskey of an Irish, or Dublin manufacture, au enormous quantity of both Scotch and English silent spirit finds its way to Dublin or Belfast, in order that it may be falsely palmed off upon purchasers, under cover of an Irish permit, as Irish whiskey. Genuine whiskey ie put generally into old sherry casks, by which means a slight flavour and colour are afforded to it. Large quantities of an inferior sherry, known as " Hamburgh Sherry," arc also employed in effecting the conversion of silent spirit iuto whiskey. The actual composition of this " sherry " is not known, except hy those who make it, but there is no evidence to show that it is harmful. The process known as "blending" is largely resorted to for the purpose of introducing silent spirit into the market under the name of whiskey. In order to effect this, it is the custom to mix a quantity of coarse, ncw, strongly-tasted, genuine pot-still whiskey with an equal quantity of silent spirit, the value of which is about one-half that of the former kind, and to sell tho mixture as old Irish whiskey. On account of the strong taste of the former spirit, and the absolute tasteless ness of the latter, the effect of mixing the two is to produce a spirit which is much milder than the gcnuino Irish spirit employed, and which may he represented to the consumer as being of greater age and better quality than it really is. This practice has been so widely carried on that enormous quantities of new whiskey, containing fusel-oil and other impurities, which in course of time would have undergone beneficial changes, have been consumed as oid spirit simply through being diluted with silent spirit. It is possible, however, to distinguish readily between the two varieties. Genuine whiskey of mature ago has an exquisite perfume, aud when freshly opened soon fills the room with its fragmnce. A few drops rubbed upon the palms of the hands retain their fragrance until completely evapomted ; whereas, the odour left by silent spirit, or counterfeit whiskey, when submitted to the same test, is of a decidedly unpleasant nature (see Alcohol from Gmin).
volatile, mobile fluid, discovered by Dobereiner, who obtained it in an impure state, and named it light oxygen titer. It was afterwards prepared in a pure state by Liebig, who also demonstrated its constitution and properties.
The coroposition of aldehyde may be represented by that of alcohol after the abstraction of two atoms of hydrogen ; then alcohol being represented by the formula C211,0, that of aldehyde is C21140 ; the word " aldehyde " itself is an abbreviation of "alcohol dehydrojenatum." Aldehyde con stitutes an intermediate stage in the oxidation of alcohol into acetic acid, and is produced by the destructive distillation of alcohol, and many other organic compounds. There are very many methoda by which aldehyde rnay be prepared, the following, by Liebig, being the best :—Two parts of 80 per ceut. alcohol are mixed with two parts of water, three parts of peroxide of manganese, and three parts of oil of vitriol, and the mixture is introduced into a capacious retort fitted with a receiver, which is kept constantly cool. The contents arc heated gently until they begin to froth, and the distilla tion ia arrested when the receiver contains about one-third, and the distillate begins to redden litmus. When this is the case, it is mixed with its own weight of chloride of lime and redistilled until part has been obtained ; this product is treated in the same way, and the distillate, amountiog to about part is mixed with twice its volume of ether, and saturated with dry ammonia gas. The crystals of aldehyde-ammonia obtained are washed with ether and dried ; two parts are then dissolved in water, aud a mixture of three parts of sulphuric acid with four parts of water is added ; the whole ie next distilled at a low heat, on the water-bath, and the vapoUrs of aldehyde are condensed in a receiver surrounded with ice, after being dehydrated by passing over chloride of calcium.
Aldehyde is a thin, colourless fluid ; it is very inflammable, burning with a pale, bluish flame. Its specific gravity is 0.800, and its boiling point 21°, It possesses a very pungent odour, mixes in any proportion with water, alcohol, and ether, and readily dissolves iodine, sulphur, and phosphorus. Aldehyde combines with aniline, forming a brilliant violet colouring matter dis covered by Charles Louth. It is prepared artificially in an impure state for this purpose.
The word aldehyde seems now to signify any compound which yields an alcohol by taking up two atoms of hydrogen, or an acid by taking up two atoms of oxygen. Some compounds which are classed as " aldehydes " (for this reason), enter largely into the composition of various essential oils, such as those of bitter almonds, cinnamon, rue, &c., and, with the knowledge of this fact, it may be possible to prepare these oils artificially on a large scale.