Or, upon a small sheet of any metal, place a few grains of iodine, and add a chip of dry phosphorous; when the latter will inflame, and the iodine pass off in a violet vapour. TO COLLECT GASES. Provide a moistened bladder, tie a piece of tobacco-pipe firmly into its neck, twisting it so as to expel the common air. This may be fitted to any vessel by means of the pipe, which may be fixed in the cork of a bottle containing gas, and closely luted with putty or clay, or powdered lime and white of egg. THE DEFLAGRATING SPOON. To introduce substances into gases, a deflagrating spoon is required. It may be bought for half-a-crown; but an instrument equally useful may be made as follows: cut a piece of sheet copper somewhat larger than a sixpence, and bend it into a shallow, cup-like form; twist four fine brass wires, each nine inches long, tightly together, leaving an inch at the extremities, which must be spread to hold the copper, as the strings or chains of a balance support the scale-pan. To complete it, take a piece of sheet-lead, the size of a penny-piece; make a hole through the centre large enough to admit the twisted wires, but, at the same time, retaining them firmly in their position: then, if the wires will not rest in the lead by adhesion, the hole may be enlarged, the wire put in, and secured by a piece of solder. The spoon being then let down through the mouth of a bottle, the circular piece of lead rests upon and stops the mouth. WHAT IS STEAM? Invert a glass goblet over a cup of hot water, when the vapour or steam will be seen to rise in it, to condense upon the cold glass, and then to run down its inside; thus showing that steam is vaporized water, and will, when the heat is abstracted from it, become water again. THE STEAM-ENGINE SIMPLIFIED. The steam-engine is much more intelligible than its name first suggests. That part by which the machinery is set in motion, may be compared to a syringe, or squirt, the rod of which is driven up and down by steam admitted above and below, one end of the rod being connected with the machinery to be worked. Thus, the piston is made to turn the wheels of a railway carriage, or the paddles of a steam-boat.