222 REPORT—1890. 
the dissociation ratio of the components in the original solutions and 
the products (exclusive of the water) in the mixture respectively, W,, 
W,., W3;, the heats of dissociation, the amounts of heat necessary to com- 
plete the dissociation of each part would be W,(1—d,), W.(1—d,), and 
W,(1—d,) respectively. Hence, there being no work done, the heat 
developed in mixing would be 
N= —(1—d,)W, -(1—d,)W, +2+ (1—d,)W,, 
where « is the heat of formation of the water, deduced from the change 
of heat of neutralisation of HCl with temperature as 12950 cal,! 
In this way the following heats of neutralisation of acids were deter- 
mined and compared with the known values observed experimentally :— 
Heat of Neutralisation (with NaOH) at 21°5 
Name 
Calculated Observed Difference 
HCl. é , ; a 13700 13740 +40 
HBr. : : . 5 13700 13750 —10 
HNO, : a c : 13810 13680 —130 
CH,COOH : 5 : 13070 13400 +330 
C,H,COOH 5 5 : 13400 13480 +80 
C,H,COOH , : . 13750 13800 +50 
C,H,(COOH), . : 3 12240 12400 +160 
CHCI,COOH . : : 14980 14830 —150 
H,PO0, } : . 5 14910 14830 —80 
HOPOH, . : ‘ ‘ 15460 15160 — 300 
HF . : : 3 9 16120 16270 +150 
The table shows, among other things, that the explanation of the fact 
that some weak acids, as HF, HOPOH,, H;PO,, have higher heat of 
neutralisation than the strong acids, is to be found in the development 
of heat in dissociation shown by the table of p. 221. 
Another deducticn from the principles mentioned above is that the 
conductivity of an electrolyte may have a negative temperature co- 
efficient, if the temperature be sufficiently raised. The resistance of an 
electrolyte depends upon (1) the friction of the moving ions, (2) their 
number or the dissociation ratio, and both of these vary with the tem- 
perature. According to Ostwald’s dissociation formula, if 3 be the dis- 
sociation ratio, = 
(i—8 a 
and 
dlog.k_1 ,A W 
wwOrTt BPs 
Assuming, for the sake of simplicity, that the right-hand side does not 
vary with the temperature, and further, supposing that the electrolyte 
is only slightly dissociated, so that 6 is small compared with unity, and 
w being constant, we get 
2d Ns °— const. = —2b dt. 
Whence 
GaAge, 
1 12H,+0,=2H,0 + 27040 cal.; or H,H,H,H + 0,0, = 2H,0 + 27040 cal. 
