232 W. G. Mixter—Heat of Oxidation of Tin. 



4656 c for one gram of oxygen taken up or 74500 c for sixteen 

 grams. The result was thought to be high and therefore 

 another lot of stannous chloride was prepared as follows : 

 about 400 grams of pure stannous chloride were dissolved in 

 four liters of hot water and a solution of pure sodium hydroxide 

 was added in sufficient quanity to dissolve part of the stannous 

 hydroxide formed. The mixture was kept hot until most of 

 the white particles had disappeared. The product was washed 

 by decantation in order to remove the smaller particles present. 

 The stannous oxide was in the form of minute dark crystals. 

 It was free from chlorine and sodium; dried at 100° it con- 

 tained 0*41 per cent of water, which was determined as follows : 

 a weighed portion was burned in dry oxygen in order to attain 

 a high temperature and the water was absorbed in a chloride 

 of calcium tube. The determination of stannous oxide was 

 made thus : 1*1193 grams of substance were heated in air and 

 oxygen. The stannic oxide formed weighed 1*2425 grams and 

 the observed gain in weight was 0*123 gram. Adding to this 

 last number 0*0046 gram of water present before burning 

 we have 0*1276 gram of oxygen taken up, which is equivalent 

 to 96*2 per cent of SnO. 



For the calorimetric work the stannous oxide, dried at 100°, 

 was placed on a silver foil tray which was supported at the top 

 of the lower silver cup or lining of a 500 cc bomb and then the 

 cup and contents were counterpoised on a balance. After a com- 

 bustion the cup and contents were heated to expel moisture, 

 allowed to cool and then the increase in weight noted. At the 

 time of a combustion the tray melted and the oxide fell to the 

 bottom of the cup, where it was found in the form of a porous 

 white crystalline cake. The experiments were as follows : 



8 9 10 



Substance taken 30*06 30*89 30*58 grams 



Amount + 0*962 = SnO__. 28*92 29*72 29*49 

 SnO equivalent to oxygen 



consumed 28'74 29*74 29*4 



Increase in weight 3*340 3*455 3*415 



Water in substance taken _ 0*123 0-126 0*125 



Fe o 0, from iron —0*056 —0*056 —0*056 



Oxygen consumed 3*407 3*525 3*484 



Water equivalent of system 3422* 3430* 3476* 



Temperature interval 4*422° 4-541° 4*469 



Heat observed .. _ __. 15133 c 15576 c 15534 c 



" of oxidation of iron.. — 64 c — 64 c — 64 c 



15069 c 15512 c 15470 c 



