418 Dr. M. W. Travers on the 



The tube / communicates with an exhaust-pump which is 

 not shown in either figure. It is a simple double-action pump 

 with a single cylinder of 3-inch bore and 6-inch stroke, 

 and, driven by a half-horse-power gas-engine, maintains a 

 vacuum of 100 mm. of mercury in the chamber C. The 

 barrel and plug of the stopcock t are bored so that C can be 

 cut off from the pump and opened to the air ; through the 

 stopcock v the pipe G can be placed in communication with 

 the pump. 



It is now convenient to call attention to the general system 

 of heat-insulation in the apparatus. The coil A is surrounded 

 with solid carbonic acid and alcohol, contained in an earthen- 

 ware battery -jar which is unprotected ; the tube between A 

 and B is surrounded with a wrapping of animal wool and 

 covered with baize. B and C are protected by the cold gas 

 returning through the annular space F after passing through 

 the regenerator-coil D ; additional protection is afforded by 

 the layer of animal wool inside the cylinder Q. The 

 increasing steepness of the temperature-gradient at G is 

 compensated for by the protecting influence of the upper part 

 of the vacuum-vessel H ; the vacuum-vessel M, which contains 

 liquid air, serves as a protection to K and the lower part of the 

 regenerator-coil D ; it also prevents deposition of moisture on 

 the tube L. The method of supporting the apparatus by the 

 tube m answers admirably, for as the space between m and k 

 is packed with wool, the gland p only becomes frosted over 

 when the experiment is at an end, showing that the influx of 

 heat in this direction is inconsiderable. 



The hydrogen gas was obtained by the action of dilute 

 sulphuric acid on commercial granulated zinc, and was stored 

 in a gasometer over water. The gasometer consists of a 

 cylinder of sheet iron (No. 16 gauge), 6 feet in height and 

 5 feet 6 inches in diameter, inverted in a cylindrical tank 

 which was filled with water. The gas enters and escapes 

 through a 2-inch iron pipe, passing through the bottom of 

 the tank and terminating inside a small dome 6 inches in 

 diameter on top of the inner cylinder. This arrangement 

 makes it possible to expel the whole of the gas from the 

 gasometer without danger of introducing- water into the 

 supply-pipe. Before filling the gasometer the water in the 

 tank is saturated with hydrogen by passing a stream of the 

 gas through a tube reaching to the bottom. This operation 

 occupies about five days. 



The main bulk of the hydrogen is generated in the following 

 manner. About 40 lb. of zinc are placed in a beer-cask fitted 

 with a tap-funnel, a delivery -tube, and an escape-pipe, which 



