OF LIGHT BY TURBID SOLUTIONS. 189 



seemed probable, from reflection upon the mode of distri- 

 bution o£ the particles throughout the mass of fluid, that 

 the function would be the same as for transparent solutions. 

 In the latter case both experiment and reasoning from 

 first principles concur in giving a formula "l^ak^ for the in- 

 tensity of light passing through a column t units long. As 

 I have pointed out in another paper, this implies an ex- 

 pression of the form XaK^, denoting the connexion between 

 the transmitted light and the quantity of colouring-matter. 

 Therefore we might expect a similar expression to hold in 

 the case of diffusions (the term seems to me more conve- 

 nient than to speak of turbid solutions). If such be the 

 case, one consequence will be that, if we have two cylinders 

 containing in equal bulks of water Q and Q,' of solid 

 matter in suspension, if we adjust the columns so as to 

 obtain the same intensity of light when we regard an 

 external white surface, then the lengths of the columns 

 will fulfil the condition Q,^ = Q'/'. 



The carbon that I used was lamp-black recalcined in a 

 covered platinum crucible. After being so treated it 

 seemed blacker than it did before. Of this 0-417 gram 

 was ground up in a mortar with 10 drops of a solution of 

 gum. The contents of the mortar were then rinsed out 

 with water and difi'used by shaking through 500 cub. c. of 

 water. This was poured into a cylinder ; the length of 

 the column was 22-5 centimetres. After the lapse of 24 

 hours I drew off by a pipette the upper portion; the 

 column so removed was 15-8 centim. long. This carbon 

 difi'usion contained so much solid matter that I found it 

 inconveniently strong for experiments; so, as occasion 

 required, I made weaker diff'usions, containing in 250 cub. 

 c. 5, 10, 20, or 40 of the stronger diff'usion. Of -these 

 weaker liquids portions were taken and mixed with water 

 so as to yield a bulk of 500 cub. c. I stated above that 



