466 Chronicles of Science. [July, 



having been exposed to direct sunlight for eight months. M. Graf- 

 field, of Botson, U. S., who has been for more than twenty years in 

 the wholesale glass trade, and is at the same time a good observer, 

 has recently sent to the Photographic Society of Marseilles a series 

 of the results of his researches and observations on this subject, in 

 which he comes to the conclusion (which is especially important to 

 photographers) that glass is even sensibly affected after one single 

 day's exposure to the sun's rays, and that all glass, wathout excep- 

 tion, including that used for optical purposes, is more or less acted 

 upon, even when made from the best materials and by most ex- 

 perienced workmen ; greenish glass seems to become the least affected. 

 The author has sent to Marseilles a series of photograjDhs representing 

 the tinge and changes produced in divers varieties and kinds of glass 

 after exposing them to sunlight. 



Many of our readers have had the opportunity of noticing that 

 bottles, especially if made of white glass, containing disulphide 

 of carbon often become lined, if exposed for any length of time 

 to direct sunlight, with a coating strongly adhering to the glass. 

 M. Loew has experimented on this substance, by enclosing the disul- 

 j^hide in sealed glass tubes previously moistened with water, which 

 has the effect of lessening the adhesiveness of the brownish coating. 

 On opening the sealed tubes after a few months' exposure to sun- 

 light, the water was observed to have an acid reaction, due to the 

 formation of some formic acid. The solid substance alluded to is 

 insoluble in alcohol, chloroform, ether, and disulphide of carbon, but 

 soluble in a boiling solution of caustic potassa, becoming, however, 

 at the same time decomposed. It has the composition of sesqui- 

 sulphide of carbon, and on being submitted to distillation is decom- 

 posed, yielding sulphur and carbon. The disulphide of carbon 

 from which this substance is deposited contains sulphur in solution, 

 although it was perfectly pure previous to exposure to sunlight. 



When freshly-precipitated chloride of silver (best obtained by 

 decomposing a soluble silver salt with chlorine-water) is placed 

 in a white-glass tube about 15 inches in length, and exposed to 

 the action of direct sunhght, it will be observed that the chloride 

 of silver remains quite white as long as the solution of cLlorine- 

 water retains its greenish-yeUow colour ; but as soon as that colour 

 has vanished, the chloride of silver begins to decompose water under 

 the influence of the direct rays of sunlight ; the chloride gradually 

 blackens, and after a shorter or longer duration of time, the whole 

 quantity will have become black, especially if care be taken to shake 

 tlu! tube now and then, so as to expose the whole mass to the light. 

 When the tube is afterwards placed in a dark ])lace, entirely 

 excluded from dayhght, the black colour of the chloride of silver 

 again disappears gradually, and the cliloride becomes Nvhite. This 



