Experiments on the Latent Heat of Steam. 45 



Fig. 2. 

 downwards through CB into the con- 

 densing worm W. At F a side tube is con- 

 nected with a condenser, if desirable, by 

 means of an indiarubber tube fitted with 

 a clip. The tube at F is kept open during 

 the preliminary period ; it is shut just 

 after C is opened, and opened again 

 just before C is closed, so that at no 

 period does the internal pressure exceed 

 that of the atmosphere. The end B of 

 the tube BC is ground into the upper 

 end of the condensing worm, of which 

 the construction differs slightly from 

 that of Berthelot. The steam in our 

 apparatus enters the condensing worm 

 by the straight portion, and not by the 

 spiral. We found this alteration neces- 

 sary as, after the closing of the valve, the 

 air entering the worm tends otherwise 

 to drive the condensed water back into 

 BC. 



The lower half of A was surrounded by a piece of copper 

 gauze bound on with asbestos string, and the lower portion 

 of the tube BC was surrounded in Expts. I., II., III. by 

 asbestos, and in IV. and V. by a leaden steam-coil wrapped 

 closely round it. 



The boiler was heated by a small ring burner, of which 

 the flame was kept at a perfectly constant height from the 

 moment of lighting till it was extinguished. The gas was 

 passed first through a Moitessier glycerine regulator (which 

 maintains the pressure constant to within a half millimetre 

 of water), and then through a tap fitted with a long handle 

 moving in front of a graduated circle. 



These precautions are necessary for accurate measure- 

 ments, as variations in the height of the flame naturally 



