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



Art. XX. — On the Heat of Combustion of Hydrogen ; by 



W. G. MlXTER. 



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



The constant for the heat of combustion of hydrogen is 

 fundamental in thermal chemistry and its values found in the 

 more recent investigations differ by nearly two per cent. 

 While the results of Thomsen, Schuller and Wartha, and Than, 

 agreeing closely, may be regarded as quite accurate, it appeared 

 desirable to obtain additional data, and also to make a critical 

 investigation of the bomb method of calorimetry now in gen- 

 eral use. Andrews made good determinations of the heats of 

 combustion of hydrogen and carbonic oxide with a copper 

 bomb in 1 848 but his method does not appear to have been 

 used again until Berthellot perfected it. 



The calorimeter, lig. 1, consists of the bomb B, the calori- 

 meter vessel C, supported by the wooden ring W in the tin 

 vessel A which is surrounded by the double-walled copper 

 tank containing 20 liters of water. The water in the calori- 

 meter is stirred by two small propellers. The bomb is fine 

 silver except the stem of sterling silver. Its capacity was 

 found by filling it with boiling water, allowing to cool, best in 

 a tank of water in a room of constant temperature, and weigh- 

 ing with the usual precautions. Determinations were made at 

 4° and common temperature and the difference in volume 

 observed accorded well with that calculated with the coefficient 

 of expansion of silver. The internal volume of the bomb was 

 found to diminish O'lS^'^ when the internal pressure was made 

 737™''' less than the external, and to recover its original volume 

 when the internal pressure was restored. No correction was 

 made for this change in volume in the exhausted bomb. After 

 several explosions the capacity of the bomb was found to have 

 increased 0-2h'"^ by each explosion. An internal pressure of 16 

 atmospheres for 18 hours expanded it 0-3^'' and the internal 

 volume was then 1110-56''° at 18°. After lying unused eight 

 months it was found to be 1110*58'=^ The capacity of the 

 stem of the bomb is O'S'^^ E is an insulated platinum electrode 

 for sparking the gas. The calorimeter vessel C is german sil- 

 ver and is nickel plated on the outside. The water equivalent 

 of it and the bomb was derived from the specific heats given 

 in Landolt and Bernstein's Physikalish-Chemische Tabellen, 

 using Naccari's numbers for copper at 17°, zinc at 18°, silver 

 at 23°, and Regnault's for nickel between 14° and 97°. 



