L32 II. G. Mixter — Thermochemistry of Silicon. 



Evidently the values for hydrofluosilioic acid and silicon tetra- 

 chloride are subject to the uncertainty in the value for silicon 

 tetrachloride from which the value for silicic acid is derived 



and also to the nnestahlislicd heat effect of 8i(crys.) > 



Si(anior.V Nevertheless the writer's results indicate that the 

 thermochemistry of silicon, excepting the tetrachloride and 

 silicic acid, is fairly well established. 



Table II, under II, I And J, contain experiments with silica 

 holding 1*8 per cent of combined water and considerable 

 adsorbed water. The results indicate that more energy is 

 required to separate adsorbed water and convert it into the 

 liquid state than to melt ice. This is what would be expected. 

 The molecular condition of adsorbed water has not been found. 

 Such water is known to have a lower freezing point than 

 ordinary water and Foote & Saxon* have shown that it is 

 different from combined water. 



Art. XV". — Composition of the Selensulphur from Hawaii ; 

 by Glknn Y. Brown. 



In the course of an investigation of the chemical reactions 

 of selenium, the writer had occasion to look' up the occurrence 

 of this element in nature. It is usually found combined in 

 selenides of the heavy metals, but also occurs free, especially 

 in volcanic regions. One of its most frequent forms is as an 

 isomorphons mixture with sulphur, named selensulphur in the 

 books on mineralogy. Selensulphur is classed by Danaf as a 

 mineral species, No. 4, and is described as " an orange-red or 

 reddish brownish mineral containing sulphur and selenium, but 

 in unknown proportions." It seemed incredible that no quan- 

 titative analysis had ever been made of a mineral known since 

 1825 and reported to occur at a number of localities, yet such 

 appears to be the case, for no analysis could be found in any 

 available book on mineralogy or chemistry. On talking over 

 the matter with Dr. Edgar T. Wherry, Assistant Curator, 

 Division of Mineralogy and Petrology, United States National 

 Museum, the writer learned that at least one authentic speci- 

 men of selensulphur was included in their collection, and 

 through the kindness of Richard Rathbun, Assistant Secretary 

 in charge of the Museum, a small fragment of this specimen 

 was received for investigation. This specimen was collected 



* Jour. Am. Chem. Soc, xxxviii, 588, 1916. 



f System of Mineralogy, 6th edition, 1892, p. 10. 



