OF STEAM AT DIFFEEENT TEMPEEATUEES. 
209 
and after the insertion of the globe A, closed by an india-rubber cork. C C is the large 
mercury-bath for heating the glass tube, with its lamp h, and shade of sheet iron Ic : 
the globe A rests on a tripod, n, in the copper bath, and its stem passing down through 
the outer tube, is open at bottom in the mercury-bath. To transfer this globe from 
its place over the basin in which it has been inverted, to form the Torricellian vacuum 
to the boiler, the cap of india-rubber (fig. 9) is placed over the end. A small block of 
wood, X, fixed by a wedge, slides over the outer tube and carries a double-pointed screw, 
by which the level of the mercury in the bottom bath could be read off by the cathe- 
tometer, the length of the screw being added to the height taken from the upper point. 
A frame of wood carried the two thermometers t and t' placed above and below the 
globe in the copper bath. The boiler was heated by gas-jets, E, as before. The 
difficulty arising from the retardation of the passage of heat through the outer glass 
tube, already alluded to, was found in an increased degree in these experiments, owing 
to the small surface exposed to the heat of the mercury-bath. After the ffacture of two 
or three tubes, which from their large size were very imperfectly annealed, an iron 
tube, p, was cemented to the lower part of the glass, and entirely removed the difficulty. 
It enabled a \dolent ebullition to be maintained in the glass tube, if necessary, at more 
than twenty degrees lower temperature in the mercury than before. 
The globes were filled with mercury, inverted, and the water introduced as before. 
Capacity of Glole G. 
Water introduced =18425 grains at 50° Fahe., this reduced to 39°T =18427 grains, 
Graduation : First file mark 
Second file mark . 
Third file mark . 
Fourth file mark . 
Fifth file mark . 
The utmost care was taken throughout the experiments to prevent the admission of 
air or any other influence likely to affect the accuracy of the results. 
= 18427-0 grains. 
= 18553-2 grains, 
= 18679-4 grains. 
= 18805-6 grains. 
= 18931-8 grains. 
2 F 
MDCCCL.X. 
