These constitute (such of them as can be procured) some of the most useful and most powerful chemical reagents in use. There is also another compound body, _cyanogen_, similar in its characters to a supporter: it also forms various acids, by uniting to hydrogen, chlorine, oxygen, sulphur, &c. Thus we have Hydrocyanic acid Chlorocyanic acid Cyanic acid Sulpho-cyanic acid, &c. We know, also, fluosilicic acid and fluoboric acids. If to these we add fulminic acid, and the various sulphur acids already investigated, we may state, without risk of any excess, that the number of acids at present known to chemists, and capable of uniting to bases, exceeds a hundred. The number of alkaline bases is not, perhaps, so great; but it must even at present exceed seventy; and it will certainly be much augmented when chemists turn their attention to the subject. Now every base is capable of uniting with almost every acid,[9] in all probability in at least three different proportions: so that the number of _salts_ which they are capable of forming cannot be fewer than 21,000. Now scarcely 1000 of these are at present known, or have been investigated with tolerable precision. What a prodigious field of investigation remains to be traversed must be obvious to the most careless reader. In such a number of salts, how many remain unknown that might be applied to useful purposes, either in medicine, or as mordants, or dyes, &c. How much, in all probability, will be added to the resources of mankind by such investigations need not be observed. [9] Acids and bases of the same class all unite. Thus sulphur acids unite with sulphur bases; oxygen acids with oxygen bases, &c.