efi^ New Mercurial Air Pufrip. 



unites and forms nitrous acid. The produ£lion of ammonia at the filver wire can be 

 explained on either hypothefis ; but wc fliall take another opportunity of examining this 

 part of the fubje£l. 



The new apparatus which I defcribed In a former paper, feems to anfwer better than 

 was at firft expe£ted ; it has now been in ufe occafionally for a month, and whenever a 

 frelh folution of fait, or muriate of ammonia, is introduced, it appears to be fully a» 

 ftrong as at firft. The addition of a very fmall proportion of nitrous or muriatic acid to 

 the folution of common fait, adds confiderably to its efficacy. 



^ V. 



Defcription of a Mercurial Air Pump ; and of a Double-barreled Air Pump. By RiCBARD 

 Augustus Clare, Surgeon, Jamaica. Communicated by the Author. 



J? IG. 1, PI. XL reprefents a feftion of the different parts of the pump ; A, a large iron 

 tube (being the barrel of the pump) B a fmaller ditto. Thefe tubes are flanched to the 

 iron ftep C. This ftep has a perforation in it, making a communication between the bot- 

 toms of the tubes. The tube B is furmounted by a plate of iron, on which is flanched 

 the iron hemifphere D. The hemifphere has a hole at top, one-tenth of an inch in 

 diameter, with a cap valve and bafon at E. A pipe, b b, of iron or glafs, is inferted through 

 the upper part of the hemifphere, and reaches within a little of the iron plate on which it is 

 flanched. The pipe b b rifes about thirty-five inches above the level of the bafon E ; it is re- 

 verted at top, and defcends to be Inferted into the upper part of the piece G, which has a flop 

 cock at c, leading to the receiver. To the lower part of the piece G, the long barometer 

 gauge d is attached, the lower end of which defcends into the bafon of mercury e, F is a 

 cylindrical piece of light wood (which I fhall call the pifton) made to Aide eafy in the hollow 

 cylinder A. There is a fmall fcrew at a, to draw off the mercury when required. The 

 valve at E is made of a thin iron hoop about three-fourths of an inch long, and half an 

 inch in diameter i the lower end of this hoop is covered with a piece of bladder in the 

 manner of a drum. The valve fits loofely into the cap, which has three grooves on the 

 infide, made in a perpendicular direftion from bottom to top. The ufe of thefe grooves is 

 to allow the mercury to rife freely by the fides of the valve hoop. The ufe of the bafon is 

 only to contain the fuperflous mercury. To try the power of this pump, let the pillon 

 be pufhed down to the bottom of the cylinder, and retained there, as it will have a ten- 

 dency to rife when the mercury is poured in. Take the valve out of the cap at E, and 

 pour mercury into the bafon till it rifes as high as the top of the cap, then thrufl: down 

 the valve, till the mercury runs over the top of its hoop and fills it. The fpecific gravity 

 «f the hoop fo filled will be little lefs than that of mercury itfelf. Let the pifton be now 



drawn 



