436 W. G. Mixter — Carbon and its Heat of Combustion. 



A cylindrical glass vessel with a long neck and stopcock and 

 having a capacity of 67 cc was filled with 3 grams of acetylene 

 carbon. It was exhausted and heated for an hour to about 

 400° and then allowed to cool and the stopcock closed, the 

 mercury pump being in action all the time. Next it was 

 counterpoised by a similar vessel and the needed weights, and 

 finally dry air was admitted and the increase in weight observed. 

 The data required are the weight and density of the carbon, 

 the capacity of the vessel, the weight of the air admitted, the 

 temperature and barometric pressure. The results of three 

 determinations were 3*2, 3*4, and 3*1 milligrams of air con- 

 densed by 3 grams of the carbon. The apparatus was crude 

 and the result is to be regarded merely as proving that but 

 little air is condensed by the carbon. 



The carbon for the first series of tests was from the sample 

 obtained three years ago in the determination of the heat of 

 dissociation of acetylene.* It contained a little incombustible 

 matter or ash derived from the bomb and the impurities of the 

 gas from which it was made. The composition of it was 

 found as follows : The carbon was compressed in a large plati- 

 num tray open at one end and nearly closed on top and the 

 tray and contents were placed in a long narrow platinum cruci- 

 ble with a close-fitting cover and heated to redness. After 

 cooling over sulphuric acid the whole' was weighed, then 

 heated again, allowed to cool as before and then the weight 

 was quickly taken, With these precautions the error due to 

 moisture is negligible. The observed weight was corrected 

 for ash, absorbed air and reduced to weight in vacuum. The 

 combustion was made with oxygen and oxide of copper. The 

 water was absorbed in a U-tube filled with beads drenched 

 with sulphuric acid and the carbon dioxide by a solution of 

 potassium hydroxide in a helical tube, the unabsorbed gas 

 passing through a U-tube filled with solid potassium hydroxide 

 and then through another tube containing beads drenched with 

 sulphuric acid. To the last tube there was an attachment to 

 keep out moisture. Each piece of absorption apparatus was 

 counterpoised on the balance by a similar one to eliminate the 

 effects of atmospheric changes. For each gram of carbon 

 dioxide 0*5 of a milligram was added for reduction to weight 

 in vacuum. This was the correction calculated for the solu- 

 tion of potassium hydroxide used which had a density of 1*38 ; 

 it was also found by experiment to be the same. The calcula- 

 tions are based on the atomic weights 12 and 16 of carbon and 

 oxygen respectively. The following are the results : 



* Loc. cit. 



