REV. A. N. MALAN, M.A., F.G.S.
CHAPTER XXXI.—GRAPHS AND GRAPH-MAKING.
By Theodore Wood.
Although for the last year or two its popularity has been somewhat on the wane, there can be no doubt that the copying machine, known by the various titles of chromograph, hektograph, multigraph, centograph, and others of similar nature, is a most useful invention, and one which saves an immense amount of labour to all those who wish to draw out a number of copies of diagrams, plans, circulars, letters, music, etc., without calling in the assistance of the printer. Drawings, too, may be traced by those who have no original artistic powers, programmes may be made out for entertainments, and in a hundred other ways the machine will prove a most profitable investment. Its chief disadvantage lies in its expense, but as the entire machine can easily be made at home for a very small cost, this drawback is more apparent than real.
The process of graph-making is a very simple one, and cannot fail if the directions which I am about now to give are implicitly followed.
The apparatus required is of a very limited character. First you will want an old tin biscuit-box, sound as to the corners, and of moderate depth. A saucepan would answer better still, but as you would probably never get it clean again, I do not recommend its use. Then you will require a short stick or rod with which to stir the composition, a spirit-lamp (or a gas-jet will do nearly as well), and a stout carpet-needle fastened into the end of a wooden handle. Finally, you must have a shallow tray to hold the composition, and also the ingredients themselves.
The tray must be of metal, and nothing will be better for this purpose than the lid of your biscuit-box, unless you wish to make a graph of phenomenal proportions. In that case, of course, you must get an ironmonger to make you a tray of the required dimensions, and be prepared to add an extra shilling or so to the necessary outlay. For all ordinary purposes, however, you cannot improve upon the box-lid.
Now as to the ingredients, which, for a graph of medium size, will be as follows:—Glycerine (common), eighteen ounces; water, twelve ounces; sulphate of barium, six ounces; powdered loaf-sugar, three ounces; Nelson’s gelatine, three ounces. The first and the third of these you had better get at a manufacturing chemist’s; ordinary druggists are apt to charge rather highly for the former, and do not keep the latter in stock. Each ought to cost you one penny per ounce. Nelson’s gelatine you can procure from almost any respectable grocer at fourpence-halfpenny per one-ounce packet. The total cost, therefore, of the compound should not exceed three shillings and twopence.
Everything being in readiness, place the ingredients in your biscuit-box, taking care that the proportions are measured correctly, and place them on one side for four-and-twenty hours—this in order to allow them to macerate. Next day you will find that the gelatine has swollen to a wonderful degree, and has absorbed most of the water. Still, however, the mixture will be very far from perfect, and in order to complete it you must have recourse to heat. The best thing that you can do is to place the box upon the kitchen stove, and there leave it for two or three hours until the gelatine has melted. Take care, however, that the heat is not too great, or your composition will probably be spoiled.