Creosote gives a blue colour with ferric chloride solution; and the exceedingly pungent vapours evolved upon heating a residue containing capsicum are equally characteristic. The presence of tannin in distilled spirits, which is mostly derived from their preservation in casks, is recognised by the formation of a bluish-black colour upon the addition of ferric solutions. The identification of the various ethylic and amylic ethers used in the preparation of factitious liquors is a matter of some difficulty. Their presence is most readily detected by means of their characteristic odour, which is developed upon adding a little sodium hydroxide to the sample, evaporating the mixture over the water-bath almost to dryness, and then adding a small quantity of sulphuric acid. Another means of ascertaining the nature of the organic ethers present in spirits is to first remove the ethylic alcohol contained by a partial distillation with an alkaline solution, and then acidulate the remaining liquid with sulphuric acid, and repeat the distillation, when the volatile fatty acids originally contained in the ethers will be found in the distillate; their identity is to be established by means of their characteristic properties. Nitrous ether (which compound is not contained in genuine liquors) may be detected by partially distilling the sample and adding a mixture of potassium iodide, starch paste, and acetic acid to the first portion of the distillate, the production of a blue colour indicating its presence. As previously remarked, the exercise of the ordinary senses is frequently of greater value in judging the quality of liquors than the results of chemical tests. Many of the organic ethers employed in the manufacture of artificial liquors are identical with those contained in the genuine article, and it is obvious that, in such instances, no distinction can be made between them.
WATER.
The subject of the purity of potable waters possesses the highest degree of importance in its sanitary relations, and, particular attention has been bestowed upon methods of analysis that would serve to indicate the character and significance of existing impurities. The earlier processes of examination, which chiefly consisted in the determination of the mineral constituents of water, while of use in furnishing an idea of the general nature of the water regarded as an inorganic solution, almost totally failed to reveal the presence of the more subtle and important organic contaminations which are now known to exert an active influence in the propagation of zymotic diseases. During the past few years, decided progress has been attained in the analytical methods employed. Little is known of the exact nature of the organic constituents present in water that has received sewage contamination. They may be either of vegetable or animal origin, and it appears to be very probable that they constitute organised germs. But, although we are still unable to determine the constitution of these deleterious ingredients, it is at present possible to approximately ascertain the hygienic character of drinking water, and to distinguish, with a fair degree of accuracy, between a good and a bad sample. In arriving at a conclusion regarding the sanitary quality of water, it is, however, also needful to take into consideration the origin and surrounding conditions which affect the chances of contamination. Most of the more recent methods of water analysis are based upon the fact, that the putrefactive decomposition of harmful organic matter is attended by the genesis of certain compounds (such as ammonia, nitrites, and nitrates), of which quantitative estimations can be made. For the purpose of ascertaining the character of a potable water, the following determinations are usually necessary:—
1. Colour, odour, and taste.
2. Total solid matter and loss on ignition.
3. Organic matter in solution.
4. Chlorine.
5. Ammonia, free and albuminoid.
6. Nitrogen, as nitrites and nitrates.