58 Prof. J. P. Cooke on Lecture Experiments, 



Ammonia. — The points to be illustrated in the case of ammo- 

 nia are indicated by the equation 



riTiT h! + [n = h 3 n 



We demonstrate the composition of ammonia by the old 

 methods, which are familiar to every teacher, synthetically by 

 passing a mixture of nitric oxide and hydrogen over heated 

 platinum- sponge as in the beautiful experiment of the late Dr. 

 Hare, and analytically by decomposing aqua ammonise either by 

 electrolysis or by means of chlorine. For the electrolysis of 

 ammonia the decomposing-cell (fig. 1) may be used, filling it 

 with the strongest aqua ammonise and adding a not too small 

 amount of sulphate of ammonia in order to increase the conduct- 

 ing-power of the liquid. The reaction is less simple than in the 

 electrolysis either of water or of hydrochloric acid ; but as the 

 final result the gases are evolved, very nearly at least, in atomic 

 proportions, three volumes of hydrogen to one of nitrogen. 

 They can be collected separately in graduated bells as in the 

 electrolysis of water. In decomposing ammonia by chlorine, we 

 use with very satisfactory results the apparatus shown in fig. 6, 

 and already described. For this use, however, a tube should be 

 selected so thin that water may be boiled in it without risk of 

 breaking the glass. The tube having been filled by displace- 

 ment with pure and dry chlorine gas, we press down the lower 

 end into very weak aqua ammonise (eight measures of water to 

 one of the concentrated solution) until the liquid, flowing in 

 through the overflow-tube, rises to the height of the first rubber 

 ring. We now quickly close the delivery-tube with its rubber 

 cap and allow the absorption to continue until the tube is about 

 half full of the ammonia-water, when we also close the overflow- 

 tube and shake up the liquid in the large tube until all cloudi- 

 ness has disappeared from the interior. The decomposition is 

 now complete; but a considerable amount of the liberated nitro- 

 gen still remains dissolved in the liquid. To expel this we 

 heat the tube carefully over a gas-lamp until the liquid within 

 begins to boil. On now transferring the apparatus to the pneu- 

 matic trough and opening the overflow-tube under water, it will 

 be found, when the tube cools, that just one-third of the original 

 volume is left, and it can easily be shown that the residual gas 



a pressure considerably less than that of the atmosphere. For this purpose 

 a long eudiometer-tube should be used, and before each measurement the 

 level of the mercury should be adjusted so that it shall stand in the open 

 tube from 10 to 15 inches lower than in the eudiometer. Of course the 

 difference of level must be the same at both measurements. 



