154 A TREATISE ON THE CONNECTION OF 



4p 



the proportion it may bear to the weight of the dry mould 

 pn which the experiment had been made. 



The same process and the same acid will serve to show 

 if magnesia be contained, and the proportion it may 

 bear to the soil. Magnesia is not in general found in any 

 very great proportion in surface mould, although there 

 is more of it contained in ground than is generally ima- 

 gined, It will, for the most part r be found accompanied 

 by calcareous matter ; and as both these substances, when 

 dissolved by the marine acid, are very soluble, and blend- 

 ed together, a separation is to be effected by the follow- 

 ing process.. 



The earths of magnesia and calcareous matter are to 

 be precipitated by mild mineral alkaline salt. The pre- 

 cipitate, or earthy residuum, when washed, is to be dis- 

 solved by a due proportion of the vitriolic acid diluted 

 with water. With the calcareous matter it will form 

 gypsum, (a very insoluble salt) whilst with the magnesia 

 it will form Epsom salt, a salt of great solubility. These 

 salts are to be separated by priority of chrystallization, 

 and their respective weights being ascertained, when 



deprived 



