196 DR. JAMES BOTTOMLEY ON THE ABSORPTION 



diffusions it was a little difficult to determine this exactly. 

 On the whole I think that the above experiments are 

 favourable to the assumption that for a column of fluid 

 containing finely divided carbon in suspension the relation- 

 ship Q/= constant holds^ if the intensity of the transmitted 

 light remain constant. If we represent the above results 

 graphically, and take as the theoretical curve the rectan- 

 gular hyperbola xy= 25 "44, it will be seen that the results 

 of the experiments do not depart far from the curve. 



In a paper read at the last Meeting of the Section I 

 suggested a method for testing the assumed laws of the 

 absorption of light. I have also applied the same reasoning 

 and method of experiment to carbon diffusions. In one 

 series of experiments I took a diffusion containing i'934 

 cub. c. in 500 cub. c. The standard shades of grey used 

 were : — one consisting of i o grms. BaSO^. and 0"0 1 2 of lamp- 

 black (this I denote byWa) ; tbe other consisted of 10 grms. 

 of BaSO^. and 0*048 of lamp-black (this I denote by Wb) . 

 The materials were well incorporated by shaking and 

 grinding. To the powder I then added a little water, so as 

 to obtain a mixture of suitable consistence to be used as 

 a paint. This was applied by a brush to pieces of cardboard, 

 so as to obtain uniform surfaces. These surfaces were then 

 dried. The colorimeters employed were the same as in the 

 last experiments. I looked at Wb through a column 3 cm. 

 long. I held the other cylinder over Wa, and endeavoured 

 to get the same tint. The mean of two columns, one 

 probably a little too long and the other probably a little too 

 short, gave 8*2 as the proper length ; so I made the column 

 of this length; I thought that the tints were the same. Now, 

 if the law hold with regard to turbid solutions, if we increase 

 both columns by the same length the tints will again 

 correspond. I took 4 cm. as the common increment; the 

 lengths of the columns were made 7 and 12-2; I thought the 



