Temperature on the Specific Heat of Aniline, 51 



calorimeter and the steel chamber at nearly equal tempera- 

 tures, and it did not, therefore, appear so necessary to guard 

 against convection and radiation gains and losses. Previous 

 experience had convinced me of the absolute necessity for 

 keeping this intramural space dry, for I found that the 

 slightest moisture in the contained air has the most astonish- 

 ing effect in changing the conditions. It was therefore 

 necessary that all joins should be absolutely tight, for the lid 

 of the steel chamber was under water, and I proposed, in the 

 preliminary experiments, to place water within the calori- 

 meter. The use of indiarubber was forbidden, as I intended 

 to insert ether in the silver flask and aniline in the calori- 

 meter ; and even if such had not been the case, indiarubber 

 connexions are, at the best, unsatisfactory and unreliable. 

 I decided, therefore, not to commence my experiments until 

 I found that the apparatus was absolutely gas-tight in all 

 parts ; and I may mention that the greater part of last summer 

 was unsuccessfully devoted to the endeavour to secure per- 

 fection in this respect. During last winter I spent considerable 

 time in the effort to obtain some suitable medium by which 

 to join glass to metal ; and with the assistance of Mr. Thomas 

 I was at last successful in procuring an alloy by which an 

 air-tight join could be formed*, and which would stand con- 

 siderable changes of temperature. Five glass tubes passed 

 from the calorimeter to the steel lid, rendering ten such glass- 

 to- metal joins necessary, besides several similar ones in the 

 exterior connexions. 



In the spring of this year the intramural space was ex- 

 hausted 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 for a 

 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 readmitted to this 

 space, and the silver flask with its connected 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 diffi- 

 culty had been surmounted. 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. 



I now pass to a description of that vital part of any such 



* Proc. Camb. Phil. Soc. 1894. 

 E2 



