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.

Every half-hour or so stir the contents of the box with your stick, in order that they may thoroughly amalgamate. Lastly, when the whole is reduced to a thick, creamy-looking liquid, give a final stir, and pour the mixture into your tray, which you will have placed ready to receive it.

Most likely a number of air-bubbles will be floating on the surface of the liquid. These you must get rid of at once, or you will never be able to get off a clear and neat impression.

This part of the business is very easily managed. All that you need do is to heat your needle to a red heat, and touch each bubble in turn with the point. This treatment will cause them to burst, and by the time you have destroyed them all the composition will begin to set. For the next half-hour you must leave it perfectly undisturbed, upon a level surface, and at the end of that time it will be ready for use.

If all has gone well, your graph ought now to present the appearance of a pale yellow slab, yielding and rather clammy to the touch, and with a peculiarly glossy surface. This gloss will vanish after you have taken off your first impression, but that you need not trouble about.

When you wish to make use of your machine, write your letter or circular, or whatever it may be, with the special ink, and take care to make the up and down strokes as nearly as possible of the same thickness throughout. Let the writing dry, _without blotting it_, and then lay the sheet of paper face downwards upon your graph. Take care that in so doing you get no air-bubbles. If you do the result will be an uneven impression.

Now rub lightly with your finger over the whole of the paper as it lies upon the graph, in order to make sure that every part shall be in actual contact with the composition. Then, after about a minute or so, remove the paper very carefully, lifting it by one corner, and you will see that a reversed copy of the writing--a ‘negative,’ in fact--remains upon the graph.

Without loss of time take another sheet of paper, lay it upon the writing, rub as before, and remove after four or five seconds. An exact copy of the writing will by that time have been transferred to it, and by repeating the process you can take any number of impressions, up to fifty or sixty, that you may happen to want. As soon as you have printed off a sufficient quantity, wash your graph with _cold_ water, rubbing lightly with a piece of clean rag until the writing has almost disappeared. Then dry, and put away until again required for use. If you leave it for any length of time before washing, the ink will sink deeply into the composition. This will not matter once or twice, but if you make a practice of allowing it to do so your graph will in course of time be simply saturated with the ink and will assume a deep violet hue.

The copies which you will have taken will probably have absorbed some of the moisture from the graph and curled up into a kind of spiral form. These you can easily straighten by means of warmth and a little judicious pressure.

After you have used it a few times the surface of your graph will most likely become rough and uneven and unfit for further service. When this is the case, cut the composition out of the tray with an old knife and melt it down afresh. When thoroughly liquid, stir it well, pour it back into the tray, and eradicate the bubbles as before. Do not melt it down in the tray itself. If you do the glycerine will rise to the surface for want of proper stirring, and utterly ruin every sheet of paper you place upon the machine, obliging you to melt down the composition over again before it can be of the least use.

After melting the mixture some fifteen or twenty times you will find it necessary to add a little water, and perhaps a small quantity of glycerine also, in order to replace that which has passed off by evaporation. Be careful not to overdo it, however, for a very slight error in the proportions of the different ingredients will render the mixture useless.

Ink you had better buy; it is cheap enough, costing only about ninepence a bottle, and can be obtained almost of any stationer. You can manufacture it yourself, of course, by making a saturated solution of one of the aniline dyes (mauveine is the most powerful), and adding a few drops of glycerine, but, so far as my own experience goes, the home-made article is never really satisfactory, and does not give nearly the number of copies yielded by that which is specially supplied. Always procure violet ink in preference to black or red. It is far more powerful, and gives better and more numerous impressions.

N.B.--If you should happen to spill some of this ink on your fingers, wash them _at once_, or you will not be able to remove the stain without considerable trouble.

One word in conclusion. Never put your graph away while wet. If you do, the composition will absorb the moisture, the proper proportions will be altered, and before very long you will find that the printing power of your machine will be a thing of the past.