, Mixter — Combustion of Silicon and Silicon Carbide. 135 



The agreement of the calculated with the experimental result 

 indicates, in the reaction between carbon and an excess of 

 sodium peroxide, that sodium metacarbonate is formed and not 

 the orthocarbonate. The latter is not known, but if it may 

 result by the union of the metacarbonate and sodium oxide the 

 thermal effect would be about the same as that of the oxidation 

 of sodium oxide. 



Combustions in Oxygen. 



The combustions were made as follows : A mixture of acety- 

 lene carbon and silicon carbide or silicon was placed in a 

 shallow silver foil dish supported near the middle of the bomb. 

 The object was to expose a large surface of the mixture when 

 burning to oxygen. Naphthalene and anthracene were tried 

 but did not answer as well as finally divided carbon. That the 

 temperature was sufficient to volatilize silicon was shown by 

 the deposition of silica on the sides of the bomb in the form of 

 a white powder. It settled very slowly in water and passed 

 through filter paper. Under the microscope it was found 

 to be spheroidal and non-crystalline. The silica from burn- 

 ing silicon carbide was all in a finely divided form, while 

 in that from silicon globules 2 or 3 mra in diameter were 

 found. The residue left by the combustion was treated 

 with nitric acid to dissolve silver present and, after thorough 

 washing, was repeatedly digested with hydrofluoric acid 

 until its weight when dry was constant. Finally the residue 

 was treated with nitrohydrofluoric acid, the loss being silicon 

 and the powder remaining silicon carbide. The thick platinum 

 electrodes, placed 4 or 5 cm3 above the combustible mixture in 

 the bomb, were more or less melted by the combustions. In 

 one instance a globule of platinum silicide formed which was 

 found to contain 7 per cent of silicon. In no instance was 

 silicon found in the platinum melted by the burning of silicon 

 carbide. 



Experiment 7. 



Silicon carbide . 



" " in residue 



Silicon " " 



Silicon carbide burned 



Iron for ignition 



Oxygen 



Water and water equivalent of system • 3433 



0-9820 



grams. 



0-1700 



u 



0-0068 



(C 



0-8052 



£< 



0-0466 



a 



11 



(C 



