The Boy's Own Book of Indoor Games and Recreations / A Popular Encyclopædia for Boys

by C. Stansfeld Hicks; John Nevil Maskelyne; Gordon Stables

Fig. 9.

The method of charging the apparatus is as follows. Put into the retort about a pound and a half of oxygen mixture; pour into the purifier a sufficient quantity of water to about two-thirds fill it. Place the retort on a clear but not fierce fire, or over a gas furnace, and unite it to the long tube of the purifier (B). Attach the short pipe from the purifier to the gas-bag, and open all the taps, so that there may be a free passage-way from the retort to the bag. In a few minutes the gas will be given off, and will manifest itself by rising in bubbles through the water in the purifier. If a fierce fire be employed, the gas will be given off with undue rapidity and will pass through the purifier in volumes, so that it only becomes partially washed. A rapid but regular succession of gas is most to be desired. Should the gas come off with great violence, the retort should be lifted from the fire without disarranging the apparatus, and when the excessive rapidity is moderated it can be replaced. It is not, however, desirable to remove the retort from the fire if it can be avoided, for it not unfrequently happens that when the retort cools down, with only partially decomposed material in it, waste is the consequence, as it is not quite easy to re-establish the decomposing process. When the gas has entirely come off—which may be known by the cessation of the bubbles in the purifier—the top of the bag should be closed, the retort taken from the fire, detached from the purifier, and stood aside to cool. When cold, the residuum may be readily washed out with water, and when dry, the retort is ready for use again. The purifier should be emptied and washed out also. Always blow through the flexible tubes leading from the retort to the purifier, and wash out the metal tube of the retort in order to remove any solid material that may have been deposited there from the gas.

There has recently been manufactured a very neat oxygen gas-generator and gas-burner combined. The inventor proposes to prepare the oxygen in the room where the exhibition is taking place, and while using the lanterns. But as this apparatus would be very difficult to manipulate with, even by an experienced operator, it cannot be recommended for general use.

With regard to the hydrogen gas, it is always best to use the ordinary house gas, or if that cannot be obtained, to use the oxycalcium lamp, as the preparation of the pure hydrogen gas is troublesome, and not quite free from danger.

10.—SLIDE PAINTING, ETC.

The preparation of magic-lantern slides for home use (although, perhaps, not equalling the bought ones in quality) is a great source of pleasure, and a few hints on this part of our subject will probably be acceptable. A number of very amusing slides may be made by cutting grotesque or other figures out of black paper, and pasting them on glass slips, and after the pictures are dry, giving a little detail by slashing the picture with a sharp penknife in places where needed. If these figures be first drawn on tissue paper, coloured, and then cut out, the effect is still more pleasing. Or, if preferred, sheets of these figures in black can be bought, and thus the trouble of drawing them will be saved.

A very efficient set of astronomical slides may be constructed out of blackened cardboard with the aid of a few punches, some different-sized needles, and some of the coloured gelatine bon-bons. Having cut the card of a size suitable for the lantern, and marked on it a circle of the same diameter as the lantern condenser, prick holes in the card by aid of the needles, so as to represent the principal constellations and nebulæ, illustrations of which will be found in most works on astronomy. The relative positions of the planets may be shown by punching holes in the cardboard and covering them over with gelatine. When the holes are punched, the orbits may be traced by a very minute row of holes, pricked with a fine needle, the circles having first been marked with a pair of compasses.

For larger diagrams representing the planets singly, a sharp penknife and a pair of compasses would, combined with a steady hand, produce wonders.

The painting of magic-lantern slides on glass is a rather more difficult task, and some knowledge of the rules of the art of painting in general will be found most useful. The colours and brushes to be used are sold in boxes, and the number of colours can be readily increased by mixing. The following articles may be considered necessaries. Easel, glass to paint on, pencils, dabbers, etching-needles, fixing varnish, and the following colours: Blue, Nos. 1 and 2, crimson, amber, brown, mauve, black, light green, dark green, orange, purple, and scarlet. Having obtained these articles, proceed as follows. Make a drawing of the picture required, of the right size, on white paper, and place this under the glass upon which the picture is to be painted. The outline is then to be traced on the glass in Indian ink with a fine pen. This part of the work, however, can be dispensed with if the glasses be bought having pictures already outlined on them. If the subject of the picture be a landscape, the outlined glass is to be turned upside down, and the sky filled in first, commencing at the horizon with a pale tint, which is to be increased in density as the edge of the picture is approached. To remove any superfluous colour, a dabber is used.

When this colour has dried, the other parts of the picture are painted in succession with appropriate tints, warm tints being employed for the objects in the foreground, neutral or cool tints for the background.