W. A. Drushel — Potassium as the Cobalti-nitrite. 435 



From the results of Table I it appears that the oxidizing 

 value of the cobaltic hydroxide in terms of permanganate is 

 nearly one-twelfth of that required for the oxidation of the 

 nitrites, while the amount of permanganate necessary in the 

 presence of the cobalt is nearly eleven-twelfths of that required 

 for the oxidation of the nitrites after the removal of the 

 cobalt. The factor used, therefore, in calculating the results 

 from the direct titration should be twelve-elevenths of that 

 given by Adie and Wood ; that is, in titrating the precipitate 

 without first separating the cobalt one cubic centimeter of 

 strictly \ potassium permanganate is equivalent to O000856 



grm. K„0. 



Unless the potassium salt solution is of the proper concen- 

 tration the precipitate is very difficult to filter and wash, and 

 shows a tendency to pass through the felt. By repeated experi- 

 ments it was found that this difficulty as well as the necessity 

 for allowing the precipitate to stand over night is avoided by 

 evaporating the mixture nearly to dryness on the steam bath 

 after adding the sodium cobalti-nitrite solution in considerable 

 excess. Upon cooling the pasty residue it becomes hard and 

 dry. It is then treated with cold water to dissolve the excess 

 of sodium cobalti-nitrite, and the insoluble portion is collected 

 on the filter. This precipitate may be freely washed with cold 

 water without showing a tendency to pass through the filter, 

 and is so insoluble that less than 0*5 of a milligram of the 

 dried precipitate will dissolve in a liter of water at the room 

 temperature during 24 hours standing with occasional shaking. 

 This mode of treatment was found to work well and was used 

 in all the subsequent experiments. 



The method as worked out and used in all tire experiments 

 except those of Table I is as follows : The solution of a 

 potassium salt, containing not more than 0*2 grm. K 2 and 

 free from ammonium salt, was treated with a rather large 

 excess of sodium cobalti-nitrite solution acidified with acetic 

 acid, and evaporated to a pasty condition over the steam bath. 

 It was then cooled and treated with 50 om3 to 100 cm3 of cold 

 water and stirred until the excess of sodium cobalti-nitrite was 

 dissolved. It was allowed to settle and decanted through a 

 perforated crucible fitted with an asbestos felt. The precipi- 

 tate was washed two or three times by decantation, after which 

 it was transferred to the crucible and thoroughly washed w r ith 

 cold water. In the meantime a measured excess of standard 

 potassium permanganate was diluted to ten times its volume 

 and heated nearly to boiling. Into this the precipitate and 

 felt were transferred and stirred up, after which the crucible 

 was also put into the solution, since particles of the precipitate 

 stick persistently to the sides of the crucible. After the oxi- 

 dation had proceeded five or six minutes manganese hydroxide 



