324 Dr. Eobinson on a New Mercurial Gasometer [June 16, 



One end of the bell's cock communicates with the atmosphere, the other 

 with the receiver-plate R. This is of glass 2 inches in diameter, 0*75 thick, 

 and is cemented on the top of the iron pillar P. Through it are drilled 

 the passages shown in fig. 3 ; in ^ is ground the glass tube, shown in fig. 1 

 by T, the end of which is in contact with the cock, and their junction 

 made air-tight by a tube of Para caoutchouc ; in g and k are similarly 

 ground the siphon-gauge G and the glass cock K. These all communicate 

 with the receiver by the passage v, and by removing the tubes can be 

 easily dried or cleaned. The cock K is connected by elastic tube with the 

 catch-jar N, which is supported in a small mercurial trough M. 



The operation of this machine as an air-pump is as follows : — The re- 

 ceiver being placed on R, open the screw S, press down the plunger nearly 

 to the bottom of the cylinder, remove the key of the bell- cock, and pour 

 through the opening which it leaves as much mercury as will fill the bell 

 to the bore of the cock. In this one 10 lbs. are required. Raise the 

 plunger to the top, and the metal will subside from the bell till only 0*3 of 

 an inch remains on the top of B, filling the space left vacant in D by the 

 rising of the plunger. The length of the plunger and the height of B 

 must be adjusted to this condition. Replace the key ; turn it to commu- 

 nicate with the atmosphere (which position I call («)), and depress the 

 plunger. The mercury will rise again in the bell, filling it, and expelling 

 the air from it, till at last a little mercury will appear in the bore of the 

 cock. To prevent this from being splashed about, a bit of bent tube v is 

 ground on the end of the cock, which receives it, and when it has too 

 much is removed and emptied into D through S. Secondly, turn the key 

 to shut off the bell (position (o)) ; draw up the plunger, close S, open E, 

 and couple it to an air-pump, with which exhaust D. This pump may be 

 of the commonest description, for an exhaustion of one or two inches is 

 quite sufiicient. The mercury will sink in the bell, leaving above it a 

 Torricellian vacuum. Close E, and turn the key to communicate with the 

 receiver (position {r)) ; its air or gas will expand into the bell. 



These three operations form the cycle of operation, and must be re^ 

 peated till the required exhaustion be obtained, with one modification of 

 the first one. In it, at the second and all subsequent strokes, the key is to 

 be at (o) and S opened ; thus the atmospheric pressure will raise the mer- 

 cury and do much of the plunger's work ; that must then be depressed 

 and the key set at {a) ; the other two steps are as at first* 



When the instrument is to be used as a gas-holder, either the feceivef 

 must be in its place, or the opening of R must be closed by a piece of flat 

 glass ; the bell must be filled by the plunger, and made, by (r) and by 

 opening Tc, to communicate with the jar N. The mercury will rise in that 

 to its neck, and sink in A ; fill A again, pass gas into N, and, by carefully 

 working the key, draw it into A till that is full. As this gas will be mixed 

 with the air of the vessels and passages, it must be expelled, and A refilled 

 till its purity is certain. If it be noxious, it must be conducted into some 



