Dr; Andrews's Report on the Heat of Combination. 517 



In an early part of his memoir, Hess gives 38'85 for the value 

 of a, but this he afterwards changes to 46*94', still maintaining how- 

 ever the accuracy of the ratios. It is difficult to see how this can 

 be correct. The only experiment described by Hess on the combi- 

 nation of the anhydrous acid with water gave the number 305, which 

 bears to 46*94', not the ratio of 8 : 2, but nearly that of 6*5 to 2. 

 Abria obtained a still lower number for the combination SO3 with 

 HO. There can therefore be little doubt, if the experiments may be 

 relied on, that the first ratio is too high. It remains to be seen how 

 far the others have been confirmed by subsequent investigations. 



The multipliers of a for the three latter combinations given in the 

 preceding table are, according to Graham's experiments, 0*72, 1*35 

 and 1"18. These numbers agree with Hess's statement only so far 

 as to indicate that the heat evolved in the combination of SO3 HO 

 with HO is nearly the same as that evolved in the combination of 

 SO3 2H0 with 4H0. 



'' The experiments of Abria were performed by the direct method 

 'and with a similar apparatus to that employed by Hess. Adopting 

 the views of Hess as to the quantities of heat in the cases of combi- 

 nation being in simple relations to one another, he arrives nevertheless 

 at very different numbers for the ratios. In the next table I have 

 given Abria's theoretical whole numbers, as also the exact numbers 

 which result from his experiments. 



;, :w>.i3«da,saa - Theory. Experiment. 



f, ,, S63 +H0 iSa ,,. ,,fr()2a„, ,,, 



hnv. M- ?3 3H9 + H? • • • • f« 0-TTvOa -f,- MV" .bnooo. 



S03 4HO-fHO.... |« ........ O-SSohHy o'<' 



:. SO3 5H0 + HO ... . ia 0-22a, ,,„;^^^; 



In the three latter cases, the simple relations in the second co- 

 lumn are scarcely borne out by the experimental numbers. The 

 only agreement with the ratios given by Hess is in the combination 

 SO3 2H0 with HO, which, according to both experimenters, sets 

 free exactly half as much heat as the combination SO3HO with HO. 

 The value of a, given by Abria, is 39*33. 



; • : The latest experiments on this subject are those of Fabre and Sil- 

 bermann, from which I have calculated the following multipliers 

 for«:— ii"'J^ ^'^r 



,M^ . s-i SO3HO + HO 2-OOa I'^i^ J^ «^iifi» 



soJiJti)/ii :v/i.-.*j SO3 2HO4-HO 0-93« ^0 fc'jiJiJnuHp 



siUnr SO33HO + HO 0-53a ' ^^"^o 



ivM^f SO34HO + HO 0-32a ift.> 



SO35HO + HO 0-26a - 



Hess has also attempted to express by simple multiple relations 

 the quantities of heat disengaged in the formation of the hydrates 

 of nitric acid, but for the details of his results I must refer to the 

 original memoir. 



Combination of Acids and Bases. — In the same memoir Hess de- 



