the Constitution of Carbon Compounds. 93 



— one from absolute alcohol and crystallized acetic acid, the 

 other from ethyl iodide and argentic acetate — boiling at 

 77°-4— 77°'5, the heats of combustion of which were 548080 

 and 549250 units, respectively. The value thus arrived at, 

 however, is about 12000 units lower than that found for the 

 allied ethereal salts, such as the metameric propylic formate, 

 for example. Thomsen is therefore inclined to think that the 

 formula CH 3 . COOC 2 H 5 does not correctly represent the con- 

 stitution of ethylic acetate, as the heat of formation of such 

 a compound would be 253880 units, or 12030 units less than 

 the value found experimentally — a difference of over two per 

 cent, of the heat of combustion. Assuming the formula to be 

 CH 3 . CH(OH) . CO . CH 3 , and calculating the heat of forma- 

 tion with the aid of the constants previously deduced for acids, 

 aldehydes and ketones, the value found, viz., 



7r + 3^ + 54250 + 65400 = 267250, 



differs by only 1340 units, or a quarter per cent, of the heat 

 of combustion, from the theoretical number. 



Thomsen leaves unexplained for the present the cause of 

 the discrepancy in the case of methylic and isobutylic 

 formates ; he does not regard it as remarkable that the value 

 for the allylic salt should be somewhat abnormal, as in other 

 cases values are found for allyl compounds which differ 

 somewhat from those for corresponding compounds of 

 C w H 2n+ i radicals. 



(13) Heat of Formation of Nitrogen Molecules. — Thomsen 

 bases his determination of the heat developed in the formation 

 of nitrogen molecules from nitrogen atoms on the argument 

 that probably, as in the case of carbon, the two atoms are 

 held together by single affinities. Assuming that in nitrogen 

 peroxide, N 2 4 , the nitrogen atoms are directly associated as 

 represented by the formula 



or bv the formula 



0\ /O 



O— N— O 



i-U- 



the amount of heat absorbed in converting the peroxide into 

 nitrogen dioxide (N0 2 ) molecules is the quantity sought to be 

 determined. Xow, according to Berthelot and Ogier, the heat 

 of dissociation of nitrogen peroxide between 27° and 198° is 

 10608 units ; as about 20 per cent, is already decomposed at 



