Proceedings of the Photogbaphical Section. 1075 



belong to the same type, distinguisbed as the water type, and are 

 designated by the following symbols : 



O and [0 



H ) Ag. 



in which the atomic weight of oxygen is doubled, that is = 16. 

 To those who have been chemically educated under the old system, 

 it may be well to explain that the nitrogen atom being a triad, and 

 two atoms of the dyad oxygen, having the same quantivalence as a 

 tetrad, the saturating power oT ISTOg, is the difference between a 

 triad and a tetrad, that is, 4 — 3=1. An atom of silver, expressed 

 by Ag, being a monad, it will be seen that the atomicity of the atoms 

 included in the second bracket is virtually that of the atoms included 

 in the first bracket of the^ first named symbols. For reasons which 

 need not be here givei), I prefer not to recognize the hypothetical 

 compound ammonium, and to show the combination of the bodies 

 represented in the first named symbols, which is said to produce a 

 body having alkaline characteristics, I would arrange them after the 

 double water type, thus : 



NO, 



O, 



II 

 . H 



Ag. j 



Finally, it may be observed that a change in chemical structure does 

 not necessarily involve a change in chemical functions ; but the 

 tj^pical formula expresses more clearly the new part which, it is now 

 supposed, may be played by silver, and which, if confirmed by 

 further experiments, will become the starting-point in a new series 

 of discoveries. 



Mr. Chapman said he had not been able to detect any increase of 

 sensitizing in the alkaline solution. He expressed doubts of such 

 solution proving any more sensitive than a new slightly acid solution 

 made from the same sample of silver crystals. 



In answer to a question by Mr. Chapman, the chairman stated, 

 that a solution made alkaline by ammonia, would be more likely to 

 change or loose its alkaline condition than one in which one of the 

 metallic alkalies had been used. 



Mr. Kurtz exhibited a model of concave backgrounds, and explained 

 the method of using the same. He also exhibited several very fine 

 negatives and prints from the same. 



