OF GASES AT CONSTANT VOLUME. 
963 
outwards to confer stiflihess), with corresponding flanges, can tightly close the inner 
and outer chambers. To make a joint impervious to the vapour in the space between 
the chambers it was found requisite to lay on a flat rubber ring with rubber cement 
and compress these between the flanges by five screw-clamps placed equidistantly 
around each joint. In the case of the use of ether a lutant had to be used 
instead of the rubber. After many trials it was found that one made of whiten¬ 
ing and glycerine mixed to a stiff consistency gave the best results, glycerine 
being almost insoluble in ether. In the upper side of the inner drum, over each 
sphere, a wide opening closed by a light conical roof of brass is provided. One is 
partially seen in the illustration. This cone is prolonged by a tube about 1 cm. in 
diameter, which finally emerges through the top of the outer drum. . Here it is ground 
to a smooth horizontal edge and fitted with the loose adjustable cone and self-adjust¬ 
ing disk, which permits the free passage upwards of the wire through a very fine 
opening, as described in the ‘ Proc. Boy. Soc.,’ loc. cit. The edges of the wide 
openings in the roof of the inner drum are turned a little upwards all around 
into the cone, so that water drops, running down the latter, will not fall off 
upon the spheres, but be conducted, as by a gutter, to the lowest point of the 
intersection of the cone with the cylinder and then overflow harmlessly down the 
wall of the drum. 
Steam is admitted into the inner chamber by a wide central orifice 3*5 cm. in 
diameter at the back of the drum, the steam-pipe being arranged as described in 
the ‘Proc. Roy. Soc.,’ loc. cit., and concealed from view in the figure by the wooden 
stand which supports the instrument. The escape of the air replaced by the steam 
takes place through a central opening (1'7 cm. diameter) at the bottom of the 
drum, a tube leading it directly outside the calorimeter. When the air has been 
expelled and steam is seen to follow it, the opening is narrowed by insertion of a 
cork carrying a brass tube, shown in the figure, of about 8 mm. bore. This is 
bent and can be turned outwards, or to one side, to direct away from the balance 
the continuous outflow, necessary to preserve the slow circulation of steam in the calo¬ 
rimeter. A third central tubulure entering the inner chamber enables a thermometer 
to be inserted, as shown. 
The outer drum has four tubular openings; two below (one at each end) to 
permit an inflow of the vapour from the boiler attached beneath it, two above to 
convey the excess of vapour to the condenser which is seen standing behind the 
balance. This condenser is simply a tin plate cylinder, open at top with a central 
inner cylinder of thin copper also open at top, and seen rising a little above the level 
of the outer cylinder. Ice is placed in the annular space between during experiment. 
The leading tubes are of sUch width and so sloped that the returning current of 
condensed vapour will not choke the tubes, but flow freely back into the vapour 
jacket and boiler beneath. It is important that these conducting tubes should be of 
glass so that the heating of the boiler can be adjusted to })roduce the least current 
6 G 2 
