Most of our readers have learnt something of science at school, or at the evening classes in connection with their school or recreative classes.
Chemistry is the science generally taken first, because, as a subject, it is most important, and the ordinary experiments are performed with apparatus and material much less costly than that required for many other branches of science.
Having seen the experiments in class, most pupils, if they take any real interest in their work, are anxious to repeat the experiments themselves. And this is very desirable; for the performance of an experiment is a much better way of getting to understand the subject than merely seeing the experiment performed.
A little patient ingenuity will enable you to acquire a fair stock of apparatus for the repetition of ordinary experiments. Test-tubes, flasks, and 1 lb. of glass-tubing of various sizes, a few good soft corks, a small set of cork-borers, a triangular file, a small rat-tailed file, are the first requirements. You must have access to, and the use of, a gas-burner or a good spirit-larnp, and a ninepenny Black's blow-pipe. Working in glass forms also a nice change of occupation from carpentering - the manipulation is so different - the toughness of the wood forming a very strong contrast to the brittleness of the glass.
We always find a pupil gets on so much better with his work if he repeats the class experiments himself, and much better still if he makes his own apparatus. He is more interested in his work, it widens his knowledge, and gives him a thoroughness that he would not otherwise be able to acquire. Above all things, it makes him practical.
Fig. 130. - Apparatus for preparing oxygen gas.
We feel sure that after learning to make the simple things mentioned in this chapter, he will go on to the more difficult contrivances which we dare not even hint at here.
As the subject, oxygen, is generally the first gas dealt with, we will describe a simple apparatus for making it. The apparatus for making gases that are only given off by heat, must be made of thinner glass than that for gases which are given off at the ordinary temperature ofthe air.
We will suppose you want a small apparatus for making a little oxygen. Take a test tube ¾ inch by 6 inches - the best way is to buy a few tubes of various sizes from ½ inch x 4 inches up to ¾ inch X 6 inches; these will be the most useful sizes. Select a good soft cork to fit the tube. You can soften the cork by squeezing it; this is generally done by the ordinary cork-squeezer, but very likely you will not have one. You must therefore wrap up the cork in a piece of paper and roll it on the floor, under the foot, regulating the pressure on it as may be required. Having fitted your cork to the tube, the next thing is to fix a delivery-tube. This you must select before boring the cork. Choose the borer somewhat smaller than the tube. The borer is a brass tube with sharp cutting edges, as shown in Fig. 131, which should be carefully kept, so that the cutting part does not get turned up by coming into rough contact with your file, or by falling on a hard floor,, for the edge is soft, and only adapted to cut such soft substances as cork. Cork-borers are sold in sets (Fig. 131). To bore the cork, put a stout wire through the hole at the upper end of the barrel of the borer; hold the cork firmly in the left hand, pressing it down on a board, or hold it flush with the edge of the board. Begin with the smaller end of the cork. Hold the borer at right angles to the top of the cork ; then with a slight pressure turn it into the cork, till you find it through the other end. Draw out the borer, and with the wire posh out the core from inside of the tube and pat it away - the borer may then be smeared over with a little petroleum to keep it bright Now just moisten the end of the glass-tube selected for the delivery-tube, and put one end into the cork by holding the tube lightly between the thumb and the finger of the right hand, and the cork in the left, twisting the tube and pressing it at the same time. It should fit very tightly.
Fig. 131. - Set of Cork-borers.
The next process is to bend the tube to give it "two elbows." The best way to do this is to hold it in a flat flame, the first portion being near to the cork - it will form a handle for you - the tube must be twisted round, and moved light and left so that several inches of the tube get heated. Let it get hottest at the portion you want to make the bend. When red-hot remove it from the flame, and bend it to the angle required; bend it gently, so that it may not have a sharp bend, or it may break. Do not let it cool suddenly, but hold it at some distance above the flame for a short time, and do not wipe off the soot with which it will be covered for some time - not till it is quite cold. By this means it gets "annealed." The other end - "the delivery-end" - must be heated in the same way, and bent slightly upwards.
It is better to cut off the tube to the proper length before fitting it. A good length is about 12 inches from the cork. Take the tube at this point lightly between the fingers, hold it firmly down on a board, and give a deep scratch with a sharp triangular file. With a small tube, this one scratch will be enough. Now hold the tube tightly, bring the thumbs close up to the scratch, with the scratch upwards; break the tube by sharply snapping it downwards. If the tube is too thick for this, scratch the tube half round, or even more, and then break it off. The broken end will be sharp, and must be held in a gas-flame till it is red-hot, then the sharp edges will become round. If you have finished your apparatus properly, it will have the appearance of Fig. 130. Sometimes, even with the best corks, the fit between the cork and the tube is not the most perfect. If not perfect the gas, when given off, will escape; this may be prevented if a little pipe-clay be moistened and spread round the cork, and pushed well down to the edge of the tube. Keep a block of pipe-clay for similar use in other apparatus; it is much better than paste or dough.