

ast 
— ; 
IMPROVED FORMS OF BOMB CALORIMETER. 205 
While this lining has proved very satisfactory not only here, 
but in several other laboratories as well, the expense of the 
platinum is still an objection, and numerous attempts have 
been made to find a cheaper substitute. The attempt of Berthe- 
lot* to electroplate the inside surface with gold did not give 
satisfactory results. Prof. H. W. Wiley, who has used the 
apparatus here described, and has published a method for 
determining the hydrothermal equivalent,t has also made 
experiments with a plating of gold, but it has not proven sat- 
isfactory when plated, either directly on the steel or with an 
intervening layer of copper. There are apparently two diffi- 
culties with the plated lining, one is that it is somewhat porous 
even when carefully burnished, and the oxygen under heavy 
pressure penetrates to the steel. Another is the unequal 
expansion of the thin lining and the thicker wall of steel when 
the interior is suddenly heated by combustion. 
The use of a thin, gold-plated cup of copper, or other metal, is 
under consideration, but we have not yet put it to a practical 
test. We have, however, made attempts to use cups of alumi- 
num spun from sheets of the purest metal we could obtain, but 
have met the difficulty that the aluminum is attacked by nitric 
acid, the amount dissolved being sufficient to interfere with the 
accuracy of the determinations. That aluminum was dissolved 
in appreciable quantities was shown by loss in weight of the cup. 
It is perhaps possible that an enamel may be found which 
will stand the strain of heating and expansion. This would 
solve the rather perplexing problem of an inexpensive lining. 
THE CALORIMETER CYLINDERS.—THERMOMETRIC APPARATUS. 
The bomb when ready for a combustion is immersed in water 
contained in a metal cylinder. This cylinder is surrouunded 
by concentric cylinders or pails of ‘‘indurated fiber,’’ leaving 
air spaces to prevent undue passage of heat between the water 
and the outer air. ‘The arrangement is shown in Fig. 4. The 
cylinder is of britannia metal 12 cm. in diameter, 22 cm. high, 
and holding, with the bomb, not far from 1,700 grams of water. 
A stirrer (SS) moved by a small motor or other agency, keeps 
the water in motion and insures the mixing needed for equal- 
izing its temperature. The calorimeter cylinder stands on 

* Ann. Chim. Phys. (5), 23, 161. + Jour. Am. Chem. Soc., Vol. XIX., p. 439. 
