PHYSICAL AND LITERARY. 167 



joining itfelf to the earth by a ftronger attra- 

 ction 5 and upon this account the magnefia of, 

 fea-water feems to be different from either of 

 thofe defcribed by Hoffman. He fays ex- 

 prefsly, that the folutions of each of his pow- 

 ders, or, what is equivalent, that the hquors 

 from which they are obtained, formed-^ 

 coagulum, and depofited a white powder, 

 when he added the vitriolic acid*j which 

 experiment I have often tried with the 

 marine bittern, but without fuccefs. The; 

 coagulum thus formed in the mother- of 

 nitre may be owing to a quantity of quick-^ 

 lime contained in it j foir quick-lime is ufed 

 in extrading the falt-petre from its matrij^ 

 But it is more difficult to account for the^dif-^ 

 ference between Hoffmann bittern and QUfsi,j 

 unlefs we will be fatisfied to refer it t9 this^ 

 that he got his from the waters of fait fprings, 

 which may pofTibly be different from thofe 

 of the fea. .•!- . 



, Magnesia is not lefs remarkably diflrn- 

 guifhed from the calcarious earths, by joining 

 it to the nitrous and vegetable acids, than to 

 the vitriolic. Thofe earths, when combined 

 with fpirit of nitre, cannot be reduced to a 



cryftalline 



* HofF. Op. T. iv. p. 480 & 500. 



