15338 
From the dissociation constants found at the different temperatures, 
it follows that this constant attains in this acid a maximum between 
0 and 45°. *) 
4. Heat of combustion. 
Neither from glutaconie acid itself, nor from one of its homologues 
the heat of combustion is already known. We possess, however, 
trustworthy comparison material for aconitic acid (m.p. 191° with 
decomposition) *) 
HOOC — CH — C (COOH) — CH — COOH 
H 
and tricarballylic acid. We find in the literature: *) 
for tricarballylic acid: V,.,—= 517.0 resp. 517.3 Kal. 
for aconitic acid: 476.5 ,, 4815 „ 
405 „ ken 
The mean of these values found by SronMaxN and his co-workers 
and by Loveurntng, respectively (and of which the first, for various 
reasons, is very probably the most trustworthy one) is + 38 Cal. 
The usual difference in energy between a saturated alifatic acid and 
the correlated unsaturated (trans) acid is about 37 Cal. ©, whereas, 
according to investigations of Rorn and WattascH *), the heat of 
combustion of the cis-acid is always about 6 Cul. greater than that 
of the trans-acid. 
The heat of combustion of “normal” aconitic acid is, therefore, 
about equal (probably it will be somewhat smaller) to that, which 
starting from tricarballylic acid, we calculate for the ¢rans-acid. 
From the above we notice that glutaconic acid is connected very 
closely but not completely with the trans-acids. It thus stands nearest 
to the most stable of the two “labile” isomerides which, theoretically, 
was, of course, to be expected. 
b) Mutual transformations of cis-trans-isomerides. 
Bucuner*), starting from the ordinary glutaconie acid, has tried 
1) For the position of these maxima see Jones and Wuire: Amer. chem. Journ. 
44, and further. 
*) Of this acid is still known a ‘labile’ modification m.p. 173° (BLAND and 
THORPE: Soc, 101, 1490 (1912)). 
5) For these heats of combustion compare table 198 of LANDOLT-B6RNSTEIN-ROTH. 
4) WarLascH (Dissertation Greifswald 1913) accepted 45 cal; this value, 
however, is surely too high. 
5) Ber. 46 260 (1913). 
8) Ber. 27. 881 (1894). 
