708 SUMMARY OF CURRENT RESEARCHES RELATING TO 



For making the lantern-slide the Paget plate gives the best results, 

 and the warmer tones of brown, purple, and red are superior to black 

 and white effects. Proper matting is of the greatest importance ; the 

 mat should be capable of being cut to suit the subject, e.g. the Boston. 

 The developer is made up as follows : — Hydrochiuon 100 grin., sodium 

 sulphate 400 grm., sodium carbonate 400 grm., water 20 oz. The 

 dilution of the developer is made as follows. (1) for black tone : 

 developer 1 oz., water 2 oz., 10 p.c. solution of bromide 1-2 drops ; 

 exposure 20 seconds. (2) For brown tone : developer 1 oz., water 

 4 oz., bromide 5-8 drops; exposure 1^-2 minutes. (3) For red tone : 

 developer 1 oz., water 8 oz., bromide 15-25 drops ; exposure 5-15 

 minutes. (4) For purple tone : over-exposure and No. 2 dilution. 

 The temperature of the developer should be from 70° to 80°. In 

 making slides the best results are obtained by using a reducing and 

 enlarging camera in preference to making slides by contact with the 

 negative. Wben the section is well differentiated, the following pro- 

 cedure is advised : — A lantern-slide is made with the reddest tone 

 obtainable. After fixing and washing, but before the slide is dry, it is 

 toned in a gold-bath made as follows : (1) sulphocyanide of ammonium 

 200 grains, water 32 oz., carbonate of soda 2 grains ; (2) chloride of 

 gold 15 grains, water 1 oz. Add 4 drops of No. 2 to 2 oz. of No. 1, and 

 immerse the red slide long enough to permit the gold to attack the 

 lighter deposit of silver in the film. The temperature of the gold- 

 bath should be from 72° to 76°. After fixing the Paget plate, swab 

 it over with a tuft of cotton immersed in a solution of ferricyanide 

 of potash of the colour of very pale sherry. 



For making the enlargement a rather weak negative is used. 

 Parallel light is obtained by means of an arc lamp and a condenser so 

 arranged that the arc is at its focus. Only the central portion of the 

 condenser is used. The finest medium focus, double series, view lens 

 is used for projection, and it is well stopped down, say, to F.-16. A 

 paper made by Eastman is tacked to a board absolutely at right angles 

 to the axis of the projection beam, and enough time is given to ensure 

 the obtaining of every detail of the image. Developing is done in 

 adurol, one portion of developer to about 30 of water, and bromide 

 added according to the character of the image required. Then wash, 

 and place in a weak solution of hypo, with a saturated solution of 

 chrome-alum added in the proportion of 1 to 20. A very weak solution 

 of formalin may be used after the print has been partially washed upon 

 removal of the hypo solution. Wash thoroughly, and hang up to dry. 

 Adurol gives a brownish tone just off a black, and imparts life to the 

 image. 



In making enlargements from a negative with clear glass sur- 

 rounding the microscopic image, the light of the arc lamp should be 

 cut off from the surrounding area by backing the negative with dense 

 yellow paper cut to the requisite size. The size of the image on the 

 negative should be reduced by allowing the paper to lap down upon the 

 image. This gives a clear cut edge to the circle when enlarged upon 

 the bromide paper. 



