NEW LAW IN THERMOCHEMISTRY 9 



and hydrogen burned ; but the divisor in all three formulae has 

 the same value and gives the same quotient. The first and 

 most elaborate form is the one to be preferred, for the reason 

 that it gives in detail all the terms of the original equations. 

 In it the constant appears as a function of all the changes which 

 have taken place ; the substances produced being indicated with 

 the plus sign, while the substances destroyed are minus. The 

 other formuhe may be easier to apply, but they are much less 

 simple to interpret. 



In the thirty-three compounds so far tabulated, the mean value 

 of the quotient is 13828 calories. This is sensibly identical in 

 magnitude, within the limits of experimental uncertainty, with 

 the neutralization constant, which is commonly put at 13700 

 calories, with actual measurements ranging from 13 600 to 13 900. 

 The latter is purely chemical in its origin, uncomplicated by 

 extraneous physical considerations ; and it represents the thermal 

 value of the simplest of all unions, one bond joining two ions. 

 In short, it seems to be a definite unit of thermochemical change, 

 of which the quantities discussed in this paper are multiples, 

 and by whose aid the original equations, hitherto indeterminate, 

 may be satisfied. Let us examine the general formula a little 

 more closely and in detail. 



If now we take the constant, instead of the calorie, as our 

 unit, the fundamental formula may be written 



= I, or one unit, 



\2a -\- 6b — c — %n 



and hence, \2a -{- 6b — c —^n = ^K. That is, each molecule 

 of a or CO2 produced by a combustion has a value of 12 units. 

 Each molecule of water is represented by 6 units, each molecule 

 of oxygen by i, and each atomic linking in a single molecule 

 of the substance under investigation by f or 2 units. These 

 quantities represent the actual heat of formation of the several 

 molecules from gaseous, dissociated atoms^ and when they are 

 introduced into the original equations, the latter are satisfied. 

 The final value of the constant, which, for convenience, we may 

 call the Henotherm^ cannot be fixed until we have completed 



'The prefix hc7to is from the Greek verb kvou, to unite. 



