Properties of Pure Substances : Nitrogen. 11 



enabling the large glass vessel to be placed in communication 

 either with the external air through H, or with the system of 

 purifying tubes. The large vessel with tap R is filled with 

 copper gauze and strip, and communicates by a tube having 

 a rubber-joint and clip D and tap C with another large 

 vessel placed 2*4 metres above it (measured from bottom to 

 bottom). The upper vessel can be put in communication 

 with a water-pump by a pipe passing through B and having 

 a tap at A. This upper vessel contains strong liquid am- 

 monia. It will be readily understood that by working the 

 taps &c. the ammonia may be drawn into the upper vessel 

 while air is being admitted to the lower, and may then be 

 allowed to descend by gravity, and furnish the requisite head 

 to force the gas through the remainder of the apparatus when 

 the two-way tap F is suitably turned. G is an auxiliary tap 

 for allowing samples of the gas to be drawn off and tested for 

 oxygen in an ordinary Hempel's gas-analysis apparatus, not 

 shown in the diagram. The air, from which the greater part 

 of the oxygen has been absorbed by the copper and ammonia, 

 now passes into a horizontal tube I about half filled with 

 strong sulphuric acid, where the greater portion of the 

 ammonia is absorbed. The management of this tube requires 

 care or the entrance soon gets stopped up by the formation 

 of ammonium sulphate. After two years' work this tube was 

 replaced by a large glass wash-bottle with ground-in stopper. 

 J is a tube containing strong sulphuric acid through which 

 the gas bubbles ; h is merely a drawn-out end for facilitating 

 the blowing-out of the joints of the glass tubes. At K are 

 two " double " wash-bottles containing the chromous chloride 

 syrup; and L represents a U-tube with ground-in tap-stoppers 

 filled with glass beads, and likewise containing chromous 

 chloride. The stoppers of L and K are weighted with lead 

 weights to enable them to stand the pressure, and mercury 

 cups are arranged round the stoppers. M is a tube contain- 

 ing a solution of caustic potash. N contains nitrate of silver 

 together with a little silver Irvdroxide and potassium nitrate, 

 contains more potash, and P contains strong sulphuric 

 acid. Q is half filled with potash in lumps, and half with 

 soda-lime. R is a tube into which phosphorus pentoxide 

 has been distilled so as to present a large surface. S, a Win- 

 chester bottle with ground-in stopper, and the wide tube U 

 both contain phosphorus pentoxide. Originally there was a 

 mercury-gauge at V, and though this was dispensed with, 

 the apparatus for eliminating mercury vapour was allowed 

 to remain because one or two drops of mercury had got into 

 the tube near V. W is a specially fine tap protected with 



