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CH. IX] HOME-MADE PROJECTION APPARATUS 289
another and be ready for projection by connecting the supply wires for the lamp to the line at any outlet box (fig. 3).
§ 425. Lathe bed or optical bench for projection apparatus. —
For the projection microscope, and for general experimental purposes there is no form of projection outfit so suitable and flexible as the lathe-bed type. It is easily and cheaply constructed. Any teacher with a little ingenuity and the aid of a tin-smith, blacksmith, plumber, and carpenter or cabinet-maker, can construct all except the optical parts. The optical parts can be obtained of dealers or manufacturers of microscopes and projection apparatus. There is this further advantage in getting up a projection outfit, the person who does it will know enough to use it. He will not
§ 424a. Stain for laboratory tables. — During the last few years an excellent method of dying wood with anil in black has been devised. This black is lustreless, and it is indestructible. It can be removed only by scraping off the wood to a point deeper than the stain has penetrated.
It must be applied to unwaxed or unvarnished wood. If wax, paint or varnish has been used on the tables, that must be first removed by the use of caustic potash or soda or by scraping or planing. Two solutions are needed :
SOLUTION A
Copper sulphate 125 grams
Potassium chlorate or permanganate 125 grams
Water 1000 cc.
Boil these ingredients in an iron kettle until they are dissolved. Apply two coats of the hot solution. Let the first coat dry before applying the second.
SOLUTION B
Anilin Oil 120 cc.
Hydrochloric Acid 180 cc.
Water 1000 cc.
Mix these in a glass vessel putting in the water first. Apply two coats without heating, but allow the first coat to dry before adding the second.
When the second coat is dry, sandpaper the wood and dust off the excess chemicals. Then wash the wood well with water. When dry sandpaper the surface and then rub thoroughly with a mixture of equal parts turpentine and linseed oil. The wood may appear a dirty green at first but it will soon become ebony black. If the excess chemicals are not removed the table will crock. An occasional rubbing with linseed oil and turpentine or with turpentine alone will clean the surface. This is sometimes called the Danish method, Denmark black or finish. See Jour. Ap. Micr., Vol. I, p. 145; Bot. Zeit., Vol. 54, p. 326, Bot. Gazette, Vol. 24, p. 66, Dr. P. A. Fish, Jour. Ap. Micr., Vol. VI., pp. 211-212. The Anatomical Record, Vol. V. 191 1, pp. 145-146. (Quoted from The Microscope, by Gage, nth ed. 1911, pp. 282-283).