1825.] On the Formation of Ammonia) fyc. 147 



the middle to a right angle ; a slip of turmeric paper introduced, 

 so as just to pass the bend, and thus prepared, it was ready to 

 be filled with hydrogen. 



. The precautions taken with regard to the purity of the hy- 

 drogen, were as follows : A quantity of water had been put into 

 a close copper boiler, and boiled for some hours, after which it 

 had been left all night in the boiler to cool. A pneumatic 

 trough was filled with this water just before it was required for 

 use. The hydrogen was prepared from clean zinc, which being 

 put into a gas bottle, the latter was filled entirely with the boiled 

 water, and then sulphuric acid being poured in through the 

 water, the gas was collected, the excess of liquid being allowed 

 to boil over. The hydrogen was received in the usual manner 

 into jars filled with the water of the trough, the transferring jar, 

 when filled, being entirely immersed in the water, so as to ex- 

 clude the air from every part, even of the stopcock. The first 

 jar of gas was thrown away, and only the latter portions used. 



The gas being ready, the experimental tube was attached to 

 the transferring jar by a connecting piece, so that the part of 

 it containing the zinc and potash was horizontal, whilst the 

 other portion descended directly downwards. A cup of clean 

 mercury, the metal being about an inch in depth, was then 

 held under the open end of the tube, and by lowering the jar 

 containing the hydrogen in the water of the pneumatic trough, 

 so as to give sufficient pressure, and opening the stopcock, the 

 hydrogen in the jar was made to pass through the tube, and 

 sweep all the common air before it. When from 100 to 150 

 cubic inches, or from 200 to 300 times the contents of the tube 

 had passed through, the cup of mercury was raised as high as 

 it could be, so as to prevent the passage of any more gas, the 

 pressure from the jar in the water-trough was partly removed, 

 and the stopcock closed ; then, by lowering the cup of mercury 

 a little, the surface of the metal in it was made lower than that 

 within the tube, and in this state of things the flame of a spirit- 

 lamp applied to the contracted part of the tube (a, fig. 3, plate I), 

 sealed it hermetically, without the introduction of any air, and 

 separated the apparatus from the jar on the water-trough. 



In this way every precaution was taken that I could devise 

 for the exclusion of nitrogen ; yet, when a lamp was applied to 

 the potash and zinc, the alkali no sooner melted down and 



