Minerals of the Composition MgSiO^ 



389 



well developed for gouiometric measurement. The best 

 results were obtained by following the conditions just referred 

 to for the formation of wollastonite.* 



With Magnesium Chloride in a stream of Hydrochloric 

 Acid Gas. — These experiments were carried out in the plat- 

 inum crucible fig. 1, invented by Professor G-ooch for the 

 determination of water in difficultly decomposable silicates. f 

 It consists essentially of a long crucible slightly conical in 

 form, with a collar around the top so constructed as to leave a 

 narrow groove between it and the cap which covers the cruci- 

 ble. Into this groove sodium tungstate can be melted to form an 

 air-tight seal. The cap is so constructed as to permit the pas- 

 sage of a current of gas through the crucible. 



Two or three grams of magnesium silicate were first put 

 into the dry uncovered crucible. A quantity of anhydrous 

 magnesium chloride, prepared by the decomposition of mag- 

 nesium-ammonium chloride;};, was heated just before the experi- 

 ment in a current of dry hydrochloric acid gas, cooled and 

 dropped immediately into the crucible. The cover was then 



*Loc. cit. 



fBull. U. S. Geol. Survey, No. 176, p. 42. 



X It is not easy to prepare magnesium chloride in quantity free from oxide ; 

 the product of the decomposition of magnesium-ammonium chloride, as this 

 is ordinarily carried out, requires a thorough treatment with dry hydro- 

 chloric acid gas. 



