RICHARDS AXD MATHFVVS. — HEAT OF EVAPORATION". 529 



As may have been inferred, many preliminary determinations were 

 made in order to determine the best conditions, and the various dangers 

 to be avoided. Water, having been the liquid most studied by others, 

 ■was chosen as the most desirable substance with which to test the ap- 

 paratus and method. 



Over thirty trials were made with the object of finding the best posi- 

 tion of the vaporizer and testing various devices to prevent radiation. 



Finally the following method of experimentation was adopted : The 

 pan-like copper cover ^^G, Figure 5) of the calorimeter jacket was 

 placed tempcirarily upon a raised stand which permitted easy access to 

 its lower surface : the vaporizer (^V) containing the liquid to be investi- 

 gated was adjusted into its place (j>acking the space X between its 

 silvered envelope and the copper cover with cotton wool\ the empty 

 weighed condenser {A) was then attached to the beak of the vaporizer 

 (B) as it protruded beneath the elevated copper cover, and the ther- 

 mometer and stirrer were arranged in their orifices. Meanwhile the 

 calorimeter had been almost filled with a weighed amount of water at 

 about 20', and the jacketing crude alkaline solutions had been adjusted 

 at exactly the same temperature. When all was ready, the copper 

 cover with the suspended condenser was placed into position over the 

 calorimeter, the condenser being immersed very carefully in the calo- 

 rimeter water. The silvered beak of the vaporizer itself dipped about 

 a centimeter under the surface, as shown in the diagram. The slow 

 backward current of air, which served to prevent the access of vapor 

 to the condenser until all was ready, was then driven through the ap- 

 paratus, and at the same time the heating electrical current was turned 

 on within the vaporizer. When the Kquid was actively boiling, a careful 

 study of the radiation-condnetion-efiect on the calorimeter was made 

 This having been accomplished, the actual experiment could begin : 

 the stopcock {K, Figure -4) above was closed and the backward current 

 of air discontinued. The rapid current of vapor was thus suddenly 

 switched into the condenser, and the temperature of the calorimeter 

 began to rise at a rapid rate. This rate was continuously matched in 

 the environing alkali by admitriug acid in suitable quanriries, and the 

 exjieriment proceeded very smoothly until a rise of about 4 degrees 

 had been accomplished. Finally the stojxxx^k (K. Figure 4^ above the 

 vaporizer was suddenly opened, the posterior outlet 0^', Figure 5 > of the 

 condenser closed, and the electric current cut off. The vapor forming 

 was then firee to es^cape into the air. and when boiling stopped, the 

 condensed liijuid was not drawn back into the vaporizer by the sudden 

 vacuum formed upon cessation of boiling. For at least five minutes 

 afterwards, the temperature of the calorimeter was read every minute 



VOL. XLVI. — 34 



