Chemical Constitution of Saline Solutions. 305 



CuBi^'SHoO is a finely crystallized salt with a greenish golden colour. With 

 one-third of its weight of water it forms an intensely dark madder brown solution. 

 The added water here corresponds to about four molecules if the anhydrous 

 salt were used, or six molecules with the above crystallized hydrate. If the 

 saturated solution be mixed with Ij to \^ volumes of water, it is changed to a 

 grass-green liquid ; a further addition of 1^ volumes of water yields a blue solu- 

 tion ; and if the addition of water be continued until the liquid is increased to seven 

 times that of the original solution, a blue colour indistinguishable from that of 

 cupric sidphate is the result. 



The lustrous black anhydrous salt, CuBr2, dissolves in water with the same 

 brown colour, and undergoes the same colour changes upon dilution. It is 

 remarkable to see the golden green crystals come out of the solution, which is 

 almost black. There is also a remarkable similarity between the colour of the salt 

 when partially dehydrated and that of the concentrated solution. 



This cupric bromide, CuBrs'SHjO (see p. 302), is a striking example of a 

 peculiarly unstable condition which characterises the copper and nickel haloid 

 compounds. The simple exposure of the crystals to ordinary undried air at or 

 about 16^ causes them to become of a very dark brown colour, almost black, and 

 of the same colour as the solution ; and at the same time that they undergo this 

 change in colour, they lose as much as 9 per cent, of water. In other words, 

 they effloresce and become brown. In this condition, the compound undergoes 

 deliquescence in moist air, forming a very dark brown solution. 



NiBra'OHaO, rich emerald green crystals, behaves in the same manner as the 

 cupric bromide; that is to say, it effloresces and becomes brown. A concentrated 

 solution made by adding water to the amount of about one-third the weight of 

 the salt is reddish brown. The amount of added water is from three to three and 

 a-half molecules to one of salt. When two volumes of this solution are mixed witli 

 one and a-half volumes of water, the colour changes to a rich yellowish green ; if 

 made up to three times its original volume, the liquid is apple-green in colour. 



It is quite evident that at 16° and 20°, the most stable hydrates of the 

 foregoing compounds are CuCls-HsO, CuBra-HaO, and NiBr2-2Il20. 



Nickel Iodide, NiL-OHsO, the bluish green crystals of the compounds behave 

 like the cupric and nickel bromides. A solution made from the crystals, with a 

 minimum of water, is of a yellowish brown colour. 



The addition of 2^ volumes of water converts it into a yellowish green liquid, 

 which does not undergo any fm-ther alteration by dilution. 



Solutions in Alcohol. 



The yellow anhydrous cupric chloride, CuCL, dissolves in alcohol with a 

 brown colour. The dihydrated salt, CuCl2-2H20, dissolves in alcohol with 



XliANS. EOY. DUB. SOC, N.S., VOL. VII., PAKI VII. 



2U 



