BY HEAT OP "WATER A]^D MERCUET. 237 



the middle of it to make room for the cylinder a. The wires E, E, as shown in 

 fig. 5, were connected together by a stout wire and binding screws. The draft-pipe b, 

 figs. 5, 6 (of zinc tubing soldered to the one-half of the cover joining at e with b), served 

 to draw off the steam formed at liigh temperatures, thereby preventing its condensation 

 on the platinum wire. This was accomplished by leading the end of the pipe into a 

 chimney and creating a draft by lighting a gas-burner in it. It was found by experi- 

 ments at low temperature that creating this draft had not the slightest influence on the 

 weighings, for those made with and without it were exactly the same. 



In the middle of the box stands the silver cylinder a, filled -with distilled water, and 

 in this the metal or glass was weighed. As seen in the figure, the thermometer-bulb 

 stands in the same level as the metal. To prevent the evaporation of water by the 

 current of air svicked in at e by the draft-pipe, as well as to hinder particles of dust 

 falling into the water, the cylinder was covered with a platinum cover, f, f (divided in 

 two), with two holes, the one for the fine wire, the other for the thermometer*. The 

 water in the box was heated by steam, the pipe surrounding the cylinder, a small screen 

 of sheet zinc bent outwards being placed between them to prevent the steam coming in 

 direct contact with the cylinder. The general method of observing with this apparatus 

 was as follows : — The substance to be experimented on was cast or ground to a form 

 somewhat like fig. 7, and suspended by means of a slip-knot ftiade with the fine platinum 

 wire in the cylinder filled with boiling distilled water. This being made to boil, was 

 boiled with the substance for the space of half an hour. Another silver vessel was 

 kept ready with boiled out and boiling water to supply the loss by evaporation. 

 After boiling for the half hour, the cylinder v,as placed in the box already filled with 

 water of the proper temperature, and the platinum covers placed on it ; the box was 

 then covered with the zinc and wooden covers, of course great care being taken to let 

 the fine wire swing freely. Whilst experimenting at high temperatures, steam had to 

 be passed into the box to keep a constant temperature. By means of a small boiler, 

 heated by gas placed at some distance from the apparatus, this was easily effected. In 

 fact, by carefully regulating the gas, any temperature between 50° and 100° may be 

 kept constant for any time. A waste-pipe was fitted into the side of the box to allow 

 the water when it reached a certain level to fiow away ; as soon as the temperature 

 became constant, the first weighing was proceeded with ; in the one pan of the balance, 

 large weights were placed so as to make that side of the balance the heaviest ; this 

 is brought into equilibrium by placing smaller weights in the other pan, namely, the 

 one to which the platinum wire is fixed. The balance stands in a glass case, and 

 surrounding this is another glass case (not shown in the figure), to keep. the tem- 

 perature of the balance as constant as possible. It did not vary during a series of 

 observations more than 1°. The proper weight having been found, which it was 

 possible to do to an accuracy of 00001 grm. Avhen weighing in water, it was noted, 



* To diminish the amount of air sucked in at c, and as a protection againt dust, the opening at e was covered 

 with a piece of zinc cut as shown in fig. 8, the hole in the centre having about 2 millimetres diameter. 



