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Mr. J. Joly. 



fitted together. To enable it to be levelled, it is supported on two 

 levelling screws in front and a centrally placed foot at the back. To 

 afford more vertical room, the base board is cut out centrally in front. 

 The carrier for supporting the substance within the calorimeter is 

 shown in position within the calorimeter. It is made of silver wire, 

 about 0*5 mm. in diameter. The catchwater is of thin platinum- foil, 

 and is removable for drying and cleaning. It is, in fact, supported 

 on a projecting claw beneath the ring of the carrier. Across this 

 ring fine platinum wire is stretched, forming a platform on which the 

 substance may be laid. Four . wires crossing at the centre will in 

 general be sufficient. When resting on these the substance is exposed 

 to the steam on all sides. The total weight of the carrier is just 

 3 grams. It condenses about - 031 gram through a range of 90° C. 



The claw supporting the catchwater performs a double function. 

 In the case of a smooth body, which is also a good conductor of heat 

 and of large thermal capacity, such as a thin vessel filled with water, 

 the precipitation is so copious and sudden that it reaches the catch- 

 water before it attains steam temperature. The result is a secondary 

 precipitation on the outside of the catchwater. This might be in 

 some cases so plentiful as to drop from the bottom of the catchwater, 

 and so be lost. The claw serves to entangle this, retaining it on the 

 balance. 



It is important that an ample supply of steam should flow into 

 the calorimeter on connecting it to the boiler. To make certain 

 of this, a strong gas-burner and a large boiler should be used. The 

 supply, indeed, should be considerably in excess of what passes up 

 the connecting-tube. If this is not so there is risk of air entering 

 the boiler on first coupling it with the calorimeter, which, mixing 

 with the steam, causes a mist of the cooled vapour to flow up the 

 tube. The danger of this is considerable, as there is a strong 

 tendency to an indraught at the boiler, owing to the buoyancy of the 

 water-gas in the ascending tube. In some experiments on the value 

 of the radiation effect, before alluded to, this came strikingly to my 

 notice. The boiler was fitted with a pressure-relief arrangement, 

 consisting simply of a tube taken externally from tbe top of the 

 boiler, bent twice at right angles and brought downwards, so that it 

 opened at a level below the bottom of the boiler. Thus a certain 

 small pressure of steam in this was necessary to drive the buoyant 

 gas down this escape-pipe. 



Hence I concluded that the continued appearance of steam 

 escaping at the relief -pipe was a sufficient indication of an excess of 

 internal pressure. However, in my experiments a large and unaccount- 

 able increment to the weight of precipitation on the substance pre- 

 vailed, and this I traced after much trouble to the entry of air at the 

 relief-pipe. There was, in fact, a circulation of air and steam within 



