140 STORRS AGRICULTURAL EXPERIMENT STATION. 
employed to keep the temperature of the room exactly constant. 
The stirrer is moved by a small motor, which is so regulated as 
to make the movement the same for all determinations. Berthelot 
uses a motor for the stirring, but conducts the combustion in the 
laboratory rooms where other work is done and without special 
arrangements to insure uniform temperature. 
The Berthelot bomb calorimeter serves its purpose admirably. 
It is comparatively simple, easily handled, and does not get out 
of order when properly cared for. Practically all kinds of ordi- 
nary organic compounds are completely oxidized when the proper 
excess of oxygen is used at an initial pressure of 25 atmospheres. 
With an accurate thermometer the rise in temperature of the 
water is measured with great accuracy. The corrections, of 
which the chief is the thermal water equivalent of the apparatus, 
are not particularly difficult to determine. The skill and care 
required in the manipulation are not beyond any thoroughly 
expert operator, and the results are very satisfactory indeed, as 
may be seen by comparing those obtained by Berthelot and 
Stohmann in determining the heats of combustion of the same 
material in their respective laboratories. 
The steel of which the bomb is made is especially exposed to 
corrosion. Berthelot protects the outside of the bomb by plating 
with nickel which serves the purpose very well, as water and air 
are practically the only corrosive agents to which it is exposed. 
But with the interior the case is very different. The oxygen at 
high pressure is very active in itself. The carbon, sulphur, and 
phosphorus of the substances burned are completely oxidized, 
and carbonic, sulphuric and phosphoric acids are formed. Indeed, 
Berthelot has shown that the apparatus may be used for deter- 
mining carbon, sulphur and phosphorus in these forms. More 
or less of the free nitrogen which is mingled with the oxygen 
used in the combustion and perhaps, at times, some of the nitrogen 
of the substance burned is oxidized and forms nitric acid. It is 
necessary that the inner surface be covered with some substance 
which will resist these acids as well as the oxygen. Such materials 
are easily found, but the practical difficulty has been to find an 
inexpensive lining which will insure permanent protection to the 
steel. In Berthelot’s first bomb, electro-plating with platinum 
was tried, but the plantinum soon began to scale off. Aftera 
few combustions gold was substituted for platinum and with 
better success, but it has not been used with oxygen under 


