Liquefaction of Hydrogen. 415. 



whence it can return through w and H and the cock i to the 

 main supply-pipe N. The liquid which separates from the 

 gas is ultimately collected in the vacuum-vessel K, which can 

 easily be removed. 



In constructing the apparatus the coil D was wound on 

 the thin steel tube c which contains the valve-rod. The latter 

 is screwed at its lower end into a perforated brass cylinder, 

 soldered to the end of c, enclosing the expansion-jet. By 

 turning the milled head a. the width of the annular space 

 between the jet and the end of the valve-rod can be accurately 

 adjusted and the flow of gas controlled. This valve was made 

 for me by Brings Oxygen Company after the pattern of Dr. 

 Hampson, who first applied it in his apparatus for liquefying 

 air. To the use of this form of valve I must attribute the 

 success of the work, for, unlike the pinhole-valve, it does not 

 become blocked with the impurities which separate from 

 hydrogen obtained by treating commercial zinc with sul- 

 phuric acid. The coil itself consists of 80 feet of solid drawn 

 copper tube o£ -fa inch internal and -^ in. external diameter ; 

 in winding it the spirals ran alternately away from and 

 towards the central tube, and great care was taken to pre- 

 serve a uniform external diameter of 2| inches. The coils 

 were carefully spaced and fixed in position with solder as 

 each layer was wound. 



The length of the regenerator-coil D was 7 inches; and it 

 must be pointed out here that in absence of all quantitative 

 knowledge as to the behaviour of hydrogen at low tempera- 

 tures, the choice of this dimension was a matter of guess- 

 work ; it w r as found, however, to be sufficient. 



The next step in the construction of the apparatus was to 

 fix the flanged plates d and e, which form the top and bottom 

 of the chamber B, onto the tube c. The coil passes through 

 both these plates, and e is also pierced for the passage of the 

 exhaust-pipe /and for the liquid-air valve which is controlled 

 by the rod h ; the latter is screwed through a block fixed to 

 the upper surface of e, so that by turning c the conical point 

 closes to a greater or less extent the hole in the plate. All 

 these junctions were made with bard solder ; the tube g y 

 which fits exactly over d and e, was then fixed in position 

 with soft solder. 



To allow of the escape of the hydrogen gas after its passage 

 through the coils, a brass tube k of the same external diameter 

 as the coil was fitted at the top to g by means of a collar 

 soldered to both tubes, and supported by distance-pieces at 

 the bottom. The annular space F so formed communicates 

 with the escape-pipe Gr, as shown in the figure and section ; 



