DR T. THOMSON on Asbestus, Chlorite, and Tak. 375 

 lysis, the constituents were found to be, 



y .A ' \ " O 



Silica, "... . . . 62.588 



Magnesia, . .,-*-. - 30.328 



Protoxide of iron, . . 3.848 



Water, V . , . . 3.400 



100.364 



. 



This is equivalent to, 



5.21 atoms silica, 

 2 atoms magnesia, 

 0.14 atoms protoxide of iron, 

 0.5 atoms water. 



c - * * ' - 1 - 



If we allow for the presence of a small quantity of bisilicate of 

 iron (probably accidental), talc may be considered as composed 

 of 



5 atoms silica, 

 2 atoms magnesia. 



. * t . - 



It is, therefore, a compound of, 



1 atom bisilicate of magnesia, 

 1 atom tersilicate of magnesia. 



Thus its chemical constitution differs from that of every other 

 mineral hitherto examined. Venetian talc, then, is entitled to 

 rank as a distinct mineral species. 



i .;U; ,; t. . .-.,-' 



