556 Drushel — Estimation of Potassium in Animal Fluids. 



the boiling point and adding an excess of potassium free barium 

 permanganate. Heintz treated 20 cm3 to 30 cm3 of clear urine 

 with chlorplatinic acid and a threefold volume of a 1 : 4 ether 

 and absolute alcohol mixture. After standing 24 hours the 

 precipitate was filtered off, washed with alcohol," dried, ignited 

 and weighed. The residue was then extracted with hot water 

 and again dried and weighed. The amount of potassium 

 chloride was found bj taking the difference of the weights. 

 It has been repeatedly shown that appreciable amounts of the 

 alkali salts are carried down by barium sulphate, which can 

 not be completely removed by washing. This objection applies 

 to all of the methods in which the sulphate radical is removed 

 by means, of a barium salt. The loss of alkalis is especially 

 appreciable where a large amount of barium sulphate is formed 

 in the presence of relatively small amounts of the alkali salts. 



In 1898 K. Gilbert devised a method for . the separation of 

 potassium which does not require the previous' removal of the 

 sulphate radical. He treated a potassium salt solution free 

 from mineral acids with an excess of sodium cobalti-nitrite acidi- 

 fied with acetic acid. After standing from 12 to 20 hours the 

 potassium was quantitatively separated out as potassium sodi- 

 um cobalti-nitrite which could be freely washed with cold 

 water without an appreciable loss. Gilbert decomposed this 

 precipitate by heating with dilute hydrochloric acid and esti- 

 mated the potassium as the perchlorate or chlorplatinate. 



A few years later Autenrieth and Bernheim* used Gilbert's 

 method for separating potassium in urine, subsequently esti- 

 mating the potassium as the perchlorate. They used 6 cm3 to 

 10 cm3 of concentrated sodium cobalti-nitrite to precipitate the 

 potassium in 50 cm3 of urine. At this dilution it had been 

 shown by Gilbert that the potassium is quantitatively precipi- 

 tated and that the precipitate is apparently of indefinite com- 

 position. In 1900, however, Adie and Wood* found that with 

 a sufficiently high concentration of the reagent and of the 

 potassium salt solution a precipitate of definite composition, 

 represented by the formula K 2 NaCo(N0 2 ) 6 .H 2 0, is obtained. 

 They further found that by decomposing this precipitate with 

 boiling dilute sodium hydroxide and titrating the nitrites with 

 standard potassium permanganate the potassium may be esti- 

 mated with a fair degree of accuracy. 



In a previous paper* from this laboratory it was shown that 

 it is unnecessary, after adding the cobalti-nitrite 'reagent, to 

 let the mixture stand from 12 to 20 hours, if it is evaporated 

 nearly to dryness, also that the precipitate may be directly oxi- 

 dized with potassium permanganate without previously decom- 



* Zeitschr. physiol. Chem., xxxvii, 39. f Jour. Cliem. Soc, lxxvii, 1076. 

 % This Journal, xxiv, 433, 1907. 



