50 Dr. J. A. Harker on 



simultaneously to the heat of the steam within, and to external 

 cooling by the calorimeter water. Accordingly a washer of 

 thin sheet rubber, with the necessary holes for the screws, 

 was first moistened on both sides with a solution of pure 

 india-rubber in vaseline, and placed between the surfaces. 

 This formed an excellent joint, which never failed in a single 

 experiment, the condenser being at the same time easily 

 detachable for weighing. In order to prevent the crushing 

 of the rubber ring from closing the passage for the steam, 

 a very short tube H was soldered to the calorimeter 

 projecting downwards and inwards about 3 or 4 mm. 

 into the condenser tube. It will be seen that from the 

 highest point of the two inclined tubes the slope is such, 

 that whatever steam condenses in metal reaches the 

 condenser, and that condensing in ebonite flows back, 

 lodging at the bottom of the tube. As a drop of water 

 always remained hanging on the tube H, this was dried 

 in each experiment after removing the condenser by a 

 piece of weighed filter paper, and the increase in weight 

 added to that of the water in the condenser. 



The steam jacket reached as far as a collar turned on 

 the ebonite tube C D, and before every experiment this 

 jacket was heated to a few degrees above ioo°, so as more 

 quickly to bring the parts within it to that temperature. 

 It was found that when the lead coil was not directly in 

 contact with the pipes round which it was wound, and 

 steam at no° had been passing through it for half an hour, 

 no appreciable superheating could be detected in a current 

 of steam passed through the central tube (about 50 cm. 

 long) even at a very slow rate. Hence it was thought 

 advisable to minimise all risk of condensation on the walls 

 of the steam tube proper, by maintaining the jacket always 

 above ioo°. As the coil of lead was of considerable length, 

 and its small bore offered a fair resistance to the passage 

 of the steam, its temperature varied slightly from end to 



