Constitution of Isomeric Solutions. 303 



mixture " A " is changed into a fixed product, having the 

 same amount of voltaic energy as that produced by the 

 ingredients of " B." 



With regard to the statement that " the final division of 

 the base between the two acids is the same, whether the soda 

 were originally present as sulphate or nitrate," the present 

 research indicates that this is only true, provided the mix- 

 ture of sulphate of sodium and nitric acid has been sub- 

 jected to such conditions or influences, either during or after 

 its preparation, as decompose and convert it into the same 

 product as that of a mixture of nitrate of sodium and sul- 

 phuric acid. 



Whilst there is greater voltaic energy in the mixture " A," 

 there is more molecular momentum in the one "B;" and 

 whilst the chemical change in "A" may be retarded by low 

 temperature or dilution, it cannot be much prevented in " B" 

 by either of these causes or by both combined. In " A " the 

 chemical change which occurs during mixing only proceeds 

 to a certain stage, if suitable precautions are taken ; in " B " 

 it proceeds its entire course, and apparently with greater 

 velocity. 



The fact that by using weaker and colder solutions of the 

 separate ingredients of the mixture " A," a larger amount of 

 voltaic energy in the product is obtained, proves that the 

 amount of chemical change which occurs during mixing is a 

 variable quantity, and suggests that it may be still further 

 reduced. The larger the amount of voltaic energy of the 

 freshly-made mixture, the smaller is the amount of chemical 

 change which has occurred during the mixing. As the 

 freshly-made mixture gradually loses voltaic energy at 20° C, 

 the nitric acid gradually expels sulphuric, the proportion of 

 nitrate of sodium increases, and that of sulphate decreases. 



Loss of voltaic energy does not always coincide with loss 

 of thermal energy ; for instance, in making the mixture " A" 

 heat is absorbed, but in making the one " B " heat is evolved ; 

 whilst in both cases the amount of voltaic energy is diminished. 

 In making " A " the loss of energy is 94*86 per cent., and in 

 making "B" 97'70 per cent, (see Table X.). 



The " voltaic balance " is a very convenient instrument for 

 detecting and measuring molecular changes in dissolved 

 chemical compounds. 



Z2 



