172 P. C. OH the Colours that enter into the [Sept. 



It is tasteless, yet leaves a disagreeable impression in the 

 mouth. Its specific gravity is 1-76176. 100 parts of water 

 at 57°, dissolve 0*056 of the salt. The solution is colourless 

 and tasteless. 100 parts of boiling water dissolve 1*724 

 parts of it. The solution has a fine green colour, and when 

 cooled slowly, deposits the salt in small crystals, which, 

 under the microscope, seem to be flat rectangular prisms, 

 with rectangular bases. 



When this salt is heated, it gradually blackens, then 

 burns with a strong flame, and the greatest part of the 

 nickel is volatilized ; for, 20 grs. of the salt, treated in 

 this way, left only 1^ gr. of peroxide of nickel. 



To form an estimate of the quantity of combined vrater 



which it contained, 20 grs. of it were left for 24 hours in 



the vacuum of an air pump, over sulphuric acid. The 



weight was reduced to 16*62 grs. This residue being heated 



for two hours on the sand-bath, in a temperature of 284°, 



was reduced in weight to 14*25 grs. Now, if this residue 



was anhydrous, it must have contained 4*845 oxide of nickel, 



and 9*405 racemic acid. This would make the constituents 



Racemic acid . . 9*405 or 8*25 



Oxide of nickel . . 4*845 „ 4*25 



Water 2*370 „ 2*08 



16*620 

 If we admit that the salt dried at 284° still retained a very 

 little water, the combined water will amount to two atoms. 

 This, doubtless, represents the true constitution of the salt. 

 Carbonate of nickel may be dissolved in an excess of 

 racemic acid, by the assistance of heat. On cooling, a 

 bluish green powder falls, inferior in beauty, to the race- 

 mate, by double decomposition ; but, its constitution is the 

 same. (To he continued.) 



Article II. 



On the Number and Character of the Colours that enter into 



the Composition of White Light. By P.O. 



( Continued from p. 119.J 



It was my intention, when I concluded the last paper on 

 this subject, to proceed to some experiments of a different 

 character ; but the highly interesting papers on Accidental 



