66 DR. JAMES BOTTOMLEY ON COLORIMETRY. 



VIII. On Colorimetry. — Part III. 

 By James Bottomley, B.A.^ D.Sc, F.C.S. 



Kead before the Physical and Mathematical Section, 

 October 14th, 1879. 



In this paper I give the results of some further experi- 

 ments to test the accuracy of the assumption that, when 

 light is transmitted through transparent coloured solutions, 

 the length of the column multiplied by the quantity of 

 colouring -matter is constant if the colour is constant. In 

 a communication which I made to the Society in April of 

 this year, I gave the results of some experiments with 

 ammonio-sulphate of copper, which appeared to indicate a 

 failure of the law ; but the failure was traceable to the 

 decomposition of the salt by water, and better results were 

 obtained when a suitable menstruum was employed. I 

 was wishful to obtain some colouring-matter which might 

 be diluted with water without decomposition ; it occurred 

 to me that caramel would be a suitable body. I prepared 

 some caramel by heating loaf sugar. The resulting dark 

 brown vitreous mass dissolved entirely in water. In these 

 experiments I also wished to see if the law would hold 

 when one quantity was a considerable multiple of the 

 other ; also the quantities used are no longer mere traces. 

 In order to avoid an ambiguous result from any diflference 

 in sensibility to colour of the two eyes, in making the de- 

 terminations I used one eye only. The cylinders used in 

 these and previous experiments were not specially made for 

 colorimetric purposes. At the bottom they were curved a 



