58 Mr. Cooper on the Colours that enter into the 



By solving this equation, we obtain y = 2. From which 

 we deduce x = \. 



Thus, it appears, that in the supposed mixture there 

 were 6 grains of potash and 8 grains of soda. 



The numbers in the preceding example were made as 

 simple as possible, that the nature of the process might be 

 understood at a glance. But it may be worth while, for 

 the sake of those analysts who are not familiar with alge- 

 braic computations, to give a general formula, and then 

 explain it by simple arithmetic. 



Let the atoms of potash be . . x 



soda . . . . y 



Let the weight of sulphates be . a 



,, ,, sulphuric acid b 



,, ,, chlorides . . c 



,, ,, chlorine . . d 



y =c 5« + Qd — 5 b — 6 c 



2 

 x = a — b — 4 y 

 6 

 Add together five times the weight of the sulphates and 

 six times the weight of the chlorine. From this sum, 

 subtract five times the weight of the sulphuric acid and six 

 times the weight of the chlorides. Divide the remainder 

 by two ; the quotient represents the number of atoms of 

 potash in the mixture. This number multiplied by six 

 gives the grains of potash present. 



If we subtract the weight of the potash from the weight 

 of the mixture of potash and soda, determined by para- 

 graphs 1 and 2, the remainder will be the weight of the 

 soda present in the mixture. 



Article VII. 



On the Number and Character of the Colours that enter into 

 the Comjiosition of White Light. By Paul Cooper, Esq. 

 ( Continued from vol. ii. p. 365. ) 



Sir Isaac Newton proved, upon mathematical principles, 

 that when a prism is fixed in the position in which the 

 coloured image of the sun becomes stationary, and the re- 



