1895.] On the Electrolysis of Gases. 255 



3. The combination of the positively electrified hydrogen atoms 

 with the negatively electrified chlorine ones to form hydrochloric 

 acid. 



In that class of chemical action where the atoms retain their charge 

 (2) is absent, so that if the change in energy occurring in the pro- 

 cess (2) were considerable compared with the changes occurring in, 

 processes (1) and (3), the thermal effects of the two types of chemical 

 combination ought to differ considerably. If the changes in energy 

 occurring in the process (2) had a great preponderance over those 

 occurring in (1) and (3), the thermal effects produced by the com- 

 bination of two elements ought to follow very simple laws. For if 

 2{H} is the excess of the energy of an atom of hydrogen charged 

 with the negative electron over the energy of the atom charged with 

 the positive electron, 2 {01} the excess of the energy of an atom of 

 chlorine charged with the positive electron over the energy of the atom 

 charged with the negative electron, then if we could neglect the 

 energy changes in (1) and (3) compared with those in (2), the 

 mechanical equivalent of the heat developed when a molecule of 

 hydrogen combines with one of chlorine to form two molecules of 

 hydrochloric acid would be equal to 2{H} + 2{C1}. Thus we see that 

 if the energry changes in (2) preponderated largely over those in (1) 

 and (3), the heat produced when an element A combined with another 

 element B to form the compound AB, could be expressed as the sum 

 of two numbers {A} and {B}, where {A} depends solely on the 

 element A, {B} solely on the element B. In some cases of chemical 

 combination between dilute solutions there seems evidence that the 

 heat produced can be expressed in this way (see Lothar Meyer, " The 

 Evolution of the Doctrine of Affinity," ' Phil. Mag.,' vol. 23, p. 504), 

 but when we attempt to apply the same law to combination between 

 gases, it seems utterly to break down, indicating that in such cases 

 the greater part of the changes in energy occur in the splitting up of 

 one set of molecules and the subsequent formation of others. This 

 view seems to be supported by the phenomena attending the discharge 

 of electricity through rarefied gases, for the smallest difference of 

 potential which can send a discharge through an electrified gas 

 (which we have reason to believe involves the splitting up of 

 molecules into atoms), is very many times the electromotive force 

 required to liberate the ions from an electrolyte, though the latter 

 process requires changes in the electrical charges on the ions. These 

 reasons seem to indicate that we can hardly expect to get any clear 

 indication of the charges carried by the atoms in gaseous compounds 

 from the study of the thermal changes which occur when gases enter 

 into chemical combination. 



Vapours of Organic Compounds. These show very interesting 

 differences between the spectra on the two sides of the plate when 



