Mixter — Combustion of Silicon and Silicon Carbide. 131 



grams losing only 0'5 gram. It was finally digested with only 

 hydrofluoric acid, but there was no further loss in weight. The 

 purity of the product was found as follows : 0-5251 gram was 

 fused in a platinum crucible with 5 grams of potassium nitrate 

 and 10 of sodium carbonate, and the silica was separated with 

 the usual precautions. Silicon found 69'9, calculated 70*3 per 

 cent for SiC ; Si =284. 



Combustions with Sodium Peroxide. 

 ' The bomb used in all of the work was one described in the 

 paper on carbon.* It was lined with silver cups l mm in thick- 

 ness. Owing to the danger of melting the lower cup the com- 

 bustible mixture was usually placed in a thick silver dish 

 resting near but not in contact with the bottom of the bomb. 

 This dish was usually melted by the combustion. Silver, as is 

 well known, is oxidized by molten sodium peroxide, but the 

 amount of oxide formed is small and the error caused is slight. 

 A nickel dish was tried, but this was attacked much more than 

 the silver one. After a combustion with sodium peroxide the 

 fused mass resulting was dissolved in a large quantity of water 

 and the insoluble unburned substance was collected, purified 

 and its weight deducted from the amount of material used for 

 the experiment. In case of silicon some may have dissolved 

 in the dilute alkaline solution, but this was not likely, as silicon 

 is taken up slowly by concentrated alkali. In order that the 

 iron used for ignition should burn well the bomb was filled 

 with oxygen at atmospheric pressure. The carbon used was 

 the acetylene modification described by the writer.f 



Experiment 1. 



Carbon ] -0530 grams. 



" not burned _o-0143 " 



" burned 1-0387 " 



Iron for ignition 0072 " 



Sodium peroxide . 19 " 



Water 2954 " 



" equivalent of calorimeter 311 " 



" sodium peroxide and carbon 4 " 



" " "system 3269 " 



Minutes. Temperature. Temperature interval. 



18-452 22-012 — 18-458 + 0-009 = 3-563° 



1 18-454 



2 18-458 Heat observed 3269X3-563 = 11648° 



3 22-012 " of oxidation of iron — 115 c 

 9 22-012 



10 22-009 11533 c 



11 22006 



12 22-003 For 1 gram of carbon 11103 c 

 * This Journal, xix, 435. f Loc. cit. 



