COLORIMETRICAL EXPERIMENTS. 39 



with some additional remarks on colorimetry. In my last 

 paper I took -oooi gram as the unit of measurement. 

 Por comparison I have retained it in this, although the 

 quantities used can no longer be considered as traces. The 

 colouring-matter used was ammonio-sulphate of copper. 

 A solution was made by dissolving lo grams of crystallized 

 sulphate of copper in a mixture of 200 cubic centimetres 

 of water and 50 cub. c. of ammonia. Mixtures of various 

 degrees of intensity were made by taking portions of this 

 solution and mixing with water so as to make up 

 500 cub. c. As in my last paper, A denotes the amount 

 of the colouring-salt present, B the length of the column 

 of fluid, and C the amount of the colouring-salt thence 

 derived by calculation. 



Standard solution 4000 in 500 cub. c. of water, depth of 

 disk 8-3 :— 



ABC 



6000 4'3 77^i> 



a result considerably remote from the correct value. Also 

 when the disk was placed inside the solution at the depth 

 given by theory, it seemed too dark. Next, a comparison 

 was made by looking through the cylinders at external 

 white surfaces ; standard solution 4000 in 500 cub. c, of 

 water, length of column 8*4 : — 



ABC 



6000 5'i 6588. 



Thus the result is considerably different from the real 

 value. Also both experiments concur in giving too high a 

 value. The theoretical depths, moreover, were tried with 

 external sui-faces, and seemed slightly too great. My next 

 experiments were made with solutions containing 2400 and 

 1600 of sulphate of copper. The disk being inside, the 



