ANALYSIS OF URINE 549 



The residue is extracted with boiling water, the particles of iron oxide being 

 broken up with a glass rod as completely as possible. The extracts are filtered 

 into a glass evaporating dish of 3 J inches diameter. The soluble sodium and 

 potassium salts are generally dissolved out when water sufficient to fill the dish 

 has been used, but another 50 c.c. may be employed. 



The aqueous extract is evaporated nearly to dryness after adding 2*5 c.c. 

 of 20 per cent, perchloric acid solution 1 (sp. gr. 1-125); the evaporation is 

 carried so far that there is a vigorous evolution of heavy white fumes of per- 

 chloric acid and is conveniently effected on a sand-bath ; should the evapora- 

 tion proceed to dryness and no spirting occur, the residue may be dissolved 

 in a few drops of perchloric acid solution. 



The evaporated solution is stirred with 20 c.c. of 95 per cent, alcohol; 

 after settling, the liquid is poured through a 9 cm. filter paper, which has been 

 dried to constant weight at 100 in a stoppered weighing bottle (2 x i inches), 

 or on a Gooch with a layer of asbestos \ inch thick ; the residue is treated with 

 10 c.c. of 95 per cent, alcohol containing '2 per cent, of perchloric acid; 2 

 the insoluble potassium perchlorate is transferred to the filter, the last portions 

 being washed upon it by means of 20-30 c.c. of the alcohol containing 

 perchloric acid. The perchloric acid is washed away by a minimal quantity 

 of alcohol as shown by testing the washings with sensitive litmus paper. It is 

 important to wash the top edges of the filter paper thoroughly as it will blacken 

 on the subsequent drying at 100; 120-150 c.c. of alcohol may be used. 



The paper is dried in the funnel at 100 for 20 minutes and then in the 

 weighing bottle until the weight is constant (i mgm. KC1O 4 = 0*3401 mgm. 

 K 2 0). 



As Cobaltinitrite. 



H. H. Green 3 has adapted the cobaltinitrite method for estimating potas- 

 sium in urine : 



25 c.c. of urine are evaporated to dryness in a platinum dish and 

 gently ignited at a dull-red heat. The ash is moistened with nitric acid and 

 reignited until it is free from organic matter and ammonium salts. The ash 

 is dissolved in water containing a few drops of dilute hydrochloric acid and 

 washed into a 200 c.c. porcelain basin. The solution is neutralised or made 

 slightly alkaline with a few drops of caustic soda, acidified with acetic acid 

 and evaporated to between 5 and 10 c.c. i c.c. of glacial acetic acid and 

 10 c.c. of cobaltinitrite reagent 4 are added and the evaporation continued 

 until the syrup will set to a stiff mass on cooling. The cold mass consisting 

 of the yellow precipitate, K 2 NaCo(NO 2 ) 6 . H 2 O, embedded in a dark-pfurple 

 matrix, is stirred up and allowed to soak with 50 c.c. of 10 per cent, acetic 

 acid until the precipitate is disentangled and the solution has a tawny colour. 

 The yellow precipitate is washed by decantation with dilute acetic acid, the 

 washings being poured through an asbestos filter. The precipitate is com- 

 pletely transferred to the filter, washed with cold water and sucked dry. 

 Six washings by decantation with altogether 300 c.c. are generally sufficient. 

 Complete retention of the precipitate may be attained by using a second disc 

 of asbestos on the first. 



1 This suffices for -2 gm. of a mixture of KC1 + NaCl, but 5 c.c. more of perchloric 

 acid must be added if the quantity be greater. 



2 Prepared by adding 5 c.c. of 20 per cent, perchloric acid to 500 c.c. of alcohol. 

 3 Biochem. J., 6. 



4 This is prepared by dissolving 113 gm. of cobalt acetate in 400 c.c. of water and adding 

 roo c.c. glacial acetic acid ; 220 gm. of sodium nitrite are separately dissolved in 400 c.c. of 

 water and the two solutions are mixed with stirring. The last portions of NO 2 are removed 

 by evacuation or by blowing air through the solution. After 24 hours any sediment is 

 filtered off and the volume diluted to i litre. The solution has a dark-plum colour, is kept 

 in the dark and is decanted before use. 



