108 P. C. on the Colours that enter into tfie [Aug. 



It is a white powder, having an acidulous taste and red- 

 dening vegetable blues. Its specific gravity is 2*555. At 

 the temperature of 55° 100 water dissolve 0*57, and at 108° 

 1*12 of this salt. When a boiling hot solution is evaporated 

 slowly the salt is deposited in transparent crystals, but so 

 irregular that it is next to imp6ssible to determine the 

 form. Under a powerful microscope some of them appear 

 six-sided prisms with unequal faces, but the greater number 

 of them were flat pyramids, seemingly four-sided, with two 

 very large and two very small faces. Many of them were 

 grouped in stars composed of very small four-sided prisms. 



21*4 grains of crystals of racemic acid mixed with 13 

 grains of bi-carbonate of potash were totally converted into 

 bi-racemate. The salt formed weighed 21*9 grains. Now, 

 had the salt contained (as I intended it to do) exactly 16*5 

 grains of real racemic acid and 6 of potash, the weight 

 should have been 22*5. There was a loss of 0*6 grains. 

 This might have been owing to the paper which covered 

 the capsule having imbibed a little of the liquid, for it 

 was spotted the next morning. 22*5 grains of bi-racemate 

 were exposed for an hour to a heat of 320°. The loss of 

 weight was 0*0675. From this I conceive that bi-race- 

 mate of potash is anhydrous. 



Bi-tartrate of potash is so well known that no description 

 of it is necessary. The resemblance of the two salts is strik- 

 ing. Yet there are several particulars in which they differ. 

 (To he continued.) 



Article III. 



On the Number and Character of the Colours that enter into 



the Composition of White Light. By P. C. 



( Continued from Page 34.^ 



The simple and satisfactory explanation of the various 

 appearances of the spectrum in the different stages of its 

 developement, and the impossibility of accounting for these 

 appearances with any other arrangement hitherto proposed, 

 convinced me that the many tints exhibited by nature, must 

 be derived from the three primary colours of violet, green, 

 and red, even before this division of the spectrum had been 

 submitted to the test of experiment. 



