W. G. llixter — Heat of Oxidation of Tin. 229 



Art. XV. — The Heat of Oxidation of Tin, and second paper 

 on the Heat of Combination of Acidic Oxides with Sodium 

 Oxides j by W. G. Mixter. 



[Contributions from the Sheffield Chemical Laboratory of Yale University.] 



Tin. 



The heat of oxidation of tin obtained by different investi- 

 gators varies widely and the work was done before calorimetry 

 was perfected by Tkomsen, Berthelot, and others. Moreover, 

 the constants of oxidations are required in calculating the heat 

 of formation of sodium stannate ; hence it seemed desirable 

 to make new determinations. Depretz* found for the heat of 

 oxidation of the stannic oxide 170000°. Dulong,f in 1838, 

 determined the heat evolved by the union of one liter of oxygen 

 with tin and obtained 6411 c , 6325 c and 6790 c ; mean 6509 c , 

 or for 32 grams of oxygen 145600°. Andrews,;}; who first 

 invented a calorimetric bomb, made in 1848 good determina- 

 tions. He mixed tin with broken quartz in a copper bomb, 

 ignited the metal with a milligram of phosphorus and found 

 the gain in weight. His results for one gram of oxvgen were 

 4235°, 4244 c and 4210 c .; mean 4230 c , or for 32 grams of oxygen 

 135360 c at constant volume and 136000° at constant pressure. 

 Likewise for the combustion of stannous oxide he obtained 

 4353 c , 4328 c and 4364 c ; mean 4349°, or for 16 grams of oxygen 

 695S4 C at constant volume and 69900 c at constant pressure. 

 The writer has used essentially Andrews' method. 



Experiments were first made with tin from a sodium alloy. 

 Dr. C. H. Mathewson, to whom the writer is indebted for 

 much good material for use in investigations, made a consider- 

 able quantity of an alloy having approximately the composition 

 Xa 2 Sn. This was pulverized and dropped into absolute 

 alcohol. After the reaction had moderated, water was added 

 gradually and then the metal was subjected to boiling water 

 for several hours and washed thoroughly. The powder was 

 grey and when magnified appeared to be made up of minute 

 leaves. The stannic oxide from 1-616 grams of the metal 

 weighed 2*060 grams, equivalent to 1'623 of tin. It was found 

 to contain 0*12 per cent of sodium. This amount of impurity 

 affects the heat result but slightly. For the calorimetric 

 experiments the tin powder was placed in a weighed silver 

 foil tray which was supported in the middle of a 500 cc bomb 

 in order that, as the tray melted, the hot powder would fall 

 through the oxygen. The weight of oxygen taken up was 



*Landoldt-Bornstein, Physicalisch-Chemische Tabellen, refer to Ann. Ch. 

 Phys., xxxvii, 180. This reference the writer has not been able to find. 

 + C. R., rii, 871. {Phil. Mag. (3), xxxii, 321. 



Am. Jour. Sci. — Fourth Series, Yol. XXYII, No. 159. — March, 1909. 

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