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IX. 



ON THE CONDITIONS OF EQUILIBRIUM OF DELIQUESCENT AND HYGRO- 

 SCOPIC SALTS OF COPPER, COBALT, AND NICKEL, WITH RESPECT 

 TO ATMOSPHERIC MOISTURE. By W. N. HARTLEY, F.R.S., Honorary 

 Fellow of King's College, London ; Professor of Chemistry, Royal College of Science, 

 Dublin. (Plates XXIIL, XXIV., and XXV.) 



[Read Mabch 20, 1901.] 



In two published papers I have described some remarkable chano-es in colour 

 which are seen on dissolving pure and neutral crystallized salts in water, and on 

 dilution of their saturated solutions with water.* The behaviour of cupric 

 bromide was described ; and the conclusion was drawn that both the chloride and 

 bromide, with two and five molecules of water, respectively undergo partial de- 

 hydration when concentrated solutions are prepared at 60" F. 



These conclusions appear to have been justified and confirmed by the 

 following experiments, which were made with the object of ascertaining the 

 conditions of equilibrium under ordinary atmospheric changes which govern 

 the formation of hydrates of the hygroscopic and deliquescent haloid salts of 

 copper, cobalt, and nickel. 



Method of Experimenting. 



A large bell-jar was placed on three blocks of wood an inch in thickness, and 

 within the jar were six beakers, one of which contained distilled water. The 

 other five were each weighed empty, and weighed again after adding a small 

 quantity of one of the salts to be examined. Inside the jar dry and wet bulb 

 thermometers were placed to determine the tension of aqueous va2)our, and 

 outside was a Six's maximum and minimum thermometer. 



Every day, at as nearly as could be the same hour, the thermometer readings 

 were recorded in the following manner : — 



The pressure of aqueous vajjour was found from the difference between the 

 wet and dry bulb thermometers by reference to Glaisher's hygrometic tables. 



*Jourii. Chem. Soc. of London, vol. xxviii., 1875, p. 206; Sci. Trans. Roy. Dublin Soc, vol. %'ii. 

 ser. 11, 1900, pp. 253-312. 



TRANS. KOY. DUB. SCO., N.S. VOL. VII., PAET IX, 2 X 



