When you have put in your mixture, from which you intend getting the gas, do not heat your tube intensely at one spot at first, but move it through the flame so that it gets generally and gradually warmed. Care in this respect will save you a good deal of disappointment, and much destruction in gas-tubes and flasks.
If you want such a gas as oxygen on a larger scale, select an ordinary Florence flask, and fit it in the same way as we bare directed for the tube, and you will have such an apparatus as shown in Fig. 132. Select a flask in which the glass is of even thickness, and not a knotted or flattened flask. Some gases are given off at high temperatures from liquid mixtures, and require a safety-tube to the flasks employed. The flasks for this purpose have generally larger necks, because they require larger corks, through which two holes can easily be bored. In boring these take care that they are parallel, for it looks very badly to have one tube aslant to the other. The outer end of the safety-tube is generally supplied with a funnel. This you can manage for yourself. Hold the end of the tube in a gas-flame after it has been well warmed for some two inches of its length. While in this position keep it revolving between the hands. When the glass gets red-hot and soft, whirl it round a little faster; the softened glass will take the form of a funnel. When you have opened it out as much as you need, it must cool very gradually. In doing this, do not allow it to come in contact with any cool object, but hold it for some time in the heated air arising from your lamp. By this means it will become annealed; then it will not be liable to be broken with the differences of temperature to which such a tube must necessarily be subject when in use. If properly fitted, such a flask, when ready for use, is like that in Fig. 133. The funnel tube here shown is sometimes called a "thistle-tube."
Fig. 133. - Apparatus for hydrogen or carbonic acid gas. a. The india-rubber delivery-tube.
When the delivery-tube is long, it is likely to be broken. This danger may be averted by having it in two pieces, and joined by a length of india-rubber tubing. Cut off the tube you require for this purpose, a convenient length, with the file, according to the directions already given; then take about an inch and a half of small indiarubber tubing, of such a size that when slipped on to the tube it makes a tight fit. The ends can be fastened, if necessary, by being tied tightly with some pieces of twine, or fine copper wire; the latter undoubtedly holds best, because you can get a tight twist, and can also twist the ends up together as shown in Fig. 133, a. It is, however, better to have tubing fit without being tied.
For the making of hydrogen, carbonic acid, and such gases that require no heat, it is best to fit up a wide-mouthed bottle or flask, as in Fig. 133. Get a. good cork - or if you prefer it, buy a caoutchoue stopper through which two suitable holes are bored, and fit it up with similar tubes to those described in our last arrangement; then you will have such a piece of apparatus as is shown in Fig. 133. Bottles fitted in this manner will answer all the purposes for which Woulffe's bottles are recommended, and are of course very much cheaper.
We will now ask you to fit up a wash-bottle. Get an ordinary bottle with a fairly wide mouth; fit to it a good cork. Having selected your tubes, bore the holes the right size. Bend tube bt Fig. 134, at right angles; take care in bending it that the tube does not get contracted. This you can avoid by heating a good length of the tube in a flat gas-flame, but remove it from the flame before you bend it, as we have before mentioned; but being important it is worth repeating. For tube a, you must have one long enough to reach the bottom of the bottle, and at the other end get a graceful bend; before bending it, you had better form the "jet" end. This you must b by softening the glass-tube in the gas flame, then drawing it out to the fineness needed. Let it cool. Then break off the end; heat the tip in the flame to take off the rough edges, and you have a jet as in the " tip " of Fig. 136. Now fit these bent tubes into the cork, and you have such a bottle as shown in Fig. 134. A fiat-bottomed flask is sometimes employed for making a wash-bottle. The outside portions of the corks in all these arrangements are improved in appearance by the use of a little "philosopher's" paint, as it is called. This is made by dissolving some good sealing-wax in methylated spirits. Dilute it down to a convenient consistency, and put on smoothly with a camel's-hair brush. Do not use the apparatus till this paint gets quite hard, for if fingered too soon it takes impressions of the skin of the fingers, and also takes the gloss off it. In about two or three days it will be quite hard enough to handle if you do not put it on too thickly. Next fit up a bottle for making hydrogen sulphide. Get a white or green glass bottle, as was mentioned for ordinary hydrogen - a pickle-bottle will do. A good cork must be fitted to it and the funnel and delivery-tubes, and a second bottle must be provided as a wash-bottle, which should be somewhat smaller than the generating-bottle. Instead of the delivery-tube being fitted to the bottle in which the materials are put for making the gas, it must be put into the wash-bottle. The wash-bottle must be fitted as shown in Fig. 135. The corks in both bottles must be exceedingly well fitted, and the tubes must exactly fit the holes. Notice that in the wash-bottle the tubes from the supply-bottle must reach nearly to the bottom of the jar. The whole ready for use is shown in fig. 135.