1893.] Specific Heats of Paraffins and Derivatives. 101 



the fact that not the whole of the field surrounding the wires lies in 

 the water. 



The uncertainty due to this stray field might be easily avoided in 

 one way, namely, by making one wire into a tube surrounding the 

 other and using this tube also as the jar for the electrolyte. This was, 

 in fact, the arrangement originally intended to be adopted. Several 

 disadvantages attended it, however, and led to its final rejection in 

 favour of the simple wires and glass jar. First, such a condenser 

 reflects under all circumstances a considerable portion of the incident 

 energy.* Secondly, the variation of the position of the top surface 

 of the electrolyte relatively to the top of the jar would introduce 

 fresh interference phenomena. This appeared directly from the work 

 of Mr. Barton to which I have already had occasion to refer. Lastly, 

 the large surface of metal in contact with the liquid would render 

 distilled water rapidly impure. 



This investigation was carried out in the Physical Institute of the 

 University of Bonn. I desire particularly to express my thanks to 

 Professor Hertz for his most useful advice and suggestions. 



VII. " On the Ratio of the Specific Heats of the Paraffins and 

 their Monohalogen Derivatives." By J. W. CAPSTICK, 

 M.Sc. (Viet.), B.A. (Camb.), Scholar and Coutts-Trotter 

 Student of Trinity College, Cambridge. Communicated by 

 Professor J. J. THOMSON, F.R.S. Received May 25, 1893. 



(Abstract.) 



The . experiments were undertaken to find whether the internal 

 energy of the molecules of organic gases, as deduced from the ratio 

 of the specific heats, showed any regularities corresponding to the 

 chemical resemblances symbolised by the graphic formulae. 



The paraffins and their monohalogen derivatives are very suitable 

 for the purpose, as their chemical relations to each other are simple, 

 they are easily volatile, and are stable enough to be unaffected by 

 ordinary purifying agents. 



From the ratio of the specific heats we can calculate the relative 

 rates of increase of the internal energy and the energy of translation 

 of the molecules per degree rise of temperature, and, the aim of the 

 experiments being to compare the rates of increase of the internal 

 energy of different gases, it was decided to keep the translational 

 energy constant by working at a constant temperature. Con- 

 sequently the determinations were all made at the temperature of 

 the room. 



The ratio of the specific heats was calculated from the velocity of 

 * J. Eitter von Geitler, Doctor-Dissertation, Bonn, Jan., 1893. 



