312 Mr. Faraday on the 



one half had distilled over, the beak of the retort was intro- 

 duced into the tube before mentioned, and a small portion of 

 water (about fifty grains) condensed into it. A solid compact 

 piece of potassium was then chosen out, and having been wiped 

 with a linen cloth, was laid on a clean glass plate, the exte- 

 rior to a considerable depth removed by a sharp lancet, and 

 portions taken from the interior by metallic forceps, and drop- 

 ped successively into the tube containing the water before 

 mentioned. Of course the water was decomposed, and the 

 tube filled with hydrogen ; and when a sufficient quantity of 

 solution of potash had been thus formed, the tube was heated 

 in a lamp, and drawn out to a capillary opening, about two 

 inches from the closed extremity. The tube now formed al- 

 most a close vessel ; and being heated, as the water became 

 vapour, it passed off at the minute aperture, and ultimately a 

 portion of pure fuzed hydrate of potassa remained in the bot- 

 tom of the tube. The aperture of the tube was now closed, 

 and the whole set aside to cool. 



A piece of new glass tube w^as selected about 0*3 of an inch 

 in diameter ; it was heated to dull redness, and air passed 

 through it : about ten inches of it was then cut off, and being 

 softened near to one end by heat, it was drawn out at that 

 part until of small diameter': that part was then fixed into a 

 cap, by which it could afterwards be attached to a -receiver 

 containing hydrogen. The tube containing the potassium 

 potash being now broken in an agate mortar, a piece or two 

 of the potash was introduced by metallic forceps into the tube 

 at the open end, so as to pass on to the contracted part ; a roll 

 of zinc foil, about one grain in weight, cleaned with all the pre- 

 cautions already described, was afterwai'ds introduced, and 

 then more of the potash. The tube was then bent near the 

 middle to a right angle ; a slip of turmeric paper intioduced, 

 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 ex- 

 cess 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 



