350 THE BEGINNIISIGS OF PHOTOGRAPHY. 



in coiit'orniitv with Schcele's ob,scr\;iti()ii that hydrochloric ucid was 

 found in the water after oxpo.surc of the clilori(Ui to light. (Essai de 

 Stati(iue Ciiinii(|iie, ISOo.) He also found that the ])lackened chloride 

 dissolved in annnonia as well as the white and was unchanged. There 

 was, therefore, no disenoagemeut of oxygen from the chloride, tlie 

 gas l)ul)l)les noticed being due to air adhering to it. This was further 

 proved by melting some ])lackened chloride in a retort, as Avell as ])y 

 exposing some Avhite chloride to a moderate heat till it blackened 

 before melting. In both cases hydrochloric acid was evolved, but no 

 oxj'gen. It appears, therefore, that light sim})ly ))rings a)>out the 

 separation of a portion of the h3alrochloric acid coml)ined with the 

 silver, and the same effect can l)e produced })y heat. Another portion 

 of white chloride set in a dark place in a current of air darkened 

 almost as ({uickly as if light had acted upon it. The air, therefore, 

 had caused the disengagement of part of the hydrochloric acid, which 

 must escape if the chloride blackens, and this result can l)e brought 

 about in Aarious ways. We ma}^ note that Stahl (Anweisung zur 

 Metallurgie, 1720) mentions this remarka))le volatility of the precipi- 

 tated chloride and its visible fuming and loss of substance when 

 exposed to a strong current of air. In another work he also notes the 

 darkening and volatilization of luna cornea when heated with access 

 of air, and attributes the change of color to the action of sulphur. 



Some experiments by the Abbe A. M. Vassali, described in two 

 papers entitled "Parailele de la Lumiere Solaire avec celle du Feu 

 comumn," published in Vol. V of the Memoirs of the Turin Academy 

 (1791-92), may be noticed. He shows that precipitated silver chloride 

 can be darkened, though slowly, bv the flame of a lamp as well as by 

 solar rays; also that it could be slightl}^ darkened by the light of the 

 full moon, especially if it were concentrated ])y a lens. (This result 

 was disputed ))}' subsequent observers.) He concludes, therefore, that 

 the light of the moon is the same as that of a flame or of sunlight, but 

 not so intense. He used the chloride taken moist from a bottle and 

 spread on unsized paper. In the second paper, he describes an experi- 

 ment made to ascertain the loss of weight in the dr}^ chloride after 

 exposure to light, and how on concentrating the sunlight with a lens 

 the chloride was partly reduced to metal. 



MRS. FULIIAME. 



More closely connected with photograph}- is the work of Mrs. Ful- 

 hame, as desci'ibed in her book. An Essay on Cond)ustion, with a view 

 to a new Art of Dying and Painting, etc. (1794). She began her 

 experiments in 1780 in making cloths of gold, silver, and otiier metals 

 by chemical i)rocesses. She also prepared maps in which the I'ivers 

 were shown in silver and the towns, etc., in gold, and it is evident 



