132 ANNUAL OF SCIENTIFIC DISCOVERY. 



concentrated solution, formed of equal parts of ferrocyanide of 

 potassium and nitrate of lt>ad, havin<; found tlio latter to answer 

 ver\' ^vt']\, not only as a means of fonnini; a jireeipitate, but also 

 for assistinji^ in tiie production of numerous colors. After dryinj^ 

 the paper, it. was exposed to the sun for about lialf an hour, and 

 then washed in water in order to dissolve all the unaffected fer- 

 rocyaniile of potassium and nitrate of lead. I have notii-cd that 

 the sun acts much tjuicker when there is a little moisture present. 

 I have, therefore, placed a damp cloth between two or three 

 thicknesses of jiaper ijchind the prciiarctl paper. After washing, 

 tht^ photographic iinai^t; remains Itchind as a pale g'reenish pre- 

 cipitate, easily transformed into the various colors, as the follow- 

 ing experiments will show: — 



" No. 1. (Ulue.) Has been steeped in a weak solution of nitrate 

 of iron for about ten minutes, and then wasiied in water. 



"No. 2. (tireen.) Same as No. 1, but steeped in a weak solu- 

 tion of bichromate of potash alter the nitrate of iron. 



" No. 3. (Reddish lirown.) Has been steeped in a solution of 

 nitrate of ecjpper, and then washed. 



"No. 4. (Brown.) Has been developed by steeping it in a 

 mixture of weak solution of nitrate of iron and nitrate of copper. 



" No. 5. (Dark Brown.) Has ahso been treated with a solution 

 of nitrate of iron and nitrate of copper, but containing a larger 

 pro])ortion of the former. 



"Tiiese few experiments will show that a very large number 

 of shades may be oljtained by using diiferent salts an(l mixtui'es 

 thereof in develojnng the photograph. A further series of colors 

 may be oljtained i)y destro} ing the blue with caustic-soda, which, 

 after washing, will leave Ijchind oxides of iron and lead, which 

 may be dyed with vegetable coloring matters. 



"All the al)ove exj)crimcnts were made about four years ago, 

 which goes to prove that the colors are permanent. I hope 

 shortly to be able to resume my experiments, and work the 

 process out more perfectly." 



COLORED PICTURES BY THOTOGKArHY. 



In 1838, Herschel was the first to publish a paper on the various 

 colors which chloride of silver is susceptible of taking under the 

 influence of certain colored rays (;f light. ]\Ir. Robert Hunt also 

 publi?lied,in 1840, a paper referring to the subject; but the most 

 complete series of researches on the subject of the i-eproduction 

 of the colors of the spectrum, and which led to a process by 

 which several of the colors of the spectrum could be pi'oduced 

 on a sensitive surface, is due to Edmund Becquerel. The results 

 arrived at by this gentleman Avere so remarkable that they drew 

 the attention of the whole scientific world ; and the following is an 

 outline of the processes which were applied by him to obtain this 

 interesting result. He took a daguen-eotype plate, or a silver-plated 

 one, and having dipped it in a weak solution of chlorine, or, what 

 was still better, a weak solution of hydrochloric acid, by connecting 

 it with the poles of a battery, the brilliant sUver surface acquii'ed 



