125 



color of the solution darkened At this point from 5 to 25 cc of sulphuric acid (1- 2) 

 u-n- added, and t he rotation, after stirring, was allowed to stand afew minutes Tnpr 

 a measured amount of standard oxalic acid, containing 50 cc of strong sulphuric acid 

 per liter, was run in from a burette taking care to add an excess. The temperature 

 was maintained a little below the boiling point until the solution became colorless 

 and t he manganese hydroxid had completely dissolved. It was then titrated to color 

 by permanganate in the usual manner. From the whole amount of permanganate 

 employed, the permanganate equivalent of the oxalic acid used was subtracted and 

 t!,,- remaind^ multiplied by the factor calculated for the strength of permanganate 

 used, 0.0008o6 being the factor for strictly tenth-normal potassium permanganate 



While work was in progress in the referee's laboratory with a view to testing the 

 adaptability of the cobalti-nitrite methods, letters were received from several coop- 

 erating chemists commending this process quite strongly, as a result of some prelimi- 

 nary work which had been done with it. Mr. A. M. Peter, of the Kentucky station, 

 reported that by the cobalti-nitrite method results of 49.89 and 49.92 per cent were 

 obtain.'.! by Mr. Q. Edgar for sample No. 1, as against 49.82 by the official method, 

 while for sample No. 2, 4.50 and 4.48 per cent of potash was found, as against 4.41 

 by t h<- oili.-ial method. Mr. Baker obtained the following results on the official sam- 

 pl,- by hrur.li.-rs modification: No. 1, 50.24 and 50.85 per cent; No. 2, 4.46 and 4.31 

 nt. Following an- results reported by Mr. Baker, using the original Adie and 

 Wood method, in which precipitation is effected without evaporation: 



1'tnnjnirixnn of pottuk </> ' > munition* hi/ ttu nriijiiinl Adir aiid Wood cobalti-nitrite method 



mt-irir.) and the official method. 



o The kainits and mixed tertillxers evidently did not entirely precipitate owing, probably, to improper 



roruvntr itm::. 



CONCLUSIONS. 



It apiKmre from the result of this year's work, that while some good results are 

 obtained by the volumetric method, there are difficulties connected with the working 

 of the procettt which affect the reliability and rapidity of its execution. Among these 

 may be mentioned the trouble experienced in washing the precipitate free of acid and 

 the tcmlency of the precipitate to run through, while the smallness of the aliquot 

 used in the determinations would, of course, tend to affect the accuracy of the results. 



On this account it would seem desirable that work with this method be held in 

 abeyance for the present and that a trial be made of the cobalti-nitrite method with a 

 \iew to determining its adaptability to fertilizer work. 



The results of tests of the employment of ammonia and ammonium oxalate in potash 

 determinations in j>otash salts indicated that lower figures are secured in this way, so 

 that from this partial investigation the contention of those who claim that the usual 

 method gives impure precipitates would seem to be sustained. However, no positive 

 conclusion can be reached from the limited data at hand and hence this question 

 should be investigated further. 



