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The most primitive method of making coal gas on a small scale is to fill a tin—which must have folded, not soldered, joints—with small coal, punch a hole in the bottom, and place it lid downwards in the fire. Gas soon begins to issue, but, owing to the quantity of moisture and impurities present, it will not ignite until some minutes have elapsed. The flame, when it does make its appearance, is very smoky and gives little light, because, in addition to the coal gas of commerce, there are present ammonia gas, sulphuretted hydrogen, carbonic acid, tar vapour, etc., which prevent brightness of flame. [Illustration: FIG. 190.—General view of gas-making apparatus.] A miniature gasworks, if it is to be worthy of its name, must obviously endeavour to separate the troublesome components from the useful gas. The doing of this involves several processes, all simple enough in principle, and requiring but simple apparatus for demonstration on a small scale. To take them in order the processes are— (l) The formation of gas in a retort; (2) The condensation of the tar; (3) The condensation of steam; (4) The removal of the ammonia gas; (5) The removal of the sulphuretted hydrogen and carbonic acid. The last two processes are, in a real gasworks, usually separated, but for simplicity’s sake we will combine them. Finally, the storage of the gas has to be provided for.