SOME COLORIMETHICAL EXPERIMENTS. 261 



lined with tin, and condensing in a tin condenser. Now, 

 such water would not be wholly free from oxidizable 

 matter ; hence, in a little while, there will be a depreci- 

 ation in the tint of the permanganate solution. If the 

 tint be strong, the error arising from this cause may be 

 neglected ; but when the tint is feeble, the error is appre- 

 ciable. If the depreciation in tint in the two solutions 

 compared were proportional to the depth of tint in each, 

 this source of error might be neglected ; but, inasmuch as 

 the same quantity of water has been used in making each 

 solution, an equal amount of depreciation is introduced 

 into each. Some of the foregoing experiments will be 

 affected by this source of error. Small sources of eiTor 

 which may be neglected when we deal with ponderable 

 quantities, become of sufficient magnitude to vitiate 

 results when we deal with traces. 



For experiments with a yellow solution I took a solution 

 of bichromate of potash. Standard solution lo in 500 

 cub. c. of water (depth 8 "3) : — 



Still stronger solutions of the bichromate were compared 

 with this standard ; but the discrepancies were considerable. 

 Some of the results also given in the last table are not 

 very good; this more especially applies to the third and 

 fourth results. On another occasion I repeated some of 

 these experiments with the following results. Standard 

 solution same as last : — 



