specific and Latent Heat of Vaporisation. 3 



DESCRIPTION OF APPARATUS. 



The final apparatus used was constructed as follows : AA 

 (Fig. i) is a cylinder of sheet brass, seven centimeters in 

 diameter and twenty-two in height. At the bottom of this 

 is soldered the ring D, turned out of sheet brass, to which 

 a cone of thin brass is fixed, carrying the tubulure L, the 

 small pipes G, and the inner cylinder of thin brass BB. At 

 the top of A is soldered the lower one of two flat rings of 

 brass C, which are ground together and held in contact by 

 means of a bayonet joint. To the upper of these rings is 

 soldered a brass cone bearing the tubulures N and O. To 

 the ring D are soldered three brass ears E, to which the 

 wooden pillars F are screwed. These are fixed to the round 

 wooden base H provided with levelling-screws K. 



The tubulure O is filled with plaster of paris, through 

 which a vertical hole of about two millimeters' diameter is 

 bored. A fine platinum wire, suspended from a lead counter- 

 poise, which takes the place of one scale-pan of a balance, 

 passes through this hole and carries at its lower end the 

 body to be experimented on. Under this hangs a small cup 

 of platinum or brass to collect the condensed liquid. In 

 some cases two of these are used, one underneath the other, 

 to catch any possible droppings. 



The instrument in this form is not quite as convenient as 

 the second one described by Joly, but its construction is 

 much easier, and it is probably lighter, and therefore more 

 quickly heated by the steam. It is much higher than is 

 necessary for ordinary purposes, having been designed for a 

 special use. If the cylinder A were half its actual length, 

 the apparatus would be much more compact and would 

 probably work better. 



Figure 3 shows the complete apparatus with arrangements 

 for passing any desired quantity of vapor through the calor- 

 imeter and returning the condensed vapor to the boiler. 



From the boiler F the vapor passes to the tap B, the 

 construction of which is shown in Figure 2. It consists 



197 



