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



one liter of air is 1*293 gram in latitude 45° and in New Haven 

 it is 1'2926 gram. No correction was made for the small ele- 

 vation of the laboratory above the sea level. The coefficient 

 of expansion of both hydrogen and air used in the calculations 

 is 0-00866. 



The apparatus employed in tilling the bomb with hydrogen is 

 shown in tig. 2, page 217. The generator K was charged with 250 

 grams of sheet aluminium and a solution of sodium hydroxide 

 of density 1*1. Owing to the alkali held by the bulky sedi- 

 ment which formed on the metal the gas was evolved for 

 hours and often for days after the stop cock was closed, thus 

 expelling the air from K and L. The latter vessel contained 

 water to keep air from contact with the solution in K. Each 

 series of experiments was made with one charging of the gene- 

 rator. For the last series zinc was substituted for aluminium. 

 The hydrogen was tested for arsenic by the Marsh method, 

 though if present none was likely to escape the alkali ; for 

 carbon compounds by passing it over glowing copper oxide and 

 then into lime water ; and for ammonia by the Nessler test. 

 None of these impurities was detected. The jar P contained 

 2|^ kilos of potassium hydroxide, in sticks. Hydrogen or air 

 after passing through this drying jar yielded to phosphorus 

 pentoxide only 0*2 milligram of water per liter, an amount 

 too small to affect the results. The method is well suited to 

 drying rapidly large volum.es of gas. The manometer M is a 

 barometer and tube as shown. The apparatus was exhausted 

 by means of large water-aspirator pump connected at B. To 

 prevent moisture or air passing into the apparatus mercury was 

 placed in S so that the end of T dipped into it. The bottle A 

 with its tubes is for removing the mercury from S when neces- 

 sary. The small brass tubing of the connections was tinned 

 and varnished. The bomb was protected from changes of 

 temperature by a glass jar packed in cotton wool in a wooden 

 box, which stood in the hood with the balance. 



The relative mass of the bomb was obtained as follows : It 

 was repeatedly filled with air dried by potassium hydroxide 

 and finally closed after noting the temperature and pressure. 

 It was then counterpoised on the balance by a silver plated 

 copper bomb of like shape and size. Next the air was exhausted 

 to 15 or 20'"°' pressure and the loss in weight noted. The 

 bomb was next tilled with hydrogen at a known temperature 

 and low pressure and weighed again. The relative mass of the 

 bomb in the first case is the mass of the counterpoise less the 

 calculated mass of contained air. In the second and third 

 instances it is less the weight required to counterpoise it again 

 plus the calculated weights of the contained gases. The mean 

 of the three results was taken as the mass of the bomb. 



