COMPOSITION AND STRUCTURE OF METEORITES 



61 



THE INSOLUBLE SILICATE 



From the last treatment there remained slightly over 1 gram of 

 clean acid washed insoluble silicate. One-half gram (0.5000) of this 

 was weighed out, fused with sodium carbonate and analyzed by 

 standard methods to give the composition of the insoluble portion. 

 The chromite was undecomposed by the sodium carbonate fusion 

 and was weighed with the silica. It remained in the residue when 

 the silica was treated \\'ith hydrofluoric and sulphuric acids. After 

 weighing tliis residue was again treated in the platinum crucible 

 with hydrofluoric and sulphuric acids, evaporated to sulphuric acid 

 fumes, diluted with water and the chromite filtered out and weighed. 

 It was not in amount sufl&cient for analysis and, in the summation 

 below it is assumed to have the composition FeO.CroOs. The analy- 

 sis of the insoluble silicate gave the following results: 



Analysis of insoluble silicate portion 



Per cent 



SiOs 56. 94 



AI2O3 4.86 



TiOo Trace. 



FeO 8.98 



CaO 4.56 



MgO 22.28 



Per cent 



NiO None. 



Chromite 0.60 



NasO .87 



K2O 1.28 



100. 37 



No trace of nickel could be detected by the dimethylglyoxime 

 method. Alkalies were separatively determined by the J. Lawrence 

 Smith method and all assigned to the insoluble silicate. The direct 

 determination of alkalies in the remnant of the insoluble sUicate was 

 considered impractical, since the material had been digested in sodium 

 chloride and might have retained a minute amount of soda. This 

 remainder was therefore used for microscopic examination. 



The composition of the portion of the meteorite ground for analysis 

 is then: 



The unused acid and alkali extracted portion of the insoluble 

 silicate was screened free from fines and the portion between 80 and 

 200 mesh was passed through a methylene-iodide-bromoform heavy 

 solution in an attempt to isolate grains of feldspars for optical exam- 



