Proceedings of the Society of Arts. 419 



The process was exhibited, and specimens were produced by means of 

 the Oxy-hydrogen Light. (632.) 



Dr Fyfe made a few remarks on the properties of the compounds of 

 silver, more particularly their being darkened by the action of light ; so 

 that paper besmeared with them, and exposed to light, becomes dark 

 coloured. Hence the process of photogenic drawing. The compound 

 employed by Mr Talbot is the Chlorid, but Dr Fyfe stated that he pre- 

 ferred the Phosphate, not only because it is extremely sensible to light, 

 but also because it is applied more easily and uniformly to the paper. It 

 gives a pale yellow tinge, so that it is thus easily known when the paper 

 is equally spread over with it. The proportions he recommends are, a 

 saturated solution of phosphate of soda, diluted with three, or sometimes 

 four of water, and a solution of Lunar Caustic, diluted with six of water, 

 the phosphate being first applied. Instead of these solutions, he some- 

 times besmears the paper with phosphate of silver, suspended in water, 

 to which a little mucilage is added. Paper thus prepared is equally sen- 

 sitive as that with the chlorid. Specimens of impressions taken from dried 

 plants, from engravings, and from landscapes on glass, both on chlorid 

 and phosphate paper, were then exhibited. Dr Fyfe next made a few 

 remarks on the means recommended for preserving the impressions. He 

 stated that he had failed in preserving them by the use of sea-salt, as re- 

 commended by Mr Talbot, and that as to the iodide of potassium, also re- 

 commended by him, he had found great difficulty in applying it success- 

 fully, owing to the ease with which it acts on the shaded part of the im- 

 pression. This had induced him to try the preservation by preventing 

 the transmission of that part of the solar ray which causes the blackening. 

 This he attempted by covering the paper with a red or yellow colour. In 

 some trials which he had made, he had so far succeeded that impressions 

 covered with a faint tinge, by chrome yellow, had resisted the action of 

 light. One of these he exhibited, which had been hung up for two days 

 opposite the windows of a room with a south exposure, and another 

 which had been exposed at a window for several hours, during two or 

 three of which the sun was pouring its rays on the paper. In both of these 

 the impression seemed to be little, if at all, affected. Dr Fyfe stated that 

 he had great hopes that this method might be applied successfully in pre- 

 serving the impressions. It was also mentioned that the light of the oxy- 

 hydrogen blowpipe was sufficiently intense to produce the impressions, 

 and after finishing his remarks, he shewed the method of doing so. A 

 small dried leaf of the wild geranium was used, by which, in seven 

 minutes, a distinct representation of the leaf was produced. Dr F^fe also 

 read a letter from Mr Dunn, the Curator, stating that he had that day 

 succeeded in procuring an impression of a section of a piece of cane, by 

 means of tlie solar microscope. The impression, which was on phosphate 

 paper, was exhibited. Thanks given to Dr Fyfe from the Chair. 



4. The Report of the Experimental Committee on Dr Traill's Indeli- 



