CH. IX a} PROJECTION MICROSCOPE 



position of the hand. It is a very convenient form of attachable mechanical stage 

 on account of its wide range of movement and because it receives double slides, 

 50x76 mm. and those of standard size. 



ACKNOWLEDGEMENT 



The Author wishes to express his appreciation of help obtained from Sibley 

 College in designing and constructing the lathe bed and the movable pieces carry- 

 ing the parts of the projection microscope shown in Fig. 204. Thanks are 

 especially due to J. L. Morris, Sibley Professor of Practical Mechanics and 

 Machine Construction for the interest shown and the very practical help in direct- 

 ing the work. Thanks are also due to Mr. James Wiseman, Foreman in the 

 Machine Shop for the accuracy and excellence with which the work was carried 

 to completion. 



BLACKENING TABLES 



As stated in the preceding pages it is a great advantage to have everything 

 dead black in connection with the Projection Microscope. It is also desirable to 

 have photographic tables and laboratory tables black. 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 icoo 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 icoo 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, sand paper the wood and dust off the excess 

 chemicals. Then wash the wood well with water. When dry sand paper 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. 



