THE AMERICAN 



MONTHLY 



MICROSCOPICAL JOURNAL. 



Vol. XII. AUGUST, 1891. No. 8. 



All cominunicatio7is for t Ids Journal, whether 7-elating to business or lo editorial 

 matters, and all books, pamphlets, exchanges, etc., should be addressed to Ameri- 

 can Monthly Microscopical Journal, Washingto7i, D. C. 



European subscriptions may be sent directly to the above address accompaftied 

 by Internatio7ial Postal Order for $i.i§ per aiimim, or they may be sent to Messrs. 

 Trilbner &^ Co., j/ Ludgate Hill, London, or to Mr. W. P. Collins, 757 Great 

 Portland street, London, accompanied by the yearly price of five shillings. 



The Value of Using Different Makes of Dry Plates in Photomicrog- 

 raphy. 



By W. C. BORDEN, M. D., U. S. A., 



NEW ORLEANS, LA. 



[With Frontispiece.] 



While the variation in rapidity of different makes of plates is pretty 

 generally understood and taken advantage of in practical work, the 

 variations of plates in contrast and range of tones are not generally dis- 

 cussed in photographic literature, nor are the great advantages to be 

 obtained by taking proper advantage of these variations understood, or 

 generally practiced. Hardly a photographic journal appears without 

 either some new^ formula for a developer, or some new method of work- 

 ing an old one, by which it is claimed that some modification of rapidity 

 or contract maybe produced in the plate qn which they are used. 

 Qiiite a large portion of photographic literature is devoted to giving 

 these means of producing required effects in negatives, and every box 

 of plates contains information ( .^) how to obtain greater or less rapidity, 

 or contrast, as may be desired ; when in fact, after the light has once 

 struck a plate in a particular way, so changing in a particular ratio, the 

 molecular structure of the sensitising chemicals with which it is coated, 

 but little change in result can be produced by any developer, however 

 much that developer may be modified. A modification, however, of 

 the coating of the plate, giving a different chemical basis upon which 

 the light acts, will, from the different arrangement and kind of molecules 

 acted upon, produce a different result whatever developer may be em- 

 ployed. It is in this way that variations in result may be best and most 

 surely obtained, for different makers of plates use sensitizing formulas 

 differing in such manner that the coatings, when acted upon by light 

 and " developed " give, results differing in rapidity, contrast, and range 

 of tones. That almost universal advice : '' Get a good plate, master its 

 peculiarities, and then use this plate exclusively," is good only so far 



Copyright, 1891, by C. W. Smiley. 



