1869.] Chemistry. 429 



so much common salt as will cause a whitish-coloured precipitate. 

 When it is desired to apply this mixture for platinizing, the objects 

 to be treated are placed in a vessel made of zinc and perforated 

 with holes ; the vessel is then placed, with its contents, for a few 

 seconds in the mixture just described, which, just previous to using, 

 should be heated to 60° C. On being removed from the zinc 

 vessel, the objects are to be washed with water and dried in saw- 

 dust. 



Professor Nickles calls attention to the fact, that when chloride 

 of sulphur of commerce is mixed with sulphide of carbon wheriin 

 phosphorus has been previously dissolved, a fluid is formed, which, 

 though emitting fumes when in contact with air, is harmless, and 

 may be for any length of time kept in well-stoppered bottles ; on 

 addition of liquid ammonia, however, or on passing into this liquid 

 a few bubbles of ammonia gas, a most intense combustion at once 

 ensues. This is due to the fact that the ammonia seizes upon the 

 chloride of sulphur, forming cliloride of ammonium, whereby so 

 much heat is set free as to cause the combustion of the sulphide of 

 carbon and phosphorus dissolved in it. 



Pkoceedings of the Chemical Society. 



On Thursday, March 4, 1869, Mr. Tomhnson read his long- 

 promised lecture " On Catharism, or the Influence of Chemically 

 Clean Surfaces." He explained the sense in which he applied the 

 new term, catharism (from Kabapog, 'pure or clean), distinguishing 

 between " clean " in its ordinary and in its chemical sense. The 

 finger could not be made chemically clean by any process, whereas 

 a glass rod, cleansed with strong acids or alkalies, and well washed, 

 was chemically clean, and no longer possessed the power of liberat- 

 ing either salt or vapour from liquids. The action of solid bodies 

 in determining these changes he ascribes to the greasy film which, 

 after exposure to the air, they are sure to acquire. For this film, 

 the adhesion of the solid or vapour is greater than it is for the glass, 

 and hence the efiect of the solid. To such chemical uncleanness 

 all phenomena of this kind should, he thinks, be ascribed, and he 

 defines a nucleus as a body which " has a stronger adhesion for 

 the gas, or the salt or the vapour of a solution, than for the liquid 

 which holds it in solution." He rej)udiates the notion that tempe- 

 rature has anything to do with the phenomena of supersaturation, 

 and describes experiments in which supersaturated solutions of 

 various salts were kept for hours in catharized vessels at a tempera- 

 ture of 10° Fahr. without crystallization taking place. This was. 

 even observed with alum, which does not usually exhibit this pecu- 

 liarity. The views of Ldwel on crystalhzation and the phenomena 



2 G 2 



