11 
PHYSICAL AND MATHEMATICAL SECTION, 
October 14th, 1879. 
E. W. Binney, F.R.S., F.G.S,, President of the Section, 
in the Chair. 
“ On Colorimetry, part III.,” by J ames Bottomley, D.Sc. 
In this paper I give the results of some furthur experi- 
ments to test the accuracy oi 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 difference in sensbility to colour 
of the two eyes, in making the determinations I used one 
eye only. The cylinders used in these and previous experi- 
ments were not specially made for colorimetric purposes. 
