870 M. C. Lea—Sensitiveness to Light of Salts of Silver. 



The silver compounds which exhibit the greatest tendency 

 aent images by the action of light are of course the 

 Qide,*ndeh]orida But the same tendency is shared 

 degree by other compounds, and the latent image 



receive latent images, developable by a precipitate in the act 

 of formation, was examined many years ago by Mr. Eobert 

 Hunt. Since then the matter has received but little attention, 

 and if I am not mistaken, no investigations have at any time 

 been made as to the capacity of silver salts other tha 

 bromide, and chloride to receive latent images of the second 

 sort, viz: those susceptible of alkaline development, in the en- 

 tire absence of silver nitrate. This subject I have recently 

 examined with the following results : 



Soluble salts of acids capable of forming insoluble or nearly 

 insoluble salts with silver were selected and the surface of very 

 pure paper was impregnated with them. After drying, the 

 ire floated on a solution of silver nitrate, containing 

 about twenty grams to the ounce, acidulated with half a drop 

 •id, sp. gr. 1-28 to the ounce of solution. The excess 

 of silver nitrate was then washed out. One set of papers were 

 then simply dried, another set were soaked for about a minute 

 in a ten grain solution of gallo-tannic acid, and then again washed. 

 The salts thus' formed on the surface of the paper were ex- 

 posed to a strong diffuse light for, in some cases, twelve seconds, 

 in others, seven. They were then submitted to the action of a 

 very weak solution of pyrogallol, ammonium carbonate and 

 potassium bromide, the latter used to check the rapidity of the 

 action of the other agents. 



Silver citrate and tartrate both gave rather weak images. The 

 citrate showed a strong tendency to irregular reduction. 

 Nothing of this appeared in the case of the tartrate. 



- s " v - '" r^atinwjanifle gave quite a strong image, stronger than 

 any other substance tried, except of course the silver bromide 

 used for comparison. 



Silver mucate gave a very faint image with much irregular 

 reduction. 



>;;;■ r pyrophosphate behaved in the same way. 

 lS ' ''"•/"'- ''•* <ruve a moderately strong image, coming next 

 to the platmocyanide, and like it, clear and free from all irregu- 

 lar reduction. 



_ Silver snlp}iocya,;.Me, an extremely faint image with much 

 luction. 



irregular 



weak image entirely free from 



ck-ar. 



Silver fulminurate, weaker than the last mentioned, 



