the Constitution of Carbon Compounds. 79 



the difference between the heat of combustion of phenol and 

 that of the homologue when both are in the same state of 

 aggregation. 



(3) Equality of the Four Affinities of Carbon. — On reference 

 to TabJe I., it will be noticed that on passing from methane 

 to ethane or methylmethane, from ethane to propane or 

 dimethylmethane, and thence to tri- and tetramethylmethane, 

 the heat of combustion increases at each step to the same 

 extent : the displacement of hydrogen by methyl, in fact, 

 appears always to involve the same development of heat; and 

 hence it may be inferred that the four affinities of the carbon 

 atom are of equal value. Thomsen also finds that ethylene 

 and ethylidene chlorides have identical heats of combustion 

 (272000 units); and that there is practically no difference 

 between those of allyl chloride, CH 2 .CH.CH 2 C1 (442500 

 units), and the isomeric monochloropropylene, CH 2 . CC1 . CH 3 

 (441190 units). These facts, and also the practical identity 

 of the heats of combustion of isomeric phenols established 

 by Stohmann's determinations (Table II.), may be adduced 

 as confirmatory of the above deduction. 



(4) Heat of Combustion of Gaseous " Atomic " Carbon and 

 the Amount of Heat required to separate "Doubly -linked " Car- 

 bon Atoms. — On comparing the heats of combustion of bodies 

 differing in composition by one or more atoms of carbon 

 (Table III.), it is seen that the heat of combustion of carbon 

 in its compounds must be greater than that of the ordinary 

 amorphous variety of carbon (96960 units). The average 

 value deduced from fourteen comparisons is 121085 (in round 

 numbers 121090) units, the extremes being 115610 units (the 

 difference between ethyl- and allylamine), and 125750 units 

 (the difference between diethyl and diallyl ether), — a somewhat 

 wide range be it remarked. 



In the instances given in the Table the comparison is in- 

 stituted between a saturated and an unsaturated compound, 

 the latter being formed from the former by the addition of a 

 carbon atom which, according to the popular view, becomes 

 doubly linked with another carbon atom ; the amount of heat 

 developed by this "double-linking'" of two carbon atoms (v 2 ) 

 is the difference between the heat of combustion of gaseous 

 " atomic » carbon (/. d) and the factor 121090, i.e. 



/.C 1 = 121090units + v 2 . 



Now if carbon dioxide were capable of combining with an 

 atom of carbon, it is to be supposed that it would form an 

 unsaturated compound, CO : CO, bearing the same relation 

 to it that ethylene bears to methane, and that the heat of 



