THE AMERICAN 



MONTHLY 



MICROSCOPICAL JOURNAL. 



Vol. YII. 



Washington, D. C, August, 1886. 



No. 8. 



Photo-Micrography. — VIII. 



BY THE EDITOR. 

 \_Conti7izied from page /JJ.] 



The treatment of negatives after de- 

 velopment is sometimes necessary in 

 order to give good printing strength 

 to such as are thin, and to reduce the 

 density of such as are too dense. The 

 methods of operating are many, but 

 it will generally be found that the 

 simplest are the best. 



Intensification. — Prepare a satu- 

 rated solution of corrosive sublimate 

 in water, pour it into a tray and im- 

 merse the developed and fixed plate 

 in the solution. This may be done 

 immediately after the hypo-sulphite 

 is washed out of the film, or at any 

 subsequent time after the plate is 

 dry, in which case the film should 

 first be thoroughly soaked in water 

 to ensure uniformity of action. The 

 operation is finished when the film is 

 whitened through, so that it appears 

 white when looked at through the 

 glass. It must then be thoroughly 

 washed in water, and blackened by 

 flowing with weak ammonia, or with 

 a not very strong solution of soda sul- 

 phite, the latter being preferable to 

 the ammonia. Then wash and dry. 



Sometimes it is possible to increase 

 the brilliancy of a flat, over-exposed 

 negative in this way, especially if it 

 is first subjected to the action of the 

 cyanide reducing solution mentioned 

 further on, but there is then liability 

 to destroy the details, and such pre- 

 liminary treatment must be applied 

 with great judgment, or it will do 

 harm. As a rvile, it is better not to 

 intensify negatives, for they are sure 



to lose something in softness and 

 beauty. 



A diflerent form of the mercury in- 

 tensifier is prepared as follows : — 

 Corrosive sublimate ... 3 parts. 

 Potassium bromide ... 2 " 

 Water loo ^ 



Put the negative in the solution, as 

 before described, and after thorough 

 washing darken the deposit with the 

 sulphite. Those who prefer to use 

 definite weights in preparing the sul- 

 phite solution may dissolve one part 

 of the sulphite in six parts of water. 



Reducing density. — This is an 

 operation sometimes necessitated by 

 over-development. It is not to be 

 applied to under-exposed plates to 

 diminish contrasts, except in such 

 cases as permit of the local appli- 

 cation of the reducer, for to apply 

 it over the whole plate would only 

 make the contrasts greater by re- 

 moving the detail in the shadows. 

 The method we prefer is a very old 

 one, but, if we may judge from the 

 current photographic literature, it is 

 not in great favor among operators 

 generally. It is useless to give ex- 

 act proportions, for they will neces- 

 sarily be varied to suit each case. 

 Take a piece of potassium cyanide 

 about the size of two peas and dis- 

 solve it in about four ounces of 

 water. Make a solution of potas- 

 sium iodide in an ounce of water, 

 and dissolve in that sufiicient iodine 

 to make a strong solvition. Then 

 moisten the plate in water, take it 

 in the hand by one corner and flow 

 over it the cyanide solution with a few 

 drops of the iodine solution added to 

 it. If no reduction in strength is ob- 



