Penfield and Foote — Composition of Tourmaline. 117 



As indicated by the variations in the ratios, the analysts 

 apparently have not had sufficient experience to enable them 

 to deal successfully with such a difficult problem as the tourma- 

 line analysis. The average of the ratios, however, approximates 

 to 4 : 1 : 20 and thus substantiates our formula. 



Titanium in touemaline. — Titanium seems to have been 

 overlooked in the earlier analyses of tourmaline, but is reported 

 in several of the analyses of Riggs, Jannasch and Kalb, and 

 others. The quantity, however, has always been found to be 

 small, amounting to over one per cent (reckoned as Ti0 2 ) in 

 only four of the analyses and to over 0*6 per cent in but two 

 others. It has not been taken into consideration in making 

 the foregoing calculations, partly because it would exert no 

 appreciable influence on the final result, but chiefly because it 

 is uncertain whether the titanium in this mineral plays the 

 part of a tetravalent element replacing silicon, or of a triva- 

 lent element replacing aluminium. Although it may not 

 be possible with the data now at hand to definitely settle 

 this question, still the analyses furnish some evidence that 

 the element should be regarded as trivalent. This result 

 has been reached by considering titanium both as Ti0 2 replac- 

 ing SiQ 2 and as Ti 2 3 replacing A1 2 3 , and comparing the ratios 

 derived from the four analyses in which the Ti0 2 has been 

 recorded as over one per cent. The results are as follows : 



No. 



51 



Locality. 



Monroe, Conn., 

 Riggs 



53. Gouverneur, N. Y., 

 Riggs 



56. Snarum, 



Jannasch and Kalb 



59. Tamatawe, 



Jannasch and Kalb 



Premises. Si0 2 

 Tl0 2 , 1-61 per cent.. .4 

 Neglecting titanium.. 4 

 Ti 2 3 T45 per cent. ..4 

 Ti0 2 1-19 per cent ...4 

 Neglecting titanium. .4 

 Ti 2 3 1-07 per cent.. .4 

 Ti0 2 1-10 per cent. _ .4 

 Neglecting titanium . _ 4 

 Ti 2 G 3 0*99 per cent. ..4 

 Ti0 2 1-22 per cent... 4 

 Neglecting titanium -_4 

 Ti 2 3 1-10 per cent 4 





Total 



B 2 3 hydrogen. 



0*88 



: 18*9 



0-91 



: 19-6 



0*91 



: 19'97 



0-95 



: 18-5 



0-97 



: 18-9 



0-97 



: 19.2 



0-93 



: i9-i 



0-96 



: 19-7 



0-96 



: 19-9 



0-90 



18-4 



0-92 



; 18-8 



0-92 



: 19-1 



In these four cases it will be observed that the calculations 

 give the closest approximation to the normal tourmaline ratio 

 when the titanium is regarded as Ti 2 3 . Moreover when the 

 titanium is regarded as Ti0 2 the departure from the normal 

 ratio is so great that it does not seem probable that this is due 

 wholly to defects in the analyses. Some very careful and 

 exact analytical work must be done in order to decide this 

 ^question definitely. 



