184 DR. JAMES BOTTOMLEY ON COLORIMETRY. 



Suppose we alter the lengths of the columns, and in a 

 second experiment we find 



by cross multiplication and elimination of the common 

 factor W,Wi we obtain 



or, as we may write it, 



Then taking the logarithms of both sides and dividing by 

 log k we get finally 



In this way I proposed to test the law. 



I took as standard tints a smooth surface of BaSO^. and 

 another of BaSO^, and carbon in the proportion of lo grms. 

 of BaSO^ to 0'Oo6 grm. of carbon ; these materials were 

 intimately mixed, and the powder reduced by pressure to 

 a flat surface. The colorimeters used were glass cylinders 

 covered externally with black cloth, the circular apertures 

 at the bottom admitting light being 8 mm. in diameter. 



One experiment gave the following results. Length of 

 column 22*2 c, standard tint W, (BaSO^.). I now attempted 

 to get the same intensity when looking through the second 

 cylinder at tint W^ (BaS04 + carbon). '^^^ mean of two 

 trials gave 14' 8 c. as the equivalent column. Hence we 

 have the following results : — 



