Mixter — Formation of Trisodium Orthophosphate, etc. 103 



Art. XII. — The Heat of Formation of Trisodium Ortho 

 phosphate, Trisodium Orthoar senate, the Oxides of Anti- 

 mony, Bismuth Trioxide / and fourth paper on the Heat 

 of Combination of Acidic Oxides with Sodium Oxide / by 

 W. G. Mixter. 



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



The heat of combination of an acidic oxide with sodium 

 oxide may be derived from the heat of formation of the anhy- 

 drous salt, and, conversely, the thermal effect of the union of 

 the elements in a salt may be calculated from the heat of com- 

 bination of the oxides forming it. Only the latter method is 

 applicable to insoluble salts of weak acids, as, for example, 

 sodium antimonate. The investigation includes new determi- 

 nations of some constants and the results obtained agree with 

 those of other investigators and show the value of the sodium- 

 peroxide method. 



Kilogram-calories, which are indicated by the decimal point, 

 are used in some of the calculations for sake of brevity. The 

 gram-calorie is, however, more philosophical, as the gram is 

 the unit of mass in physical science and quantities in chemis- 

 try are commonly expressed in grams. Unless otherwise indi- 

 cated, the constants used in the calculations are Thomsen's and 

 are taken from his Thermochemistry, the English translation 

 by Katharine A. Burk. 



THs o dium Orthoph osph a te. 



The red phosphorus for the work was digested, with hot 

 dilute nitric acid, next with a concentrated solution of sodium 

 hydroxide and then washed and dried. When exposed to 

 moist air for twenty-four hours, it gained in weight 0*16 per 

 cent. The following are the experimental data : 



1 2 



Phosphorus. 1 -000 gram 1*000 gram 



Sodium peroxide 12 " 13 " 



Water equivalent of system 4,136 " 3,999 " 



Temperature interval-. -.. 1*986° 2*004° 



Heat observed __. 8,214 c 8,014 c 



" of oxidation of iron _ — 48 c — 48 c 



For 1 gram of phosphorus 8,166 c 7,966 c 



In the first experiment the mixture was in a silver cup the 

 rim of which only was in contact with the cold sides of the 

 bomb. With this arrangement the fusion cools slowly and 



