550 T. S. HUNT'S ANALYSES. 



there is also present a portion of silicate of iron and magnesia, decomposable by acids. In 

 my analysis the powdered magnesite was digested for a long time at a boiling heat, with hy- 

 drochlorite acid ; the insoluble portion was then boiled with strong sulphuric acid, and from 

 the residue the silica was removed by a solution of carbonate of soda, the talc remaining. 

 " The talc thus purified from magnesite and serpentine by successive treatments with 

 hydrochloric and sulphuric acid and carbonate of soda, was gently ignited, and then de- 

 composed by fusion with carbonate of soda ; it gave : 



Silica, 62.60 



Magnesia, ...... 31.30 



Allumina and oxyd of iron, . . 4.06 



Water and loss, 2.04 



100.00 



In the analysis of Dr. Hayes just cited [I.], the 48.80 parts of carbonic acid are suffi- 

 cient only for 44.36 parts of magnesia, leaving 1.24 of this base in the form of a silicate 

 decomposable by sulphuric acid. In order to determine the composition of this silicate, 

 a dark-green portion of the rock was pulverized, and boiled for a long time with dilute 

 nitric acid, which dissolved a large amount of magnesia with disengagement of carbonic 

 acid ; the solution contained besides, magnesia, iron, manganese and a trace of nickel, but 

 no lime. The undissolved residue was then boiled with a solution of carbonate of soda, 

 which took up a considerable amount of silica derived from the silicate which had been 

 partially decomposed by the nitric acid, and left a dense granular matter mingled with 

 silvery scales of greenish talc, which were in great part removed by washing. The denser 

 silicate was then dried at 250 F., and submitted to analysis. By ignition it lost 11.40 per 

 cent, and then gave to a boiling solution of nitrate of ammonia a quantity of magnesia 

 equal to 1.21 of carbonate. Another portion was decomposed by sulphuric acid, and the 

 silica separated from the insoluble talc by a solution of carbonate of soda. The results of 

 the analysis were as follows : 



Silica, 39.60 



Magnesia, 36.72 



Protoxyd of iron, .... 4.86 



Oxyd of nickel, traces 



Talc, 6.80 



Water, . , 10.77 



Carbonic acid, 0.63 



99.38 



" Deducting the talc, the carbonic acid, and the amount of magnesia required to form 

 with it 1.21 of carbonate, we have for the composition of this silica dried at 250 F : 



Silica, 43.34 



Magnesia, 39.55 



Protoxyd of iron, .... 5.32 



Oxyd of nickel, ..... traces 



Water 11.79 



100.00 



