128 



Dr. T. Ewan. On the 

 Fia. 3. 



500 



'250 



710 



C 610 I) E 5| 



Extinction coefficients of water. 



6 410 



and again in the neighbourhood of D, corresponding to the two 

 absorption bands which have been described by several authors.* It 

 is also noticeable that the absorption slightly increases in the violet 

 near G. 



Solutions of Cupric Salts. 



The salts used were cupric sulphate, nitrate, chloride, bromide, and 

 acetate. They were purified carefully, notwithstanding which the 

 solutions made by dissolving them in water were not sufficiently clear 

 to be measured. Filtration through fine Swedish filter paper only 

 improved them a little. The desired freedom from suspended par- 

 ticles was, however, easily obtained by nitration through porous 

 earthenware. The apparatus shown in fig. 4 was found to be very con- 

 venient, as it allowed of two or three litres of a solution being filtered 

 without requiring any attention. A and B are ordinary Winchester 

 quart bottles, C is the " Chamberland Pasteur candle.'' The solution 

 to be filtered is contained in A. B is evacuated, and the apparatus 

 left to itself till the solution has filtered. Two litres could be filtered 

 in an hour, or less if a good vacuum was kept up. 



The solutions measured were always analysed as the filtration 

 changes their concentration somewhat. Two methods of analysis 

 were used, and the mean result taken. 



* Sclionn, < Pogg. Ann. Ergz.,' 8, p. 670, 1878; Eussel and Sapraik, < Nature,' 22, 

 p. 368, 1880; and Soret and Sarasin, 'Arch, de Sc. Phys et Nat ' vol 11. p 327 

 1884. 



