34 report — 1865. 



he due to the extinction of light by the absorbing action of the crystal on one of 

 the polarized beams. 



A few words on Sponges as a Source of Bromine and of Nitrogen. 



By Dr. Phipson. 



On the Sublimed Oligist of Vesuvius, and its Artificial Production. 

 By Dr. Phipson. 



On Silicium in Iron. By Dr. Phipson. 



On the Action of Light \ipon Sulphide of Lead, and its bearing upon the Pre- 

 servation of Paintings in Picture Galleries. By Dr. D. S. Price, F.C.S. 

 The author's attention was directed to this subject by observing that in the cases 

 in the Technological Museum under his charge at the Crystal Palace, which are 

 painted with white-lead, substances which emitted sulphurous vapours did not 

 cause a darkening of the surface of the case, excepting where it was protected from 

 the direct influence of light. A number of experiments was then tried as to the action 

 of light upon sulphide of lead produced by the action of sulphuretted hydrogen on 

 lead paint. A board painted white with white-lead was exposed for several hours 

 to the action of sulphuretted hydrogen, untd the surface had acquired a uniform 

 brown colour. Plates of glass of different colours were then placed upon the painted 

 surface, one portion being at the same time covered with an opaque medium, and 

 another left entirely exposed. The board was then placed facing the light. The 

 glasses employed were red, blue, yellow (silver), violet, and smoke-colour glass. The 

 results exhibited were after an exposure of eight days, and showed that the parts of 

 the board directly exposed to light were bleached ; those protected by an opaque 

 medium were not acted upon, while with the glasses of different colours interme- 

 diate effects were produced, those of the blue glass being most decided. Drying- 

 oils in conjunction with light rapidly bleach sulphide of lead, and boiled oil effects 

 the bleaching still more rapidly. When water-colour is used bleaching takes place, 

 but much more slowly than in the case of oil. After quoting authorities, stating that 

 generally light was advantageous to\he preservation of pictures, Dr. Price showed a 

 striking illustration of this fact. He had a picture painted, and then exposed it to 

 the action of sulphuretted hydrogen, until it became sadly discoloured, and to all 

 appearance destroyed. Some strips of paper were laid across the picture so as to 

 cover some parts. The picture, thus partially covered, was exposed to light for a 

 long time. The result, as shown at the Meeting, was curious indeed — the parts of the 

 picture exposed being perfectly restored, while those protected by the paper re- 

 mained still discoloured. From his experiments he came to the conclusion that it 

 was advantageous to have picture-galleries well lighted, especially where, as in 

 towns, the atmosphere was charged with sulphur compounds, and that it was quite 

 a mistake to have curtains placed in front of pictures with a, view to their protec- 

 tion. In the course of his communication, Dr. Price stated that it was curious to 

 observe in many parts of London the discoloration of houses painted with white 

 lead. He had frequently seen the lower portions completely coated with a metallic- 

 like surface of the sulphide, and had little doubt that the formation of this com- 

 pound w T ould be found to be more frequent in winter than in summer, and more 

 prevalent on the shady than on the sunny side of a street. 



The Progress of the Manufacture of Gun- Cotton, and its application to Mining, 

 Military, and Sporting Purposes. By Manning Prentice. 



On the Properties of ParTcesine, and its Application to the Arts, Manufactures, 



and Telegraphy. By Owen Rowland. 



Parkesine is so called after its inventor, Mr. Alexander Parkes, of Birmingham, 



the well-known discoverer of the cold process of vulcanization of Indian rubber. 



This material is suitable for a great variety of purposes, possessing properties kin- 



