the Constitution of Carbon Compounds, 91 



Thomsen also points out that, whereas the difference 

 between the heats of formation of methane and methoxy- 

 methane or dimethyl ether is 65400 units, that between 

 methoxymethane and methylal — which is usually regarded as 

 dimethoxy methane — is 76110 units, and that between methy- 

 lal and methylic orthoformate — which is commonly represented 

 as trim ethoxy methane CH(OMe) 3 — is 79730 units. Compar- 

 ing the heat of formation of methylal, C 3 H 8 2 , with that of 

 methylethyl ether, C 3 H 8 0, there is a difference of 29500 

 units \ between methylic orthoformate, C 4 H 10 O 3 , and diethyl 

 ether, C 4 H 10 O. there is a difference of 2.29920 units; so 

 that the heat of formation is increased by the addition of an 

 atom of oxygen by 29500 to 29920 units. This value very 

 nearly corresponds to the difference between an alcohol and 

 the hydrocarbon from which it is formed, thus 



Methyl alcohol — methane = 29410 units. 

 Ethyl „ -ethane =29620 „ 

 Propyl „ —propane =30290 „ 



Thomsen therefore suggests that possibly the function of the 

 oxygen in bodies such as methylal and methylic orthoformate 

 is the same as that of the oxygen in alcohols. 



(12) Heat of Combustion of Aldehydes, Ketones, Acids, 

 Anhydrides and Ethereal Salts. — The observed heats of for- 

 mation of a number of these compounds are given in Table 

 VIII., and also the values deduced by subtracting the amounts 

 of heat which it may be assumed are developed in the formation 

 of the hydrocarbon radicals. 



The mean values which thus result, representing the heats 

 of formation of the characteristic groups in the aldehydes, 

 ketones and acids, are as follows : — 



Aldehydes . COH . . 65400 units 

 Ketones . . CO . . 54250 „ 

 Acids . . . COOH. . 119960 „ 

 It will be observed that 65400 + 54250 = 119650 : in other 

 words, the amount of heat developed in the formation of the 

 carboxyl group of acids is the sum of that developed in the 

 formation of the group COH and CO. Hence Thomsen con- 

 cludes that the aldehydes are unsaturated compounds of the 

 formula B, . C (OH), inasmuch as it is to be supposed that the 

 ketones and acids are respectively constituted as represented 

 by the formulas 



E 3 C:OandR.C:0(OH). 

 Deducting from the heat of formation of acetic anhydride, 

 284340 units, the value 6r + 2v, the difference (165940 units) 

 will represent the heat developed in the formation of the 



H2 



