﻿254 Messrs. Trivelli and Kighter on Silbersteins 



an estimate of the areas of all clumps one and the same 

 average grain size (area) had been assumed throughout. 

 Upon recalculating the results, however, and assigning the 

 correct average grain size (area) to the single grains and to 

 the different clumps, the very interesting fact was observed 

 that the average grain size (area) increases from the single 

 grains to the clumps of two, three, etc. The corrected results 

 conform, even better than expected, to the above formula, 

 with a finite a. 



Experimental. 



These experiments, although of an extremely tedious and 

 trying nature, were performed with the utmost care and, to 

 the best of our knowledge, all sources of error were either 

 eliminated or reduced to a minimum. Only a brief descrip- 

 tion of the experimental procedure will be given at this 

 time, as a more extensive paper containing further experi- 

 mental results is to be published in the near future with a 

 detailed account of our methods of photomicrography, and 

 in which all errors will be discussed fully. 



A simple silver bromide emulsion was used for these 

 experiments having a speed of 112 and gamma 0*8 for six 

 minutes development in an ordinary pyro-soda developer 

 at 17° C. The average size of the grain is about 09yit 

 diameter. 



The method of preparation of strips for sensitometric 

 exposure is, briefly, as follows : — One 5 in. x 7 in. plate of the 

 original emulsion is soaked in distilled water for one half-hour 

 at 0° C. to 8° C. (All work for sensitometric exposure was 

 done in a dark room by the aid of a dull red safelight, 

 Wratten Series 2). The water is removed and a warm 

 solution of gelatine, alcohol, and water is added and the 

 whole solution heated in an oven for 20 minutes, while care 

 is being taken not to heat over 10° C, because above this 

 temperature much fogging takes place. With several such 

 applications of the aforesaid solution the emulsion is entirely 

 removed from the plate and the resulting solution made up 

 to such a volume that it will give one layer of grains upon 

 coating and drying. Some of the slides are used at once to 

 get the clump frequency data. Those for exposure are 

 backed with an opaque substance to prevent reflexions, then 

 exposed in a sensitometer, developed to gamma infinity with 

 a pyro-soda developer at 17° C, washed, and the developed 

 silver removed with a dilute solution of chromic acid and 



