OF THE PARAFFINS AND THEIR MONOHALOGEN DERIVATIVES. 
3 
iodine chloride have values near 1 "S. The ratios of the specific heats of all seven gases 
were found to be unafiected by change of temperature over a wide range. 
Beanie (‘ Beihlatter,’ vol. 9, p. 503) made some experiments on the saturated 
vapours of ether, carbon bisulphide, chloroform, benzene, and water, by a modification 
of Kdndt’s method, but as he made no attempt to determine the densities of the 
vapours, his work does little more than show that sound is conducted freely through 
saturated vapours. 
P, A. Muller (Wied. ‘Ann.,’ vol. 18, p. 94) investigated the ratios of the specific 
heats of a large number of gases by a method devised by Assmann (Pogg. ‘ Ann.,’ 
vol. 85, p. 1). Muller assumes that alternate compressions and rarefactions, with a 
period of half-a-second in a globe holding about a litre of gas, are adiabatic. In the 
light of the work of Rontgen and Kundt on the effect of the size of the apparatus, 
it is evident that this cannot be the case, and we might expect Muller’s results to 
be too low. In almost every case where comparison is possible his result is lower than 
that obtained by methods recognized as trustworthy. 
The exj)eriments of Jager (Wied. ‘Ann.,’ vol. 36, p. 165) were intended to test 
the question whether y depends on the degree of saturation of the gas or not. He 
concludes that for the vapours of ether, alcohol, and water the degree of saturation 
has no effect on y, but the experiments are hardly accurate enough to be conclusive. 
Other papers on single gases are those of Kayser (Wied. ‘Ann.,’ vol. 2, p. 218), on 
Air, of Martini (‘Revist. Scient. Ind.,’* vol. 13, p. 146), on Chlorine, and of 
E. and L. Natanson, on Nitrogen Peroxide. 
It appears that the gases hitherto investigated have not been chosen with a view 
to elucidating the constitution of the molecule, and are not suitable for this purpose. 
Almost all are inorganic gases which, it is true, are easily prepared fairly pure, but 
are too irregular in their properties to lead to much of theoretical value. Each gas 
has peculiarities of its own which are not shared with others, and we have nothing 
corresponding to the homologous series of organic chemistry. It can hardly be 
doubted that the success of physico-chemical methods of late years would have been 
much less striking if inorganic bodies only had been available. 
Amongst the carbon compounds we have many series of gases or volatile liquids 
proceeding by regular increments of CHo to the molecule, the members of any one 
series showing such striking similarities in their properties as to point to similarity 
of constitution of the molecule. We have, too, the advantage of accurately deter¬ 
mined graphic formulae, and though we are not justified in regarding these as concrete 
representations of the molecule, yet the consistency with which the system of notation 
has been ajiplied to thousands of compounds shows that it has its basis in some 
physical fact, and makes it well suited to serve as the “ independent variable ” in 
expressing other properties as functions of the complexity of the molecule, 
For these reasons I have chosen the paraffins and their monohalogen derivatives as 
being simply related to each other, easily volatile, and stable. 
