842 Mr Kemp's Description of' an Improved Blompipe. 



The instrument may be rendered more perfect, by having a 

 stop-cock placed in the tube C, to regulate the current of air ; for 

 most purposes, however, this is unnecessary. 



Instead of the tube D d being terminated in E Cy it might 

 have been continued to the bottom of the vessel, and be there 

 terminated in a portion of mercury. This construction would 

 answer equally well, if the instrument was to remain stationary ; 

 but, during motion, it sometimes happens that the mercury is 

 removed fjom the bottom of the tube, and the elasticity of the 

 air acting on that column of mercury within the tube, forces it 

 out at the orifice D. 



The same principle of constructing a valve may be apphed to 

 the hydraulic blowpipe. The tube coming from the bellpws, 

 instead of having a common valve inserted into it, and termi- 

 nating at the top of the air-vessel, may be continued to the bot- 

 tom of it ; when, upon the air being forced in by the bellows, 

 it displaces the water from the tube, and rises into the upper 

 part of the air-vessel. The water now acts as a valve, and pre- 

 vents the return of the air by that tube, while it is forced out 

 by the otiier tube in the usual manner. 



By this plan we obtain a valve of the most simple de- 

 scription, and without the possibility of getting wrong ; nor is 

 there a greater pressure required for forcing in the air by this 

 method, than when the tube terminates at the top of the air-ves- 

 sel through a common valve. 



2. Ascent and Combination of Mercury on Metallic Wires. 



While making some experiments with the liquid amalgam of 

 mercury and zinc, upon the other metals, the following singular 

 fact came under my observation. 



Having dissolved a quantity of zinc (about a 30th or a 50th 

 part) in a portion of mercury, I poured part of it into a tall 

 glass-jar, and filled the remainder of it with a strong solution of 

 muriatic acid and water. I then placed clear metallic wires 

 perpendicularly in the jar, so that their extremities might dip 

 into the amalgam ; the moment they came in contact with it, hy- 

 drogen was evolved in great abundance from them. The mcr- 



