abstracts: mineralogy 151 



PHYSICS. — Note on the calibration of optical pyrometers. Paul D. 

 FooTE. Metallurgical and Chemical Engineering, 11: 97. 1913. 

 This note is a suggestion of a method for the calibration or checking 

 of optical p3Tometers. The only new feature is the construction of the 

 "black body" uj^on which the pyrometers are sighted. A small enclo- 

 sure, turned on the end of a graphite conical tube, dips into a graphite 

 crucible containing 1000 to 1500 grams of molten metal, the pot being 

 heated within an electric resistance furnace. Melting and freezing 

 curves show the proper value to assign to the pyrometer reading, the 

 flat part of the curves corresponding to the temperature of melting 

 or of freezing. P. D. F. 



MINERALOGY.^ — A study of the tourmaline group. Waldemar T. 



ScHALLER. Zeits. f. Krystallographie und Mineralogie, 51: 321- 



343. 1912. 

 Analyses of tourmalines from Elba and California are given as well 

 as their crystallographic constants, densities and refractive indices. 

 The correlation of the physical and chemical properties is imdertaken 

 and by using also the available published data, the following conclusions 

 are reached: (1) The general formula proposed by Penfield and Foote, 

 namely H2oB2Si402i, is confirmed. (2) Some analyses do not give 

 enough water to yield the ratio 12 Si02.4H20 but only 12 Si02.3H20. 

 (3) The phenomenon of solid solution (as distinct from isomorphous 

 mixture) does not play any role in tourmahne. (4) The percentages of 

 AI2O3 and RO vary reciprocally in direct proportion. (.5) The mineral 

 tourmaline can not be represented by two, three or four definite formu- 

 las. General formulas can be deduced but at least four are required. 

 The number of definite formulas or components, as they may be called, 

 is large, not less than eight and probably more. (6) The crystallographic 

 and physical properties vary in relation to the changes in chemical com- 

 position but the trustworthy data available are too meager for an exact 

 correlation. Nevertheless all the determined changes are always in 

 the same direction and approximately of the same order of magnitude, 

 as shown by the diagrams in the original paper. Those tourmalines 

 containing about 35 to 36 per cent xlloOs show the maximum specific 

 gravity, refractive indices and double refraction and the longest c-axis. 



W. T. S. 



