ftO Mr. Faraday on the 



course the water was decomposed, and the tube filled with hydro- 

 gen ; and wlien 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, 

 (fig. 1. plate.) The tube now foi-med almost 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 bottom of the tube. The aperture of the tube 

 was now closed, and the whole set aside to cool. 



A piece of new glass tube was 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 dra\vn out at that part until of small dia- 

 meter : (a, fig. 2. plate.) 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 me- 

 tallic 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 precautions already described, was afterwards 

 introduced, and then more of the potash. The tube was then bent 

 near the middle to a right angle ; a slip of turmeric paper intro- 

 duced, 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 col- 

 lected, the excess of liquid being allowed to boil over. The hydro- 

 gen was received in the usual manner into jars filled with the water 

 of the trough, the transferring jar, when filled, being entirely im- 



