222 re;ports of investigations and projects, 



to only one-third of i per cent. This indicates the interesting fact that the 

 heat of formation of the vapor from the elements is greater in those cases 

 where the heat of condensation is less, and vice versa. In the case of the 

 zylenes also the maximum deviation was only about 0.3 per cent, ortho- and 

 meta-zylene giving exactly the same values and para-zylene slightly less. 

 Stohmann found no difference among the three ; but he was much dissatisfied 

 with his determinations. As ortho-zylene boils at a temperature considerably 

 above meta-zylene and its heat of vaporization must therefore be greater, it is 

 apparent here also that the vapor which possesses the greater heat of con- 

 densation possesses the less heat of formation. In other words, the combin- 

 ing energy which is not used up in chemical combination seems to be available 

 for cohesive action. One is inclined to infer that chemical affinity and cohe- 

 sion are merely different manifestations of the same forces. This investiga- 

 tion will be continued in the near future and the effort will be made to obtain 

 as much light as possible upon the energy relations of these closely related 

 compounds. 



IV. The Heat of Neutralisation of Strong Acids and Strong Bases: 



Another highly important branch of thermochemistry concerns the phe- 

 nomenon of heat of neutralization. In view of the comparatively crude 

 methods which have been used by most of the experimenters upon this sub- 

 ject, revision seemed to be desirable, and the problem was undertaken with 

 the help of Dr. A. W. Rowe. The investigation is, as a matter of fact, by 

 no means as simple as it might seem. In the first place, the specific heats 

 of the solutions upon which the whole calculation depends must first be 

 determined with as great accuracy as the heat evolved during chemical re- 

 action, and the methods heretofore used for this purpose are by no means 

 satisfactory. The first step of the research was therefore the development of 

 an accurate and convenient method for determining the specific heats of 

 solutions, already mentioned in the last report. Further investigation im- 

 proved somewhat some of the details of this process, so that no great diffi- 

 culty is now in the way of determining specific heats within one-thirtieth of 

 I per cent. 



In studying the heat of neutralization itself two methods were adopted. In 

 the first place, concentrated alkali was allowed to mix with dilute acid, and 

 in separate determinations the heats of dilution of the various solutions to 

 the usual standard — i molecule of dissolved substance to 200 of water — were 

 found and applied to the results. In another set of determinations the dilute 

 acid and dilute alkali of this standard strength were caused to mix in two 

 concentric platinum cans, the inner one having contained in the first place one 

 of the liquids and the outer annular space having contained the other. 

 Great care is needed in effecting the mixture in order to be sure that the 

 heat is evenly distributed throughout the mass, and special precautions were 



