PHOTOGRAPHY, SCIENTIFIC ASPECTS 



graphs with a solution of gold, greatly increasing the 

 richness of their tones. There were, besides these 

 important discoveries, a number of minor ones that 

 helped in developing the process. But still it was too 

 complicated for anyone, other than a trained scientist, 

 to attempt successfully was, indeed, still in the experi- 

 mental stage, and of little account commercially. But 

 just before the century turned the half-way point, 

 another important discovery was made which placed 

 practical photography within the grasp of any ordinarily 

 intelligent operator, even one without any special 

 scientific training. 



GLASS NEGATIVES 



This discovery, or invention, was that of the now fa- 

 miliar glass negative, from which prints could be made. 

 The inventor was Niepce St. Victor, a nephew of Da- 

 guerre's partner, who had been trained by his uncle, and 

 who had continued the investigations begun by the 

 elder Niepce. In his experiments he used glass plates 

 sensitized by iodized albumen, and obtained fairly satis- 

 factory results; but this process was soon improved by 

 Blanquart and Le Gray. The essential part of their 

 process consisted in treating a glass plate with a mix- 

 ture of the whites of eggs containing potassium iodide 

 and potassium bromide. This solution was first dried on 

 the plates, and was then sensitized by treatment for a 

 few minutes with a solution of nitrate of silver. Such 

 plates were exposed to the camera image while still wet, 

 and then developed in a gallic- acid solution. They were 



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