128 ANNUAL OF SCIENTIFIC DISCOVERY. 



ment as will determine the reflection of yellow light, and so of the other 

 rays. In fact, in 1840, Sir John Herschcl published an account of 

 some experiments in which the production of color was very evident ; 

 and on paper prepared with a brown vegetable juice, he obtained an 

 impression of the spectrum, colored from end to end, the color of each 

 ray being impressed in the natural order. To Becquerel, is, however, 

 certainly due. the discovery of the mode of preparing a metallic plate 

 in such a manner as to produce a tablet susceptible of chromatic im- 

 pressions. This was effected about two years since ; his process con- 

 sisting essentially in the formation of chloride of silver, or probably 

 of a sub-chloride, upon a metal plate. In the camera-obscura, highly 

 colored images were copied, and the copies gave colors of a natural 

 character. In this way, however, only large masses of color, as the 

 colors of a geographical map, were copied, and impressions of the spec- 

 trum obtained. 



The memoir of M. Nicpce, before the French Academy, is entitled, 

 " The relation existing between the colors of certain colored flames, 

 with the Heliographic images colored by light." 



When a plate of silver is plunged into a solution of sulphate of cop- 

 per and chloride of sodium at the same time that it is rendered electro- 

 positive by means of the voltaic battery, the chloride formed becomes 

 susceptible of coloration, when, having been withdrawn from the bath, 

 it receives the influence of light. This was the discovery of Becquerel. 

 M. Niepce had been led to think that a relation existed between the 

 color communicated by a body to a flame, and the color developed upon 

 a plate of silver, which should have been chloridated with the body 

 which colors this flame. The bath in which the plate of silver was 

 plunged, was formed of water saturated with chlorine, to which was 

 added a chloride possessing the property of coloring flame. 



It is well known that strontian gives a purple color to flames in gen- 

 eral, and to that of alcohol in particular. If we prepare a plate of silver 

 and pass it into water saturated with chlorine, to which is added some 

 chloride of strontian, and when thus prepared we place upon it a colored 

 design, of red and other colors, and then expose it to the sunshine, after 

 six or seven minutes we shall perceive that the colors of the image are 

 reproduced upon the plate, but the reds much more decidedly than the 

 others. When we would produce successfully the other rays of the 

 solar spectrum, we operate in the same manner we have indicated for 

 the red ray, employing for the orange the chloride of calcium, or that 

 of uranium for the yellow, or hypochlorite of soda, or the chloride of 

 sodium and potassium. If we plunge a plate of silver in the chlorine 

 liquid, or if we expose the plate to the vapor, we obtain all the colors 

 by the light, but the yellow only with any degree of veracity. Very 

 fine yellows have been obtained with a bath composed of water slightly 

 acidulated with hydrochloric acid with a salt of copper. The green 

 rays are obtained with boracicacid, or the chloride of nickel ; also with 

 all the salts of copper. The blue rays are obtained with the double 

 chloride of copper and ammonia. Indigo rays are obtained with the 

 same. The violet rays arc- obtained with the chloride of strontia and 

 the sulpnate of copper. 



