1239 
higher in the case of M, than in that of M,. Such will be the ease 
if M, consists entirely of a-cadmium. If B- and y-cadmium are 
simultaneously present (this represents the general case) the difference 
will be less than 739 gram calories per gram atom. 
4. Tu. W. RicHarps and Buraess') found that the heat of reaction 
between HCl. 200 H,O and cadmium which has been electrolytically 
deposited, (y-cadmium) is 17200 gram calories (at 20° C) per gram 
atom of the metal. In this case the error would be 4.3°/, in maximo. 
But even if it should reach only a small fraction of this value it 
would surpass the experimental errors, as thermochemical measurements 
can be carried out to-day with a precision of some tenths of one 
per cent. From this we may conclude that the presence of the 
different modifications must be taken into account. 
Up to the present this could not be done, so that all the heats 
of reaction of the metals determined hitherto are to be considered 
as fortuitous values. 
5. This is also true of the figures found by Junius TuomsenN®) for 
the heat of reaction ‘of cadmium with different solutions of HCI, as 
he used the metal in the form of plates. The metal had been melted 
and consequently contained unknown quantities of a-, ?-, y-cadmium *). 
6. What has been said here concerning cadmium evidently holds 
also for the other metals. 
7. All thermochemical values which have been ealculated on the 
basis of these erroneous values, evidently include the same errors: 
they are fortuitous values. 
8. The measurements of TH. W. RicHarps and Burarss, cited 
above, which have been partly redetermined by E. E. SOMERMEIER ®), 
indicate that the previous thermal treatment of the metal experimented 
with plays a role. 
As these results are not strictly comparable amongst themselves, 
we shall not discuss them here. 
9. The true heats of reaction of the metals, which represent 
1) Journ. Americ. Chem. Soc. 32, 431, 1176 (1910). 
*) Thermochemische Untersuchungen 3, 277 Leipzig (1883). Comp. Tu, W. Rrenarps 
and Burgess, Journ. Americ. Chem. Soc. 32, 431 (1910). 
3) Comp. our paper Zeitschr. f, physik, Chemie 89, 287 (1915), 
4) Phys. Rev. (2) 1, 141 (1913). 
