378 THE PRODUCTION OF HEAT, LIGHT, AND ELECTRICITY 



is worthy of note that certain anaerobes are able to work with the utmost 

 economy. The anaerobic respiration of obligate aerobes is too feeble to 

 maintain life, but nevertheless it produces sufficient heat to raise the tem- 

 perature of plants massed together from o-i to 0-3 C. above that of similar 

 masses of dead plants, whereas in the presence of oxygen a difference of 

 temperature of from 5 to i6C. would be shown. 



Eriksson l in obtaining these results took ample precautions to ensure the 

 absence of all free oxygen, and also the absence of micro-organisms, by washing 

 and by rapid observation 2 . During alcoholic fermentation the fermenting liquid 

 may rise ioC. in temperature 3 . The decomposition of a gram-molecule (160 

 grams) of dextrose into alcohol and carbon dioxide yields 33 kilogram-calories, 

 i.e. sufficient heat to warm a litre of water from 4 C. to 37 C. 4 The complete com- 

 bustion of dextrose yields, however, twenty times more heat, namely 673-7 kg.-calories. 

 During alcoholic fermentation traces of other substances are formed in addition to 

 alcohol and carbon dioxide. Hence the theoretical and the observed amount of 

 heat produced will not necessarily correspond. Bouffard found that 180 grams of 

 dextrose when fermented only produced 23-3 kg.-calories instead of the estimated 

 32-07, but this may possibly have been due to the difficulty of preventing the loss of 

 heat by radiation and conduction. 



Alcohol and carbon dioxide are also produced during the intramolecular re- 

 spiration of aerobes ; but, since other decompositions occur simultaneously, no 

 theoretical calculation can be made of the amount of heat produced from the 

 quantity of alcohol and of carbon dioxide formed. It is possible, however, that 

 investigations of this kind may throw light upon the phenomena of intramolecular 

 respiration. The liberation of carbon dioxide from an oxidized compound may be 

 an endothermic change (decomposition of carbonates) or only a feebly exothermic 

 one (fermentation of alcohol), so that even when equal quantities of carbon dioxide 

 were produced the anaerobic production of heat would be considerably less than the 

 aerobic one, in which the process is practically one of complete combustion, and 

 the respiratory materials contain relatively little or no combined oxygen. 



The decomposition of i gram-molecule of dextrose into 2 gram-molecules of 

 lactic acid liberates 14-7 kg.-calories, and its splitting into i gram-molecule 

 of butyric acid and 2 gram-molecules of hydrogen sets free 10-9 kg.-calories'. 



1 Eriksson, Unters. a. d. bot. Inst. zn Tiibingen, 1881, Ed. i, p. 105. 



2 Pasteur (Compt. rend., 1872, Bd. LXXV, p. 1056, Etude s. la biere, 1876, p. 261) observed 

 a marked rise of temperature in fruits and fleshy roots in the absence of oxygen, but this was 

 probably due to the development of anaerobic bacteria. 



s Cf. Dubrunfaut, Journ. f. pract. Chemie, 1856, Bd. LXIX, p. 444; Fitz, Ber. d. chem. Ges., 

 J 873. P- 57; Brefeld, Landw. Jahrb., 1876, Bd. V, p. 300; Eriksson, I.e.; Nageli, Theorie d. 

 Gahrung, 1879, P- 5 8 '> Bouffard, Compt. rend., 1895, T. CXXi, p. 136. 



* Cf. Bouffard, I.e.; E. Duclaux, Traite de Microbiologie, 1898, Bd. II, pp. 77, 739. The 

 heats of solution are allowed for in the above value, but otherwise it would be reduced to 

 22> 3 kg.-calories, the difference between the heat of combustion of dextrose (i gram-molecule = 

 ^73-7 kg.-cal.) and of alcohol (2 gram-molecules = 651.4 kg.-cal.). 



* Cf. R. O. Hertzog, Zeitschr. f. physiol. Chemie, 1903, Bd. xxxvil, p. 383, and textbooks of 

 Physical Chemistry. 



