MICROCHEMICAL METHODS FOR BLOOD ANALYSIS 297 



in time the resulting reagent is clear enough for immediate dilu- 

 tion with 10% alkali and water, and the finished solution can 

 at once be used for Nesslerizations. 



1 i The cost of the chemicals called for in this rather interesting 

 process of making Nessler's solution is less than when starting 

 with mercuric iodid and the disagreeable impurities present in 

 many samples of mercuric iodid are avoided. From the stock 

 solution of mercuric potassium iodid, made as described above, 

 prepare the final Nessler solution as follows: 



"From completely saturated caustic soda solution containing 

 about 55 g. of NaOH per 100 c.c. decant the clear supernatant 

 liquid and dilute to a concentration of 10%. (It is worth while 

 to determine by titration that a 10% solution has been obtained 

 with an error of not over 5%.) Introduce into a large bottle 

 3,500 c.c. of 10% sodic hydrate solution, add 750 c.c. of the 

 double iodid solution, and 750 c.c. of distilled water, giving 

 5 liters of Nessler's solution. 



' ' In the absence of modifying circumstances, such as the pres- 

 ence of much acid or alkali, this reagent should be added in the 

 proportion of 10 c.c. per 100 c.c. of the volume to which the 

 Nesslerized solution is to be diluted. As a general rule the 

 volumetric flask (or volumetric test tube) should be at least 

 two-thirds full before adding the Nessler reagent. If attention 

 is not given to this detail turbid mixtures are obtained, and 

 turbid solutions must never be used for color comparisons." 



Preparation of Protein-Free Blood Filtrates. (Folin and 

 Wu: Jour. Biol. Chem., xxxviii, 81, 1919). The blood filtrate, 

 the preparation of which is described below, is suitable for the 

 determination of nonprotein nitrogen, urea, uric acid, creatinin, 

 creatin and sugar. 



The blood should be collected over finely powdered potassium 

 oxalate, about 20 mg. for 10 c.c. of blood. It is important not 

 to use unnecessarily large amounts of oxalate because the excess 

 makes the complete coagulation of the proteins more difficult 

 and also interferes more or less with the uric acid precipitation. 



