52 
CHEMISTRY: RICHARDS AND DAVIS 
Other precautions concerning the makeup and treatment of the bomb 
were similar to those already described in previous investigations. 
Mode of enclosing and igniting volatile liquids in thin-walled glass 
bulbs. — For enclosing the Kquids to be burned, very thin bulbs, hold- 
ing about 1 cc. and weighing about 0.4 g. were blown from a piece of 
ordinary soft glass essentially in the way illustrated in the preceding 
communication.^ These must be much flattened on both sides to give 
flexibility (necessary on account of the pressure in the bomb), tested 
by pressing with the fingers. The volume of each bulb is easily found 
by immersion, and it is filled essentially in the way previously de- 
scribed. The bulb should not only yield under the pressure, but should 
be thin enough to burst easily. Otherwise the violent explosion might 
lead to incomplete combustion, and to injury to the apparatus. Typi- 
cal very thin bulbs filled with benzene or toluene were found to burst 
with slight explosion at a temperature of about 50° in a water bath — 
a circumstance which may explain the occasional projection out of the 
crucible and incomplete combustion of some of the sugar at first used 
to ignite the liquid. Accordingly, instead of sugar about 0.1 g. of 
paraffin was used for this purpose, melting it upon the inside of the 
mouth of the weighed crucible by a hot glass rod outside of the crucible. 
A weighed fiber (about 0.5 mgm.) of cotton wool was attached to the 
paraffin, while heated for a moment locally by means of the rod applied 
outside of the crucible. A minute coil of very fine platinum wire en- 
veloping the projecting cotton served to ignite it and the paraffin. The 
heat from the burning ring of paraffin ruptured the bulb through the 
expansion of the liquid, and the vapor of the Hquid rose into a ring of 
flame at the mouth of the crucible and was completely burned. This 
method is so easy to adjust and is so convenient that it is a distinct im- 
provement over the method formerly used. The result was of course cor- 
rected for the accurately known heat of combustion of the paraffin and 
shred of cotton wool. 
Method of ignition. — Iron wire, heated by an electric current to start 
the combustion, has several disadvantages. The amount of iron burned 
and the stage of its oxidation are uncertain. Moreover, drops of fused 
oxide are sometimes driven against the platinum, and frequently de- 
stroy the crucible or the lining of the bomb. Very fine platinum wire, 
used by Zubow and Roth, is decidedly better. In detail the method 
used by us was as follows: 7-10 cm. of very fine platinum wire were 
wound in a spiral about 1 mm. in diameter, and attached at the ends 
of two supports directly above the crucible. As already stated, within 
the spiral was placed a weighed shred of filter paper or cotton wool. 
