Constitution of Isomeric Solutions. 291 



Na 2 S0 4 , 2HN0 3 — NaNOs, HN0 3 — and 2NaN0 3 , Na 2 S0 4 ; 

 besides the more complex aggregates and the total aggregate 

 formed by the feebler chemical union of these compounds 

 with each other (see Table IX.; also " A Method of Detecting- 

 dissolved Chemical Compounds and their Combining Propor- 

 tions/' Roy. Soc. Proc. vol. xlv. p. 265). The following are 

 the relative amounts of voltaic energy of some of these sub- 

 stances : — 



Table II. 





Yoltaic 



H 2 S0 4 . Between 3,690,476 and 4,111,466 at 19° C. 



energy. 

 Airerage3,900,941 



HNO3 3,039,215 



3,369,565 



,, 



3,204,295 



Na 2 S0 4 1,914 



2,126 



13 



2,020 



NaN0 3 155 



177 



12 



163 



NaHO (8004+1996 \ , 2U<m 

 per cent. Na 2 0O 3 ) . J ~ Z0 ^ yd4 



-287,037 



17 



-270,985 



Speaking of thermochemical measurement in this case, 

 L. Meyer states " according to J. Thomsen's experiments, 

 although the action of one acid upon the other, and the action 

 of the salts on each other, do not produce any effect capable 

 of measurement, still each acid produces a greater or less 

 thermic effect with its own salt." And in the case of decom- 

 position of a salt by an acid, he says " the extent of the de- 

 composition can be determined from the value of the thermic 

 effect." " But for this determination it is necessary to make 

 an extensive series of experiments, showing the thermo- 

 chemical effect of each pair of the substances in question. 

 The action of each acid on the base must be separately deter- 

 mined, then the action of each acid on its own salt, and also 

 on the salt of the other acid, and finally the mutual action of 

 the two acids." a The greatest possible care has to be exer- 

 cised in each individual determination, in order that the result 

 may be trustworthy ; if due caution is not observed utterly 

 false results are easily obtained." " Secondary thermic re- 

 sults are also produced by the mutual action of the other 

 bodies." (' Modern Theories of Chemistry,' pp. 466-468.) 

 According to J. Thomsen, the value of the thermal change 

 attending the reaction of dilute sulphuric upon dilute nitric 

 acid " is so small that it cannot be accurately determined " 

 {- Principles of Chemistry,' p. 435). 



If, however, we employ the " voltaic-balance " method 

 instead of the thermochemical one, not only the chemical 

 union of each of the acids with each of the salts, and with 

 one another, and the individual salts with each other, is clearly 

 shown by a depression of energy, but even that of Na 2 S0 4 , 

 2HNO3, with 2NaN0 3 ,H 2 S0 4 , and of still more complex 



