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 hydrogen, 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 exclude 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
