Hydro-oxygen Blowpipe. 43 



The valve at the end of the rod, attached to the lever, L, being 

 kept shut by the catch, M, the screw plug, H, removed, the acid 

 is introduced through the aperture thus opened. In the next 

 place, the plug being replaced, and the valve depressed by means 

 of the lever and rod, so as no longer to close the opening, which 

 it had occupied, the acid descends from the chamber into the cav- 

 ity of the vessel beneath it. The valve is of course restored to 

 its previous position as soon as the acid has effected its descent. 



The lowermost vessel is furnished with a perforated copper 

 tray, supported by a copper sliding rod, in a way quite analogous 

 to that already described in the case of the copper reservoir. It 

 is also supplied with zinc and its solvent in like manner, being 

 made half full of the diluted sulphuric acid. Of course, on con- 

 tact being produced between the zinc and its solvent, the gene- 

 ration of hydrogen will take place. So long as the communica- 

 tion between the upper portions of the two vessels is open, the 

 gas will extend itself into both, occupying the whole of the up- 

 per vessel, and that half of the lower one which is unoccupied 

 by the liquid, But if, in this way, the pressure reaches to two 

 atmospheres, as indicated by the gauge,* on shutting the commu- 

 nication through the pipe, B, the pressure in the inferior vessel 

 will augment, that in the superior vessel remaining as before, but 

 the liquid will consequently begin to pass out of the inferior ves- 

 sel through the pipe A, and thus may lessen the contact between 

 the acid and zinc, and finally suspend it altogether. Meanwhile 



the gas in the upper vessel being condensed to nearly half its 



previous bulk, the pressure will be nearly four atmospheres. It 

 will, in fact, always be nearly double that which existed before 

 the pipe, B, was closed. 



In order that nearly the whole of the acid shall be expelled 

 from the inferior vessel, the tray must be depressed till it touches 



the bottom of that vessel. 



The pressure being four atmospheres at commencement, as 

 soon as, by means of a pipe attached to the valve-cock, N, an 

 escape of gas is allowed, the acid is forced again upon the zinc, 

 and thus prevents a decline of pressure to any extent sufficient 



to interfere with the process. 



The gases may be used from a receiver in which they exist, 



in due proportion, safely by the following means : — 



Two safety tubes are to be made, not by Hemming s process 



exactly, but as follows: f . . / A 



A copper tube, silver soldered, of which the metal is about the 

 eighth of an inch in thickness, is stuffed with the finest copper 

 wire, great care being taken to have the filaments straight and 



^ — — — ■ — ^^^— - »■ w_j^^__m e ^ ^— — — - - " ^ m ' ' " " — ^ — «^ ^m^am 



I have used for a gauge an instrument like G, fig- 5, the lube being about two 

 feet in length, and sealed at the upper end. 



