Af. a Lea— Sensitiveness of Silver Br 



the coloring matters had been applied. Comple 

 " e, and the exposure m 



I sunlight, in winter, the exposure was 

 about 45 seconds, corresponding to perhaps 20 or less of summer 

 light The development was in'ali cases the alkaline, viz : pyro- 

 gallol, and ammonium carbonate controlled with potassium 

 bromide. 



As already said, the main object of the research was to arrive 

 at a solution of the question whether any red pigment could be 

 found which would enhance sensibility to the green rays. The 

 following were tried : 



Ammonium hsemateate. Murexide. 



Santaline. Aurine. 



Coralline. Carminic acid. 



Rosaniline. Naphthaline red. 



Ferric sulphocyanide. 

 In addition to these substances of well-established composi- 

 tion, some pigments were tried whose commercial names are : 



Cardinal red. Rouge ponceau. 



Saifranine. Bordeaux claret. 



With the single exception of coralline, not one of these sub- 

 stances produced the slightest increase of sensitiveness to the 

 green rays. 



It was my intention, in the case of finding any red pigments 

 which increased the sensitiveness to green light, to make a care- 

 ful study of their absorption spectra by means of the spectro- 

 scope, but as none such were found except coralline, its spectrum 

 only was examined. 



The power of coralline, however, to increase the sensitiveness 

 of AgBr, to green light, cannot be considered as any function 

 of its color, for two most excellent reasons. 



1. Coralline exhibits a still more marked tendency/ to increase the 

 sensitiveness of AgBr to the red ray than to the green. This action 

 on the red ray was observed and published by me in March, 

 1875, and completely disproves of the theory of any special 

 action of coralline upon the green ray. There appears to be a 

 heightening of sensibility to the less refrangible end of the spec- 

 trum, rather than to any particular ray. 



2. The action on green light is not a function of the color ot 

 coralline, because it is easy to destroy that action without destroying 

 the color. This singular result is accomplished in the following 



Coralline appears to be the ammonia salt of a yellow acid. 

 If we place a drop or two of a weak acid, acetic or gallic, m a 

 capsule, and add a few drops of alcoholic solution of coralline, 



