ash, a portion of that alkali was prepared from potassium; and as the. experiment made with it includes all the precautions taken to exclude nitrogen, I will describe it rather minutely, as illustrative of the way in which the other numerous experiments were made. A piece of new glass tube, about half an inch in diameter, was first wiped clean, and then heated red-hot, a current of air passing at the same time through it; about six inches in length was drawn off at the blowpipe lamp, and sealed at one extremity. Some distilled water was put into new glass retort, and heated by a lamp; when about one-half had distilled over, the beak of the retort was introduced 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, and having been wiped with a linen cloth, was laid on a clean glass plate, the exterior to a considerable depth removed by a sharp lancet, and portions taken from the interior by metallic forceps, and dropped 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 (fig. 2, plate I). The tube now formed 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 fused 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 10 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 (a, fig. 3, plate I): 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 were 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 precautions already described, was afterwards introduced, and then more of the potash. The tube was then bent near
