630 SEC. 13. CHEMISTRY. 



IV. APPARATUS IN GENERAL USE IN LABORA- 



TORIE. 



2525. Apparatus for regulating the Pressure of Gas. 



Prof. A. Crum Brown. 



The apparatus consists of a gasometer, the pressure of the gas in which 

 depends upon the weight of the inverted vessel and that of the counterpoises. 

 The peculiarity of the arrangement lies in the mode in which the gas is intro- 

 duced into the gasometer. The gas is led from the main or meter to a fixed 

 vertical tube, and thence by a short piece of india-rubber tube to a metal 

 tube fixed to one of the counterpoising weights, and from that tube to the 

 gasometer. When the pressure in the main increases the vessel rises, and the 

 counterpoise falls ; the short india-rubber tube is thus bent, and the entrance 

 of gas into the gasometer hindered. This short india rubber tube is thus a 

 self-acting valve, always admitting exactly the same quantity of gas as is 

 drawn off from the gasometer, and as the motion of the gasometer is very small, 

 the pressure is practically constant. 



2524a. Oxygen Generator. Jo fin Craig. 



The gas (generated from chlorate of potash and manganese, in equal quan- 

 tities) passes from the retort C to the bottom of the gas holder B (which is filled 

 with water) by the tube F. The water is displaced through the tube II into the 

 reservoir A until the pressure has been reached for which the lever Q has 

 been loaded. When that point has been reached, the pressure acting on the 

 bellows K raises the lever Q, and so diminishing the source of heat ; the other 

 end of the lever regulating the air to the amouut of gas admitted to the 

 Bunsen burner. (By changing the fulcrum of the lever to U the sliding tube is 

 reversed in its action, and adapted for diminishing the flame of a spirit or 

 other lamp where gas is not available.) When the pressure is again reduced 

 below the required limit, the lever, falls, opens the stop-cock O, and more gas 

 is generated. The object of the second retort is that the one may be 

 re-charged while the other is in use, thereby securing continuous action. A 

 convenient working pressure is found with 3 inches of water in the reservoir. 

 The regulator J controls the pressure of gas through the exit pipe I, fulfilling 

 the same office as the regulator in the hydrogen generator. By this means 

 both the production and working pressure of the gas is regulated. 



The advantayes of the combined apparatus are, 1st, a continuous or 

 intermittent supply of oxygen and hydrogen gases may be obtained in any 

 quantity and at any pressure, as the rate of production depends solely on the 

 rate at which the gases are consumed ; 2nd, being self-acting, little super- 

 intendence is required ; 3rd, great economy (as compared with the use of 

 bags), all the gas made being available ; 4th, danger from explosion is reduced 

 to a minimum (a.) from the small quantity of gas in stock, and (6.) undue 

 tampering with the levers would only result in bursting the cloth bellows of the 

 regulator. 



At G there is a small valve, which remains shu' until the heat is withdrawn 

 from the retort ; when, to prevent the water rising to fill the partial vacuum 

 from condensation in the retort, communication is at once established by the 

 valve rising and allowing gas to restore the equilibrium. 



The apparatus is suitable for lighthouses, signal lights, whips' lights, &c. 



The three copper tubes are adopted to the hydrogen generator, the three 

 brass tubes to oxygen. 



2524b. Hydrogen Generator. John Craig 



To generate the gas pieces of zinc are placed in the lower vessel at E. 

 Dilute acid, added to the upper vessel A, comes in contact with the zinc 



