2 Historical Sketch of Improvements in [July, 



The mineral kingdom contains a much smaller number of spe- 

 cies than either the vegetable or the animal. The substances of 

 which it is composed are of such a nature that they admit of a 

 much easier investigation than those of which vegetables and 

 animals are composed. The consequence is, that very consider- 

 able progress has been made in ascertaining their nature and 

 constitution. The greater number of minerals possess the 

 characters of salts containing some one or more of the salifiable 

 bases united to about 10 acids, one or more of which occur in 

 almost every stone. Now when the mineral happens to be a 

 ■compound of a single acid and a single base mutually saturating 

 each other, there is no great difficulty in determining its compo- 

 sition, and accordingly such minerals may be considered as 

 sufficiently well known. Calcareous spar, sulphate of ha7ytes, 

 moli/bdate of lead, may be given as examples. The first of these 

 is a compound of one atom of carbonic acid and one atom of 

 lime, the second of one atom of sulphuric acid + one atom of 

 barytes, and the third of one atom of molybdic acid and one atom^ 

 of oxide of lead. Of such simple and well-defined species, a 

 considerable number occur in the mineral kingdom. They are of 

 easy investigation, and their composition may be considered as 

 pretty accurately determined. But a great many minerals are of 

 a more complicated nature than these. They either contain one 

 acid united to two or more bases, or they contain at once several 

 acids and several bases. Thus, for example, felspar is a com- 

 pound of silica (acting the part of an acid) and potash and 

 alumina (acting the part of bases). In such cases it is much 

 more difficult to determine the true composition of the mineral, 

 ^and the way in which the various constituents are combined. 

 Accordingly very little progress has hitherto been made in these 

 investigations. The simple salts (by this term, 1 mean salts 

 composed of one acid and one base) may be decomposed and 

 made again at pleasure. We can produce exact imitations of 

 them in our laboratories ; but we cannot, in the same way, pro- 

 duce any thing exactly similar to the more complex minerals.. 

 Now till this be done it cannot be said that we have made any 

 considerable progress in the investigation of these complex 

 minerals. 



It is not in our power to unite together artificially the consti- 

 tuents of any one vegetable or animal substance so as to make 

 a body exactly similar in its nature and properties ; so that we 

 ■cannot say that at present we are acquainted with the composi- 

 tion of a single animal or vegetable substance. It is true that 

 we have it in our power to induce certain changes in vegetable 

 substances, and by that means to convert them into certain 

 other substances possessed of quite different properties. Thus 

 when the juice of an onion is fermented, a quantity of manna 

 makes its appearance in it, which did not exist in it before. 

 When starch and sulphuric acid are boiled together with a suffi- 

 cient quantity of 'ivater, the starch is converted into a saccharine 



