226 W. G. Mixter—Heat of Combustion of Hydrogen. 



Weighting these means inversely as the squares of their prob- 

 able errors, we have for the mean of the three series 33993±16 

 calories for the heat of combustion of one gram of hydrogen at 

 constant pressure and formation of liquid water at 0°, and in 

 terms of the calorie at 20°. 



It may be stated that the aim has been to present an outline 

 of the work sufficient to show the character of it, omitting a 

 vast amount of detail. Every precaution was taken to ensure 

 accuracy and much time was spent in testing the thermometers 

 and in finding the most favorable room temperature for the 

 work. The investigation was the more laborious because a 

 room of fairly constant temperature was not available, and it 

 was often necessary to wait for hours or a day for the condi- 

 tions requisite for thermometric and barometric observations. 



Results of othek Inyestigators. 



In the following table the results of different investigators 

 are given in chronological order and for constant pressure. 

 Andrew's published result of 33808^ at constant volume is 

 increased 488^ for constant pressure. Likewise Than's observed 

 heat of 33822*^ at constant volume is 404^^ greater for constant 

 pressure. 



Calories. 



34473 DuloiJg. 

 34792 Hess. 

 34666 Grassi. 

 34246 Andrews."^ 



34462 ^^^^ =^"<^ , 



34178 Thomsen.:^ 

 o. ,.!/? JSchiiller and 



Wartha.§ 

 34226 Than. II 

 34495 Berthellot.l 



Temperature. 

 Heat of formation of 9 grams of water. 



combustion 1 



formation of 9 



'' 9 



98 



a u g.98 a 



" combustion of 1 '* 



hydrogen 20° -22° 



water 6°-12° 



" 16°— 20° 



hydrogen 9° — 10° 



Calculating the heat of combustion of one gram of hydrogen 

 from the heat of formation of the stated amounts of water on 

 the basis of the accepted ratios of 2*016 to 16 of hydrogen to 

 oxygen in water, we have 



*Phil. Mag. [3], xxxii, 321, 1848. 

 t Ann. Chem. et Phys. [3], xxxiv, 349, 1853, 

 X Thermochemischen Untersuchungen, ii, 52. 

 §Ann. Phys. u. Chem. N. F., ii, 371, 1877. 

 II Ann. Phys. u. Chem. N. F., xiv, 393, 1881. 

 ^ Ann. Chem. et Phys. [6], xxx, 553, 1893. 



