946 
DR. J. JOLT ON THE SPECIFIC HEATS 
(Table IX.) were, however, not so concordant with those recorded in Part I. obtained 
with the lighter vessel then used. This is not to he wondered at when it is 
remembered that a 1 per cent, accuracy in the case of dealing with 4 grammes of gas is 
already a determination closer than one part in 4000 of the total precipitation upon 
the two vessels in the calorimeter, or one two-thousandth part of that upon the vessel 
containing the gas. 
The carbon dioxide used in the experiments was obtained from the brewery of 
Messrs. Guinness and Co. In the brewery it is removed from the fermenting vats, 
from a level low down, some 15 or 20 feet below the edge of the vat, which remains 
filled with the gas. It is then purified by washing with water and treatment with 
permanganate of soda, and compressed into iron bottles. In use it is best to invert 
the bottle somewhat, so as to draw from the liquid. The gas used in the earlier 
experiments had a faint alcoholic smell. Later, gas was supplied to me through the 
kindness of the head engineer, Mr. Geoghegan, which had no perceptible odour. 
Derminations of the amount of impurity were frequently made, by absorption with 
alkaline pyrogallol of some 65 ctib. centims. of the gas over mercury. The impurity 
(air, probably) was in all cases small; at worst, about 1 part in 360 by volume. A 
series of experiments (Table XII.) was carried out upon gas prepared in the laboratory 
from pure bicarbonate of soda, and pumped into the sphere with the aid of the 
mercury pump, described in Part I. This gas contained, according to subsequent 
determination, an impurity of only one part in 1015 by volume. These experiments 
reveal no discrepancy with those made upon the less pure gas. It is, indeed, not to 
be expected that the impurity of one in 360 by volume would produce a perceptible 
error. In filling the gas into the sphere it was passed through an iron drying tube 
about 1 centim. in diameter and 35 centims. in length, filled with asbestos and 
phosphorus pentoxide. It was found that the transfer of the liquid into the sphere 
was greatly facilitated by cooling the latter with ether poured on muslin placed 
around it. 
The first series of experiments were made upon a charge of 10'542 grammes, which 
by determination showed an impurity of 1 in 485 by volume. They are contained 
in the following table, and the succeeding table gives a calorimetric comparison of the 
empty spheres applicable to the experiments. The mode of estimating the pressure, 
obtaining nnd of evaluating the deduction to be made for effects other than that (sr) 
due to the calorific capacity of the gas at constant volume, is given further on, after 
the experiments have been recorded. 
