An art that can only be acquired by practice. Suppose it is desired to make a sealed tube with a bulb at one end, a piece of glass tube of the deiiired size and lengthsay t inch diameter and 4 or 5 inches in lengthis taken, and one end placcd in a Bunsen or blowpipe flame until the glass softens sufficiently to mass together, close up, and become solid to the extent of about i inch. Whilst still redhot and soft, the mouth should be applied to the open end, turning the tube round in the fingers, and meantime blowing with enough pressure to swell out the molten glass. It may be necessary, and often is so, to reheat the blownout part and repeat the blowing until a bulb of the right size and shape is obtained. Bulbtubes thus prepared are useful for observing the behaviour of solid chemical substances placed in them for that purpose when heat is applied. The conveyance to the bulbtube of the substance to be examined can be easily effected by the use of a sharply channelled slip of paper. Iodine will be seen to volatilize, and give off fumes of its own colour, and to recondense to the sold state in the upper part of the tube. Sulphur can be seen to melt and pass through the stages described under that heading, including sublimation and recondensation. Mercury can be sublimed and seen to condense on the upper cool part of the tube so also ammonium chloride. Lead filings can be melted in the bulb. White lead is decomposed, carbon dioxide being given off as gas, and yellow litharge being left behind in the tube. Glass Tpieces can be made with a little practice, and are often wanted in the laboratory. Take a piece of glass tube of the desired length, and plug one end with a small boring of cork then hold it in the flame of a blowpipe so that a fine tongue of flame impinges upon and heats the tube in one spot only, near the middle; and when it is observed to be redhot, remove the tube from the flame and place the open end quickly in the mouth. Upon blowing, the molten part will become distended into the shape of a swelling or balloon, so thin that it can easily be broken, thus lea> ing a hole in the tube, the edges of which can be rounded off with a file. Next, take another piece of glass tube and blow a bulb at one end as previously described, taking care, however, in this case to blow the bulb as large, and therefore as thin, as possible. This bulb is then to be broken and the edges rounded off as in the other case with a file, when it remains to join the two pieces together. We have then the one tube with a hole in its centre, and the other tube with one end provided with a sort of lip roughly fitting the hole as to size. The flame of the blow pipe should now be applied to both these parts, and when sufficiently softened by the heat they can be joined together in the flame.
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