174 



SCIENCE. 



[N. S. Vol. XXIII. No. 579. 



culty of freeing the alcohols entirely from 

 water. The same general rule holds for 

 many other organic compounds. 



In the case of several of the organic 

 liquids, the calculated degrees of freedom 

 can be reproduced by assigning 2, or some- 

 times 3, degrees of fredom to the hydrogen 

 atoms. 



Other such compounds can not be treated 

 with success so simply. 



We may examine a few of the solid or- 

 ganic bodies by the same method. Let us 

 begin with the three pairs of isomers, dex- 

 trose and levulose, mannite and dulcite, 

 resorcin (and hydroquinone) and pyro- 

 eatechin. The molecular heats of the two 

 members of each of these pairs differ by 6, 

 and we have suggested to us at once that 

 one characteristic diiference of two such 

 isomers may be that the molecule in one 

 of them may retain an individuality that 

 the molecule of the other loses, and may 

 vibrate about its position of equilibrium 

 as a whole, so that the value of 6 will con- 

 tain a = 6, while that of its isomer will 

 not. If we admit this, we, obtain values 

 of the internal degrees of freedom which 

 are satisfied by assigning one degree of 

 freedom to each atom. 



Dextrose, levulose. 



Mannite. dulcite... 



Eesorcin, py rocate- 



chin 



QHiA 

 CeHiA 



CsHfiOj 



In the cases of cane sugar and anhydrous 

 milk sugar we can not assume the differ- 

 ence between the molecular heats to be due 

 to the cause previously assigned, but if we 

 examine the structure of these large mole- 

 cules, we shall find that four of the carbon 

 atoms are differently connected in the mole- 

 cule from the other eight. If Ave suppose 

 a^O, and assign 2 degrees of freedom to 

 each of the group of eight carbon atoms in 

 the one case, and to each of the group of 

 four carbon atoms in the other case, we 

 obtain a fair agreement with the calculated 

 numbers of degrees of freedom. 



Cane sugar CiCgHjjOn 



Anhydrous milk 



sugar CjCaHjjO,, 



In levulose and dextrose one of the car- 

 bon atoms is peculiarly connected with the 

 other constituents of the molecule. If we 

 assign to it 2 degrees of freedom, we obtain 

 an exact agreement with- the calculated 

 number of degrees of freedom. 



When these organic solids are dissolved 

 in water or alcohol, their apparent molec- 

 ular heats, that is, the molecular heats 

 calculated for them from the specific heats 

 of th'eir solutions, on the hypothesis that 

 the specific heat of the solvent remains 

 unchanged, are constants for all ordinary 

 concentrations, and differ with the different 

 solvents. These apparent molecular heats 

 are generally greater than those of the 

 same substance in the solid state. It may 

 be that the dissolved molecules have so 

 united themselves with the surrounding 

 water as to weaken the bonds of the water 

 molecules and have thus increased their 

 degi-ees of freedom; but it is also possible 

 that the degrees of freedom of the dissolved 

 molecules themselves have been increased 

 by the process of solution. If we adopt 

 the latter hypothesis, we may construct 

 schemes apportioning the degrees of free- 



