HEAT OF EVAPORATION OF WATER. 279 
have taken place into and out of the annular space between the tube and 
thermometer stem, according as the calorimeter was warmer or cooler than the 
tank water. This thermometer had also to be frequently removed in order to 
insert liquids into the flask, and therefore any junction at the bottom could not 
be made a permanent one. The difficulty was surmounted as follows :--The 
silver tube & (Plate 5, fig. 1), which passed up from the lid of the silver flask 
was soldered to the calorimeter lid, above which it projected. A hollow brass rod 
just fitting the glass tube, but with its lower end tapered, was, before fixing the glass 
in place, held vertically with the tapering end filling the open end of the silver tube. 
The annular space between the silver and surrounding brass tube was then filled 
with the melted alloy, to above the top of the silver, and the glass tube lowered into 
its final position. When the alloy hardened, the brass rod was loosened by lowering 
into it a red-hot wire. The lower inch or so of the brass rod having been cut off was 
then placed co-axially round the thermometer stem and made one with it by filling 
the annular space between it and the stem with the same invaluable alloy. Thus, on 
lowering the thermometer into its place, the brass tube almost exactly fitted into the 
ring of alloy at the bottom of the glass tube. The fit was made good by prolonged 
grinding with rotten stone—using the thermometer stem as a rotating shaft. The 
result was a practically air-tight join at the calorimeter lid. It must be remembered 
that as the air-tightness was secured by the cork at the upper end, this joint had not 
to stand any pressure, but was only required to prevent diffusion. 
I have, for two reasons, fully described this method of fixing the tube. (1) I 
thereby overcame a difficulty which had perplexed me for a long time; (2) it was 
necessary to explain the constriction at the lower end of the tube h, which im its turn 
became a source of difficulty when I altered my method of experiment. 
J and /, (fig. 3) are the insulating junctions for the rack on which the coil 
was. wound. 
The base of the calorimeter, which was not fixed until everything else was in 
place, was heated until solder contained in the circular trough, of which a section is 
snown at M (fig. 1), became fluid; the calorimeter was then pressed down upon it, 
and, as soon as the solder commenced to harden, the calorimeter was set in cold 
water. The base was thus soldered on without melting the alloy in the lid or 
injuring the internal fittings. 
The whole apparatus was a difficult and complicated one to construct, and I ewe 
my sincere thanks to Mr. Tuomas for the ingenuity and patience he devoted to the 
task. My brief description can convey but little idea of the many difficulties that 
had to be surmounted between the conception and completion of this apparatus, and 
I may mention that although commenced in February, 1893, it was not until the 
spring of this year (1894) that the calorimeter could be regarded as completed. 
