278 MR. E. H. GRIFFITHS ON THE LATENT 
thus all contact between the leads and tank-water was prevented. The calori- 
meter was hung below the steel lid by five glass tubes, thus ten air-tight junctions 
of glass to metal were required, in fact, four of these junctions were, in reality, 
double ones, for the lower extremities of the narrow tubes e and f (Plate 5, fig. 1) 
had not only to be fixed into the lid of the calorimeter, but also joined on to the 
ends of the silver tubing. In like manner, where they passed through the steel 
lid, they had to join also on to glass tubes leading to two glass taps immersed in 
the outer tank. There were, therefore, practically fourteen such joints. I have 
previously described an alloy by which I was enabled to make these joints absolutely 
air-tight.* In order to show how carefully all these joints were tested, as well as 
several others in the external connections by which communication with the mercury 
pumps was established, I extract the following from Paper A. :—‘‘In the spring of 
this year the intra-mural space was exhausted until the reading of the McLeod gauge 
connected therewith was reduced to 11, indicating a pressure of about 0°12 millim, 
The apparatus was then left untouched fora month, except that the temperature was 
occasionally raised or lowered, and at the end of that time the reading of the gauge 
was still less than 12. Dry air was then re-admitted to this space, and the silver 
flask, with its connecting tubes (embracing about 50 feet of tubing with several joins), 
tested in a similar manner. Those who have had to deal with low pressures will 
understand that, when all was found satisfactory, a great difficulty had been sur- 
mounted. I did not retain this vacuum during the experiments, as I felt that it 
would subject the glass tubes, &c., to a continuous strain which the conditions of the 
experiments rendered unnecessary. The labour had not been lost, however, for I was 
able to count with confidence on the gas-tightness of the whole apparatus.” 
Where the supporting glass tubes entered the calorimeter lid (as shown by the 
plan, Plate 5, fig. 3), they were surrounded by metal tubes (shown by the outer ring” 
in each case) nearly 1 centim. in length which had their lower extremities soldered to 
the lid. The annular space between these and the glass tubes was filled with the 
alloy and the joints on the top of the steel lid, from which the apparatus hung, were 
of the same kind but slightly deeper. The tube 8 surrounded the stirrer shaft. The 
platinum thermometer AB passed down T, and this tube was also used for inserting 
or withdrawing the calorimeter liquid. The thermometer was wrapped with india- 
rubber tape so that the annular space between it and the glass tube T was made 
air-tight throughout the upper 4 inches. 
Through h’ h communication was established between the exterior and the 
silver flask. During my earlier experiments a thermometer stood in this tube 
with its bulb nearly at the bottom of the fiask. It was of course possible to 
render air-tight the connection between the thermometer stem and the top of 
the tube h’, where the latter projected above the tank. This would not, however, 
have been sufficient, for the flask contained a volatile liquid, and distillation would 
* ‘Cambridge Phil. Soc. Proc.,’ 1893. 
