HISTORY OB^ PHOTOGRAPHY. 177 



violet is of a rich blue color, which it imparts iu high perfection to paper. 

 Exposed to sunshine, a portion of this color gives way pretty readily, hut a 

 residual blue, rather inclining to greenish, resists obstinately and requires a 

 very much longer exposure (for whole weeks, indeed) for its destruction, which is 

 not even then complete. I'hotographic impressions, therefore, taken on this 

 paper, though very pretty, arc exceedingly tedious in their pre])arati()n if we 

 would have the lights sharply made out. 



^^l>(lraJ■is tricolor?, var. — t^timiilat'uig effects of allcalies. — Among a great many 

 hybrid varieties of this genus, lately forwarded to me from the Cape, occurred 

 one of a very intense purplish brown color, nearly black. The alcoholic extract 

 of this flower in its liquid state is rich crimson brown. Spread on paper, it 

 imparted a dark olive-green color, which proved perfectly insensible to very 

 prolonged action, either of sunshine or the spectrum. The addition of carbonate 

 of soda changed the color of this tincture to a good green, slightly inclining to 

 olive, and which imparted the same tint to paper. In this state, to my sur- 

 prise, it manifested rather a high degree of photographic sensibility, and gave 

 very pretty pictures with a day or two of exposure to sunshine. When pre- 

 pared with the fresh juice there is hardly any residual tint, but if the paper be 

 kept a great amount of indestructible yellow remains outstanding. The action 

 is confined chiefly to the negative end of the spectrum ; all but the first five or 

 six parts beyond the yellow show little more than a trace of action. A photo- 

 graph impressed on this paper is reddened by muriatic acid fumes. If then 

 transferred to an atmosphere of ammonia, and when supersaturated the excess 

 of alkali allowed to exhale, it is fixed, and of a dark-green color. Both the tint 

 and sharpness of the i)icture, however, suft'er in this process. 



Red popiiij: Papiirer Rheuut?. — Among the vegetable colors totally destroyed 

 by light, or which leave no residual tint, at least when fresh prepared, ijerhaps 

 the two most rich and beautiful are those of the red poppy and the double purple 

 groundsel (Scnecio spleiidciis). The former owes its red color in all proba- 

 bility to free carbonic acid or some other, as the acetic, completely expelled by 

 drying, for the color its tincture imparts to paper, instead of red is a fine blue, 

 very slightly verging on slate blue. But it has by no means the ordinary 

 chemical characters of blue vegetable colors. Carbonate of soda, for instance, 

 does not in the least degree turn the expressed juice green, and when washed 

 with the mixture a paper results of a light slate gray, hardly at all inclining to 

 green. The blue tincture is considerably sensitive, and from the richness of its 

 tone and the absence of residual tint, paper stained with it affords photographic 

 impressions of great beauty and sharpness, some of which will be found among 

 the collection submitted with this paper for inspection. 



Setiecio splemlens. — This flower yields a rich purple juice in great abundance 

 and of surprising intensity. Nothing can exceed the rich and velvety tint of 

 jiaper tinted while it is fresh. It is, liowever, not very sensible to light, and 

 many w(>eks are necessary to obtain a good photographic impression. 



In the progress of my OAvn researches on this subject I found that 

 the oreen coloring- matter of the leaves of herbaceous plants when 

 spread upon 2)aper changed with tolerable rapidity when exposed to 

 sunshine. There are, however, some very curious points connected 

 with the phenomena of these changes which demand a far more ex- 

 tensive investigation than they have yet received. 



I find that the juices taken from the leaves in the spring change 

 more rapidly than when expressed from the same plants in the 



