662 URINE. 



a crystalline precipitate of a nitroso-compound (C4H 6 N402) of creatinine 

 separates on stirring (KRAMM *) . If, on the contrary, the yellow solu- 

 tion is treated with an excess of acetic acid and heated, the solution 

 becomes first green and then blue (SALKOWSKI 2 ) ; finally a precipitate 

 of Prussian blue is obtained. 



A reaction which in description is similar and which, although not solely 

 (ARNOLD) but at least partially (HOLOBUT), appears after partaking of protein 

 food or meat soup is ARNOLD'S reaction. 3 This reaction is not due to creati- 

 nine. If 10-20 cc. urine are treated with a few drops of a 4 per cent sodium 

 nitroprusside solution and then with 5-10 cc. of a 5 per cent sodium or potassium 

 hydroxide solution, at first a strong and pure violet color is obtained with an 

 absorption band between D and E, then it becomes purple-red and then brown- 

 red and finally yellow. On the addition of acetic acid the violet or purple-red 

 color passes into blue, which soon becomes pale and finally a pale yellow color. 

 It differs from the creatinine in color and absorption band as well as in that the 

 creatinine reaction requires more sodium nitroprusside. 



In preparing creatinine from urine the creatinine-zinc chloride is first 

 prepared according to NEUBAUER'S 4 method. Creatinine may also be 

 prepared from urine by precipitating with a mere uric -chloride solution 

 according to either MALY'S or JOHNSON'S 5 process. 



The best method for preparing creatinine is the following, suggested 

 by FoLiN. 6 The creatinine is first precipitated as the double picrate 

 of creatinine and potassium by means of picric acid according to JAFFE'S 

 method, and then this precipitate, while still moist, is decomposed by 

 KHCO 3 and water. The solution, which contains the creatinine besides 

 potassium carbonate and small amounts of impurities, is neutralized 

 with sulphuric acid and the sulphate precipitated by alcohol. The 

 creatinine is now converted into the double zinc-chloride salt and this 

 last treated with moist lead hydroxide. After the removal of the lead, 

 the solution contains a mixture of creatinine and creatine, which last is 

 completely transformed into creatinine by heating for forty-eight hours with 

 normal sulphuric acid. After exact neutralization with barium-hydroxide 

 solution it is concentrated to the point of crystallization. 



The quantitative estimation of creatinine used to be performed accord- 

 ing to NEUBAUER'S method for the preparation of creatinine, or more 

 simply by SALKOwsKi's 7 modification of this method. As this method 

 is now seldom used we refer the reader to other hand-books. 



FOLIN 8 has suggested a colorimetric method for determining creatinine 

 which is based upon JAFFE'S picric-acid reaction and is as follows: 10 

 cc. of the urine are treated in a graduated flask of 500 cc. capacity 

 with 15 cc. of a 1.2 per cent solution of picric acid and 5 cc, of a 10 

 per cent NaOH solution. After shaking and allowing to stand\or five 



1 Centralbl. f. d. med. Wissensch., 1897. 



2 Zeitschr. f. physiol. Chem., 4. 



3 Arnold, Zeitschr. f. physiol. Chem., 49; Holobut, ibid., 56. 



4 Ann. d. Chem. u. Pharm., 119. 



5 Maly, Annal. d. Chem. u. Pharm., 159; Johnson, Proceed. Roy. Soc., 43. 



6 Zeitschr. f. physiol. Chem., 41. 

 ''Ibid., 10 and 14. 



8 Ibid., 41. 



