50 
CHEMISTRY: RICHARDS AND DAVIS 
IMPROVEMENTS IN CALORIMETRIC COMBUSTION, AND THE HEAT 
OF COMBUSTION OF TOLUENE 
By Theodore W. Richards and Harold S. Davis 
WOLCOTT GIBBS MEMORIAL LABORATORY, HARVARD UNIVERSITY 
Read before the Academy. November 14, 1916 
The object of this investigation, which is part of a much larger 
program, was to secure further more precise knowledge of the heat of 
combustion of typical compounds of carbon, and further development 
of the methods of determination. ^ The work herein described followed 
directly after that detailed in the recent communication published with 
Dr. Frederick Barry; and the methods and apparatus resembled in 
most respects those already explained. Having profited by the experi- 
ence of the earlier work, we were able to improve upon some of its 
details. Especial emphasis will be laid upon the improvements. 
The method consisted in the successive combustion of toluene and 
a standard substance in the Berthelot bomb as modified by Atwater 
and Benedict, in oxygen under about 22 atmospheres pressure. The 
rise of temperature of the colorimeter containing the bomb was paral- 
leled in the environment, so that no correction for cooling was needed. 
That this adiabatic method is capable of giving excellent relative re- 
sults is shown by the series of investigation conducted at Harvard 
University; its absolute accuracy is proved by the recent careful work 
of the Bureau of Standards by H. C. Dickinson and his assistants.^ 
The general assemblage of apparatus is adequately described and de- 
picted in the most recent of the preceding papers, and the reader is 
referred to these as regards minutiae. 
The details in which improvements were instituted were as follows: 
the mode of sealing the bomb, the mode of providing for the well regu- 
lated and complete combustion of the volatile substance; the mode of 
ignition; the automatic control of the temperature of the environment 
by a special 'syn thermal regulator;' and the analysis of the residual 
gases for traces of unburned carbon monoxide. These several topics 
are discussed in order below, and finally the results for naphthalene 
and toluene are given. Other substances also were burned, but the 
details concerning these will be reserved for another communica- 
tion. 
The closing of the bomb. — The bomb was sealed by a washer of lead, 
sunk in a suitable circular slot and covered by a continuous round plate 
of gold foil (0.4 or 0.5 mm. thick) which protected the whole inside of 
