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 pur- 

 poses 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, black- 

 smith, 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 anilin 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 var- 

 nish 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 



Ani^in Oil 1 20 cc. 



Hydrochloric Acid 180 cc. 



Water 1000 cc. 



Mix these in a glass vessel putting in the water first. Apply two coats with- 

 out 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 Micro- 

 scope, by Gage, nth cd. 1911, pp. 282-283). 



