SOME COLORIMETRICAL EXPERIMENTS. 259 



pasted a strip of paper marked with an arbitrary scale 

 (each degree of the scale I afterwards found to be 27 mil- 

 lims.); the white surfaces used were crucible-lids ; a piece 

 of glass rod resting on one of the cylinders, having the 

 string of the movable disk attached to it, served as a 

 windlass for raising or depressing it. To avoid the use of 

 many ciphers, I have taken "0001 grm. as the unit of 

 measurement. In the following experiments column A 

 denotes the amount of the colouring-salt present, B the 

 depth of the disk, and C the amount of the colouring-salt 

 thence derived by calculation. Standard solution 35*2 of 

 permanganate of potash in 500 cub. centims. of water 

 (depth of disk 8*3) : — 



ABO 



53 6-1 48 



70 4-1 71 



Experiments were made with still stronger solutions ; 

 but the differences were considerable. Standard solution 

 24 of permanganate of potash in 500 cub. c. of water (depth 

 of disk 8-3) :— 



Still stronger solutions were used with this standard ; 

 but the discrepancies between the true and the calculated 

 quantities were considerable. Standard solution 5*8 in 

 500 cub. c. of water (length of column 8-3) : — 



ABO 



7-2 57 8-4 



Some experiments were made with solutions of perman- 



