192 METHODS FOR THE ANALYSIS OF BLOOD 



If this is not sufficient to clear up the H^SCX, two to three drops of 

 HN0.3 are added and boiling is resumed until the acid is colorless, 

 when the tube is cooled. 



The oxidation mixture is washed into a 50 c.c. beaker, made 

 alkaline to phenolsulfonephthalein with 10 per cent NaOH, and 

 evaporated to dryness on the water bath. A few drops of glacial 

 acetic acid are added, until the mixture is acid; then 1 c.c. cobaltic 

 nitrite reagent is added, and evaporation continued until crystals 

 of Na 2 SO4 appear. The mixture is then cooled. Dehydration 

 by means of the Na 2 SO4 results in very complete precipitation of 

 the K 2 NaCo(NO 2 ) 6 . 



The precipitate of potassium sodium cobaltic nitrite is filtered 

 off on a Gooch crucible with a fairly thick asbestos mat. Filter 

 paper must not be used, because during the subsequent boiling 

 with 1 per cent NaOH, considerable reducing substance is formed 

 from it. Just before the mat is sucked dry, a suspension of 

 BaSCU is poured onto it. This not only fills up the larger pores, 

 but serves as an excellent test of the mat. Before the water has 

 all passed through the mat, the contents of the beaker containing 

 the potassium sodium cobaltic nitrite are poured on. The beaker 

 is rinsed with 4 to 5 c.c. of cold water, and the rinsings are poured 

 onto the nearly dry mat. Such washing, with 2 to 3 c.c. of water, 

 is repeated six times. The mat when almost dry is transferred 

 to the beaker, and all adhering particles are washed from the 

 crucible to the beaker with 9 to 10 c.c. of water. One c.c. of 10 

 per cent NaOH is added, and the contents of the beaker are 

 heated to boiling, then cooled. The dark brown mixture is made 

 up to exactly 25 c.c. and centrifuged. Twenty c.c. of the clear 

 fluid are pipetted off into a 150 c.c. Erlenmeyer flask, 5 c.c. of 1 :4 

 H2SO4 added, and titration with 0.02 N KMnO4 as described 

 above is at once carried out. Blanks, run frequently, are usually 

 small (0.05 to 0.10 c.c.). The potassium value of the permanganate 

 is determined by analysis of the standard solution B. This value 

 should be determined frequently, but does not vary greatly from 

 day to day. Calculations are based on the values thus obtained 

 rather than on a theoretical factor. 



