5^ REPORT 1856. 



best identified by boiling tlie coated foil in a weak and faintly alkaline solution of 

 permanganate of potash, until the whole of the liquid is destroyed, filtering, acidi- 

 fying the filtrate, and treating it with sulphydric acid, when the cliaracteristic orange- 

 coloured antimonial sulphide is produced. 



On the Compounds of Chromium and Bismuth. By W. R. Pearson. 



On Engraving Collodion Photographs by means of Fluoric Acid Gas. 

 By Charles Pooley, Cirencester. 

 In this paper the author set forth the means he had adopted in order to obtain 

 engraved impressions of collodion photographs on glass. He divided the process into 

 four steps : — 



1 St. The preparation of the plate. 

 2nd. The treatment of the picture. 

 3rd. The application of heat to the picture. 



4th. The exposure of the picture to the influence of fluoric acid gas. 

 In the preparation of the plate, Mr. Pooley found it necessary to use new glass, 

 and strong collodion well iodized, and also to deposit as much pure silver as possible, 

 for which purpose he developed with protosulphate of iron and acetic acid, although 

 be thought other agents would answer the purpose equally well. 



The author tlien proceeded to show that the gi-eat obstacle he had to contend with, 

 was the presence of the film of collodion covering the glass; but this was overcome 

 by submitting the plate to a high temperature, which gave to the silver a white, frosted 

 appearance, and attenuated the film of collodion so much as to make it permeable to 

 the action of the gas. The picture was then exposed to the influence of the dry, 

 warm vapour of fluoric acid, and in 20 to 40 seconds the operation was completed. 



Having washed off the film, a fine etching becomes visible, so delicate in its mark- 

 ings, and yet so perfect, that the unassisted eye is unable to discern all its beauties. 

 It requires a lens to make out all the minutije of detail correctly. 



The author then adverted to a remarkable fact which he had observed in the 

 character of the engraved picture, namely, that the portions of the glass on which the 

 silver had been deposited were those on which the action of the gas first took place, 

 the vmsilvered parts being imafFected by it. This circumstance, which appears to be 

 at variance with our notions of the ancient claims of fluoric acid for silica, opens a 

 new field for investigation. The author refrained from offering an explanation of 

 this interesting question, but left it as a subject for future consideration. 



On the Gases of the Grotto del Cave. 

 Bij the Rev. C. Pritchard, WI.A., F.R.S. 



the Corrosive Action of Smoke on Building Stones. 

 By Professor A. Voelcker, Ph.D., F.C.S. 



On the Composition of American Phosphate of Lime. 

 By Professor A. Voelcker, Ph.D., F.C.S. 



On Basic Phosphates of Lime. By Professor A. Voelcker, Ph.D., F.C.S. 



On Albuminized Collodion. By W. Sykes Ward, F.CS. 

 Immediately after the publication of M. Taupenot's process, I proceeded to experi- 

 ment on it, under the impression that it possessed many advantages over the dry 

 photographic processes then known, and that the further investigation of it was likely 

 to lead to results of the highest interest, both practically and theoretically. In these 

 respects I have not been disappointed, and I can most decidedly recommend the 

 adoption of the process to all photographers, as well to those who are not afraid of a 

 little trouble in the manipulation of preparing their own materials and plates, as to 

 those who, preferring the artistic choice of subjects, would rather commit the prepara- 

 tion and subsequent development of plates to assistants, or to professional photographers. 



