W. G. Mixter — Thermal Constants of Acetylene. 13 



Art. IY. — The Thermal Constants of Acetylene • by W. G. 



Mixter. 



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



Some years ago the writer observed* that the thermal con- 

 stants of acetylene found by different observers varied widely, 

 and that his result for the heat of dissociation of the gas was 

 considerably higher than the calculated value. It was evident 

 that a complete investigation of the matter involved a study of 

 the components of acetylene. Accordingly the heat of com- 

 bustion of hydrogen was determined. f The results of Thomsen, 

 Schuller and Wartha, Than, and the writer gave a value with 

 probably a small error. The heat found on burning acetylene 

 carbon J was about two per cent higher than that of the ordinary 

 forms of amorphous carbon. The thermal constant of this 

 allotrope of carbon is essential in calculating the heat of disso- 

 ciation of acetylene. 



For the thermal work on carbon acetylene carbon was pre- 

 pared with care, and at the same time new determinations of 

 the heat of dissociation of acetylene were made. The bomb 

 used was similar to the one described in the paper on carbon 

 but with electrodes in the upper end of the stem. Both bombs 

 were alike in external volume and surface. One bomb was 

 filled with pure hydrogen and exhausted and counterpoised by 

 the other bomb and the needed weights. Then it was filled 

 with dry acetylene from carbide and at a pressure of ten or 

 twelve atmospheres. Next 100 cc of the gas in the bomb were 

 passed into a eudiometer and the acetylene determined by 

 means of ammoniacal cuprous chloride. It varied in the different 

 experiments from 98*6 to 99 per cent. Finally the weight was 

 noted. The water equivalent of the calorimeter was found as 

 described in the paper on carbon. 



Experiment 1. — Acetylene, 6*3162 grams ; water, 3160*0 

 grams ; water equivalent of calorimeter, 285*2 grams ; water 

 equivalent of hydrogen and carbon formed, 2*1 grams. Total, 

 3447*3 grams. 



Minutes. Temperature. Temperature interval. 



18-204 



1 18*207 



2 18*210 21*995 — 18*21 +0*01 = 3*775° 



3 21*8 



4 21-9 Heat observed, 3447*3 X 3*775 = 13014° 



5 31*97 



6 21*977 For 1 gram "of acetylene 2060 c 



7 21-975 



8 21-973 



9 21-970 



10 21-966 



11 21*962 



* This Journal., xii, 347, 1901. + Ibid., xvi, 214. % Ibid -> xix > 434 - 



