One other possible contamination of water must be noticed : it is lead. Fortunately for most reasons, but unfortunately for seine others, water that contains an appreciable quantity of salts does not, as a gene ral rule, act upon lead. Pure distilled water acts very rapidly upon it, but water that is in any degree hard does not usually affect it. Lead can be easily detected iu water by the blackening which occurs on passing sulphuretted hydrogen gas through the water. This effect is not, however, produced if only a very small quantity of lead be present. In that case the water, after the presage of the gas, should be set aside for twenty-four hours, when the sulphuretted hydrogen will have become decomposed, and the deposited sulphur will have a dark-brown or black colour if lead be present. It has been suggested to tin the inside of lead pipes—water not acting upon tin ; but wherever water comes in contact with both metals, as at a joint or flaw, a voltaic action ie act up, and the solution of the lead is facilitated instead of prevented.
Estimation of Water.—This is accomplished either by noting the loss which a body suffers on being heated, or by expelling and weighing the water evolved. If the constitution of the body is well known, the former method is sufficient ; if not the latter process is had recourse to.
Analysis of Norma/ and Abnormal Wafers—Of all special chemical operations this is one of the most tedious and difficult. Usually a large number of acids and bases are simultaneously present, and being all in solution, cannot be so readily separated as those of perhaps a less complex substance containing both soluble and insoluble matters.
Gaseous constituents must generally be determined at the source of the water. The total amount of fixed matter is ascertained by evapo rating a known bulk of the water, and weighing 'the residue after drying at 212' Fehr. If organic matter be present, the residue, dried at 300° Fehr., will char on being ignited ; air having access, the carbon will burn off', and the difference in weight, before and after ignition, will give some idea of the amount of that organic matter. The residue may then be quantitatively analysed in the same manner as any other mixture of solids, or separate portions of the water may be used for the purpose. The arrangement of the results of a water analysis depends upon the judgment of the operator. The actual amounts of each ingredient, without reference to arrangement, should first be given, inasmuch as the state in which they naturally exist is liable to alteration from change of temperature and dilution after rain, &c. Moreover, as there are at present no data by which to determine the normal condition of the acids and bases, several systems of arrange ment exist ; and if the amount of each acid and base were not given, the analyses of a water by two different chemists would appear to differ widely when, perhaps, they closely agree.