104 Penfield and Foote — Composition of Tourmaline. 



Si Si 



/A\ //\\ 



ooo o oooo 



I I I \ / I I I 



RRR Al RRR 



I 

 O 



I 



or [Si0 4 ] 2 [A10 . BO]([A10] 2 , Mg, Fe, Na„ Li 2 , H 2 ) 3 



That the univalent radical [AlO] can replace R' does not 

 appear in the original article of Jannasch, and it makes a 

 decided difference whether three R's are replaced by one atom 

 of Al or by three [AlO] radicals. The latter assumption 

 implies a "basic character which tourmaline does not possess. 



We have thus reviewed the work already done in order to 

 show the difficulties which this problem has presented. It is, 

 however, interesting to note how closely different investigators 

 come to one type of acid from which all varieties of tourma- 

 line are derived. For the sake of comparison these acids have 

 been reduced to four silicon atoms, and are given below, both 

 as borosilicic acids and with the boron replaced by hydrogen. 



Rammelsberg 



f H, 8 B 2 Si 4 0„ 

 1 H.^B^SiA. 



or 

 or 



H M Si.O,.=H.SiO. 

 H 2( Si 4 M 





fH, 8 B,Si 4 2 . 



or 



H 21 Si ( M 



Riggs 



1 H,ASi ( O !0 

 1 H^Si.O,, 



or 

 or 



H a ,Si 4 (Irrational) 





LH 1 „ 88 B s Si,0 2 „, 6 



or 



H m. Sl . .... 



Jannasch and Kalb 



1 H,,B,8i t O,. 

 1 Ji,A8i.O„ 



or 



or 



H 21 Si,0 41 



H„Si,0„ 



Willfing 



H s „B a Si«O SI 



or 



H 5 ,Si,0 21 



Goldschmidt 







H s , 8 Si 4 O s „., 



Rheineck 



1 H,„B 1 . i 8i.O,... 



or 

 or 



H „.,S>A... (Irrational) 

 H 24 .,Si_ 1 2 , s etc. 



Clarke 



H 19 . as B ! Si 1 !G . 66 



or 



H„.„Si,0,,,. M 





New Analyses.. 





Method of analysis. — The present investigation was under- 

 taken with the expectation that for the solution of the problem 

 in hand it would probably not be necessary to make a long 

 series of analyses but rather exceedingly accurate analyses of a 

 few carefully selected types of tourmaline. We therefore 

 prefaced our work by a careful study of those features of the 

 tourmaline analysis, which have proved most difficult. The 

 method proposed by Gooch* of distilling off the boron with 

 methyl alcohol and weighing it as calcium borate is very exact, 

 * Amer. Chem. Jour., ix, p. 23. 



