400 ON MINERAL VEINS. 



If chemistry has not yet formed every complicated 

 salt that is found in the list of metallic saline minerals, 

 it has produced so many, that we may, with little 

 hazard of error, consider the aqueous process as fully 

 competent to the production of the whole. That 

 Nature can exhihit some of them in a crystallized 

 form, such as the phosphat of iron, when we can ob- 

 tain them only in a powdery one, must he referred to 

 the cause just noticed: namely, the rapidity of our 

 operations and the slowness of hers. As to the silicats, 

 our acquaintance with the real nature of this com- 

 hination, or the exact mode in which silica acts the 

 part of an acid, is as yet so recent and imperfect, that 

 no opinion can at present be given respecting them. 



The igneous theory of metallic veins was supposed 

 to be supported by an incontrovertible argument de- 

 rived from the sulphuret of iron, which, it was asserted, 

 could not be formed from aqueous solution ; and the 

 same rule was therefore extended to all the other sul- 

 phurets. So far is this from being true, that Nature 

 does produce it from aqueous solutions, abundantly. 

 In art, it can be procured by the mere repose of the 

 Serum of blood, and from the decomposition of sul- 

 phat of iron by animal matters. Other metallic sul- 

 phurets may probably be formed in the same manner; 

 it is a subject that requires to be investigated by those 

 who may have leisure. These combinations can also 

 be procured in the aqueous method, by means of sul- 

 phuretted hydrogen ; a very probable agent in nature. 

 In these latter cases, the sulphurets are obtained only 

 in a powdery form, but in the former, the iron pyrites 

 is crystallized. 



Respecting the phosphurets, our direct experience 

 is little; and I need only remark, that the analogies 

 between sulphur and phosphorus are so strong, that 



