230 IF. G. Mixter—Reat of Oxidation of Tin. 



derived from the weight of tin taken, of oxides formed, and 

 of ferrous-ferric oxide from the iron used for ignition. The 

 experimental data are as follows : 



1 2 



Tin 8*121 grams 11 -070 grams 



" equivalent to oxygen com- 

 bined _ 7-122 " 9-364 " 



Oxygen combined 1*910 " 2*518 " 



Water equivalent of system 3631* " 3482* " 



Temperature interval .. _ 2*366° 3*239° 



Heat observed 8591° 11279° 



" of oxidation of iron —80° — 80 c 



S511 c 11191° 



For 1 gram of oxygen 4456 c 4444 c 



The combustions were evidently incomplete as indicated by 

 the figures and by the fact that there was formed a considerable 

 amount of a black substance along with the white stannic 

 oxide. The results are 4 per cent higher than those obtained 

 with tin foil in experiments 3 and 4. It might be surmised 

 that tin separated from a sodium-tin alloy is an allotropic 

 form and it may be when the separation is made at a low 

 temperature, but the powder which had been heated to 100° 

 is the ordinary modification, for, as shown later, it gives the 

 same heat when burned with sodium peroxide as ordinary 

 crystalline tin. The high result is evidently due to the forma- 

 tion of a considerable amount of stannous oxide. But the 

 heat effect of Sn-f-0 is less than that of SnO + O, and hence it 

 appears probable that the two oxides formed in the com- 

 bustion had combined with evolutions of heat. Moreover, 

 the sesquioxide of tin is known and is dark colored. 



The next experiments were made with tin foil, which a 

 qualitative analysis showed to be quite pure. It was also 

 tested as follows : 2*911 grams were treated with nitric acid, 

 the latter removed by evaporation, the residue digested with 

 dilute nitric acid and washed on a filter and finally heated 

 over a blast lamp until the weight was constant. The stannic 

 oxide obtained weighed 3*700 grams, equivalent to 2 916 

 grains of tin. (Sn=119.) For the combustions the foil was 

 placed in loose rolls in the bomb, which was then filled with 

 dry oxygen at a pressure of 12 atmospheres. The conditions 

 were the same as in experiments 1 and 2 except that the foil 

 exposed a larger surface to the oxygen. The stannic oxide 

 resulting was in the form of a porous cake which was brown- 

 ish on the surface but white in the interior. The entire cake 



