258 DR. CHARLES A. BURGHARDT ON COPPER-ORES. 



crystalline state. A curious fact I may mention, viz. that 

 natural cupric oxychloride should increase in hydration by 

 three atoms of water. 



XXXIII. On some Colorimetrical Experiments. 

 By James Bottomley, B.A., D.Sc. 



Read before the Physical and Mathematical Section, 

 April 23rd, 1878. 



If a white disk be sunk in a coloured solution, the inten- 

 sity of the colour perceived will be a function of the depth 

 of the disk and the quantity of colouring-matter present. 

 If, in any set of experiments, we make the intensity of 

 colour constant, then the depth of the disk will be a 

 function of the quantity of colouring-matter only. Occa- 

 sionally in chemistry we have to deal with quantities so 

 minute that we can no longer use the balance for their 

 determination ; and yet those small quantities, when they 

 yield coloured solutions, are evidently comparable among 

 themselves. In a short communication which I made to 

 this Society (vol. xv. p. 63) I suggested that such a pro- 

 cess as above indicated might be applied for the measuring 

 of such traces, assuming that the depth of the disk would 

 be inversely as the quantity of colouring-matter present. 

 Some experiments were made on colouring-matter in so- 

 lution. Glass cylinders were used about 10 inches high 

 and 2 inches in diameter. To one side of each cvlinder was 



