126 bichowsky: an unusual sulfur crystal 



This development of sillimanite by burning and its possible 

 abundance in porcelain'^ may be the explanation of another 

 feature noted. In some of the clays, as indicated in the de- 

 scriptions, a double refraction is produced in the ground mass 

 of the clay by burning to higher temperatures. It is very 

 probable that this is caused by particles too minute to be easily 

 recognizable, and that the development of the interference 

 color may be due to the formation of sillimanite. The single 

 and double refractions of the material would not be against it, 

 but it is not proven in any way except by analogy. 



In the sections where sillimanite was actually determined, it is 

 present in the form of slender crystals of fair size, and can surely 

 be distinguished b}' its moderate relief, low interference, optical 

 character, and cross fractures. 



In table 2 there are given in summarized form the features 

 which a number of the thin sections show. They are worth 

 recording, although the series is not sufficiently large to warrant 

 drawing definite conclusions. For further comparison the table 

 also gives the texture of the clay, relative abundance of the 

 important constituents, and porosity after burning. 



CRYSTALLOGRAPHY.— ^M. unusual stdfur crystal F. Rus- 

 sell Bichowsky, Geophysical Laboratory. (Communicated 

 by R. B. Sosman.) 

 The accidental mixing of a hot alcoholic solution of ammonium 

 polysulfide with a mixture of benzonitrile, hydroxylamine hydro- 

 chloride, and ether resulted, among other things, in the forma- 

 tion of the single, well-developed, orange-red, translucent crystal 

 figured below. The crystal was measured and figured (Fig. i) 

 under the impression that it was a crystal of some organic com- 

 pound, but later analysis showed that it was almost pure sulfur 

 containing 0.33 per cent carbon, 0.09 per cent hydrogen, o.io 

 per cent nitrogen, 0.07 per cent ash, and a trace of chlorine. 

 The density 2.01 is not unusual for sulfur, and the angles are 

 in close accord with those calculated, using the Goldschmidt^ 



^ Klein, A. A. The constitution and microstructure oi porcelain. Trans. Am. 

 Ceram. Soc. 18: 377. 1916. 



' GoLDSCHMiDT. Krystallographische Winkeltabellen, p. 313. Berlin, 1897. 



