78 THE MICROSCOPE. [May, 



154. What is the ??wst convenient and best method for pro- 



ducing monochromatic illumination? What are the formula: 



for the atnmonio-cupric solution and the sodium flame? — F. P. 



The best method for producing monochromatic illumination is 

 by the use of expensive prisms, as described in Carpenter, 7th 

 ed., pp. 272 and 360. The most convenient method is by the 

 use of cobalt blue glass. Ammonio-sulphate of copper may be 

 made as follows : Take a saturated solution of sulphate of copper 

 in water, add strong aqua ammonia until the precipitate at first 

 formed is redissolved. The resulting deep blue solution, in a flat- 

 sided tank, is placed between the source of light and the object. 

 The sodium flame is best produced by dissolving a sodium salt 

 (sodium salicytate or caustic soda) in alcohol and burning it in 

 an ordinary alcohol lamp. The flame is deep yellow in color, 

 but of very feeble illuminating power. 



ijj. Can you give me information in regard to making 

 microphotographs {jninute photographs on glass, not the en- 

 larged photomicrographs} or refer ?ne to any book upon the 

 subject ? — A. 



There is practically no practical literature on the subject, but 

 a method may be worked out by an ingenious person. The fol- 

 lowing outlines of a method which has been successfully used 

 may be of assistance : Make a small camera to take a plate, say, 

 1 j x 2 inches (a quarter plate cut in 4). Use a plain glass dabbed 

 with putty for a " ground glass," to set against a strip of glass 

 top and bottom, with spring clips to hold it. An inch objective 

 in a smoothly sliding tube for focusing will serve as the photo 

 lens. Have stops or pegs on the supporting-board or table, so 

 the whole camera may be removed to tne dark room, a sensitized 

 plate slipped in place of the " ground glass," and the whole re- 

 placed in the former position ; the back of the camera closes with 

 a slide or door. If this combination camera and slide-holder is 

 made wide enough a screw or rod through the side may be ar- 

 ranged to press against the plate and move it sidewise to several 

 new positions, and thus allow of several different exposures of the 

 same negative, the whole to be developed together and subse- 

 quently cut apart. The negative to be copied must be set up 

 several feet away and very carefully and evenly illuminated. 

 Focus on a prominent black band or mark painted on the nega- 

 tive film. Use a hand-lens to secure a sharp image. It will be 

 necessary to make allowance for the different focal points of visual 

 and chemical rays, unless the objective has been specially cor- 

 rected for photo use. The old collodion wet process will probably 

 produce the finer results in these minute transparencies. Devel- 

 opment will be simply guess-work until experience is gained. 



A microscope stand has been used in this way : Remove the 

 eyepiece, direct the tube horizontally toward the illuminated nega- 



