
NEW FORM OF BOMB CALORIMETER. 139 
of platinum. The internal capacity is about 300 cubic centi- 
meters and it holds, under a pressure of 24 atmospheres, 7 liters, 
or, in round numbers, to grams, of oxygen. The cover fits into 
the top of the cylinder after the manner of a stopper. It is 
pressed in and held very tightly by an outer cap or collar which 
screws on to the outside of the cylinder at the top. The fittings 
have to be made with the greatest care in order to prevent the 
escape Ofygas. The material to be burned is shaped into a small 
cake by means of a powerful press and is held in a platinum 
capsule, ‘This capsule is sustained by a platinum wire which is 
fastened to the under side of the cover. Another platinum wire 
passes through the cover, from which it is insulated by gutta 
percha, or other appropriate material. These two wires are so 
arranged that they are easily connected by a piece of fine iron 
wire hanging over the substance to be burned in the platinum 
capsule. An electric current passed through the platinum wire 
heats the iron wire to a temperature where it burns in the oxygen 
and, melting, falls upon the substance so as to ignite it. An 
arrangement at the top of the cover provides for admitting the 
oxygen. The oxygen is introduced either with the aid of a 
compression pump, or, more conveniently, from iron or steel 
cylinders, in which it is held under sufficient pressure. Both 
Berthelot and Stohmann use such cylinders without the aid of a 
pump. Experience has shown that it is desirable to have fully 
three times as much oxygen present as is theoretically necessary 
for the combustion. 
The quantity of water in which the bomb is immersed ts gener- 
ally about 2 liters. It is contained in a calorimeter cylinder of 
brass or other metal. A stirrer, not easily described without a 
diagram, plays between the bomb and the cylinder in such a way 
as readily to mix the water and insure uniform temperature after 
the combustion. The outer cylinders which are employed by 
Berthelot and Stohmann to protect the apparatus from gain or loss 
by heat outside, as above described, are made of copper. They 
find that two concentric cylinders so arranged as to hold a 
layer of water between them, the inner being large enough to 
leave a considerable air space around the calorimeter cylinder, 
suffice for accurate work. 
In Stohmann’s laboratory the arrangements to insure accuracy 
are quite elaborate. ‘The work is done in a basement room sur- 
rounded by very thick walls of stone. Special devices are 
