400 PHYSIOLOGICAL CHEMISTRY 



. Creatinine crystallizes in colorless, glistening monoclinic prisms (Fig. 

 128, page 399) which are soluble in about 12 parts of cold water; they 

 are more soluble in warm water and in warm alcohol. It forms salts only 

 with strong mineral acids. One of the most important and interesting 

 of the compounds of creatinine is creatinine-zinc chloride, (C4H 7 N 3 O)2- 

 ZnCt, which is formed, from an alcoholic solution of creatinine upon 

 treatment with zinc chloride in acid solution. Creatinine has the power 

 of reducing cupric hydroxide in alkaline solution and in this way may 

 interfere with the determination of sugar in the urine. In the reduction 

 by creatinine the blue liquid is first changed to a yellow, and the forma- 

 tion of a brownish-red precipitate of cuprous oxide is brought about only 

 after continuous boiling with an excess of the copper salt. Creatinine 

 does not reduce alkaline bismuth solutions and therefore does not inter- 

 fere with Nylander's and Boettger's tests. 



It has recently been shown by Folin that the absolute quantity of 

 creatinine eliminated in the urine on a meat-free diet is a constant 

 quantity different for different individuals, but wholly independent of 

 quantitative changes in the total amount of nitrogen eliminated. 

 Shaffer has very recently confirmed these findings and has shown that 

 the output of creatinine under these conditions is constant from hour 

 to hour as well as from day to day. 



EXPERIMENTS ON CREATININE 



i. Preparation of Pure Creatinine from Urine (Folin-Benedict 1 ). To 10 

 liters 2 of undecomposed urine in a large precipitating jar add with stirring a hot 

 solution of 1 80 grams of picric acid in 450 c.c. of boiling alcohol. Allow to stand 

 over night and syphon off the supernatant fluid. Pour the residue upon a large 

 Buchner funnel, drain with suction, wash once or twice with cold saturated picric 

 acid and suck dry. Treat the dry or nearly dry picrate in a large mortar or evap- 

 . orating dish with enough concentrated HC1 to form a moderately thin paste (about 

 60 c.c. of acid for each 100 grams of picrate) and stir the mixture thoroughly with 

 the pestle for 3-5 minutes. Filter with suction on a hardened paper, and wash 

 the residue twice with enough water to cover it, sucking as nearly dry as possible 

 each time. Transfer the filtrate to a large flask and neutralize with an excess of 

 solid magnesium oxide (the "heavy" variety is best). Add this oxide in small 

 portions with cooling of the flask under running water between the additions. 

 Neutralization of the acid will be indicated by a bright yellow color of the mix- 

 ture, or litmus paper may be used to test it. Filter with suction. Wash the 

 residue twice with water. Immediately add a few cubic centimeters of glacial 

 acetic acid 4o the filtrate to make it strongly acid. Pay no attention to any 

 precipitate that may form, but dilute the solution with about 4 volumes of 95 per 



1 Benedict: Jour. Biol. Chem., 18, 182, 1914. 



Folin: Ibid., 17, 463, 1914. 



8 If it is simply desired to demonstrate the presence of creatinine, i liter may be em- 

 ployed and the various reagents reduced accordingly. 



