Page:Outlines of Physical Chemistry - 1899.djvu/192

 174 OUTLINES OF PHYSICAL CHEMISTRY

Julius Thomsen's System

This author believes that we can deduce the quantity of heat necessary for the volatilisation and isolation of an atom of carbon (volatilisation and isolation of the atoms contained in 12 grams of carbon). His system is based on the data :

(C, 0) = 29*29 Cal. ] for amorphous carbon and under

and on the hypothesis, a priori quite admissible, that the four atomicities of carbon are identical and, consequently, that by the fixation of the first and of the second oxygen atom the same quantity of heat is evolved. At first sight this is not apparent, on the contrary the thermal effects are very different (29*29 and 67*67 Cal.) ; but this is due to the fact that the fixation of the first oxygen atom must furnish the heat necessary for the isolation of the carbon atoms. This isolation absorbs 67*67-29*29 = 38*38 Cal.

Thomsen then proceeds to determine the thermal effect developed by the different relationships which are esta- blished between the atoms in organic molecules. For the hydrocarbons (all the products being supposed gaseous and at the temperature 18°) he finds :

Under constant pressure Und votamf"*

��Heat of Heat of Heat of

combustion formation formation

CH 4. 211-93 Cal. 2175 Cal. 21-17 Cal.

Oft. . 31005 „ -47-77 „ -4777 „

C^. . 333-35 „ - 2-71 „ - 329 „

C 2 H 6. . 370-44 „ 28-56 „ 27-40 „

1 To discuss J. Thomsen's system we must admit his fundamental data for the meantime :

(EL,, 0) = 68-36 Cal. (liquid water) (C, O.j = 96*96 „ (for amorphous carbon) (C, 0) = 29*0 „ under constant pressure (C, 0) = 29*29 „ under constant volume. This last figure is larger than the second last on account of an external work equal to J (0-58) Calories being avoided under the conditions of the experiment. See page 153.

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