CREATININ. 599 



neutral to litmus. The crystalline form of the base varies with the 

 method of preparation (Johnson). As ordinarily obtained, it exists as 

 colourless monoclinic prisms, which are often imperfectly formed, and 

 appear of whetstone shape (Fig. 53). It dissolves in about twelve parts 

 of cold water, but requires a hundred parts of alcohol to dissolve it at 

 ordinary temperatures. In ether it is almost insoluble. Creatinin 

 reduces alkaline copper solutions (cf. p. 608). It forms characteristic 

 crystalline salts with the mineral acids, aqueous solutions of which react 

 acid to litmus. With certain salts of the heavy metals it forms crystal- 

 line molecular compounds, two of which are of practical importance. 



Creatinin zinc-chloride (C 4 H 7 N 3 O) 2 ZnCl 2 separates as a precipi- 

 tate, consisting of stellate clusters of acicular crystals, when a concen- 

 trated neutral solution of chloride of zinc is added to an aqueous or 

 alcoholic solution of the base. The compound is soluble in hot water, 

 in mineral acids, and in alkalies; but insoluble in alcohol, and very 

 slightly soluble in cold water. 



Creatinin mercuric-chloride, a complex compound of the formula 

 4(C 4 H 7 N 3 O.HCLHgO),3HgCl 2 . This is precipitated in colourless, glassy, 

 spherular masses, when sodium acetate and mercuric chloride are added to 

 creatinin solutions. The base is also precipitated, even from very dilute 

 solutions, by the addition of phosphotungstic, phosphomolybdic, or picric 

 acids. 



Isolation and estimation. Neubauer separated creatinin from the urine by 

 means of its combination with zinc chloride, this salt being added to an 

 alcoholic extract of the evaporated urine. A more convenient method is to 

 treat the urine direct with a little sodium acetate, and then with one-fourth 

 its volume of saturated mercuric-chloride solution. The precipitate which 

 first falls is at once filtered off; it contains uric acid and other constituents, 

 but not creatinin. The filtrate from this rapidly begins to deposit the mer- 

 cury compound described above, and in forty-eight hours precipitation is com- 

 plete (G. S. Johnson). The base itself is prepared by decomposing this 

 precipitate with sulphuretted hydrogen, and by treating the creatinin-hydro- 

 chloride, so obtained, with hydrate of lead. 1 To determine the quantity, the 

 mercury precipitate may itself be weighed, and the percentage of creatinin 

 calculated from this. 2 



Tests. If a solution of creatinin be treated with a small quantity of 

 very dilute sodium nitroprusside solution, and subsequently with weak 

 caustic alkali, a rich, ruby-red colour is produced, which afterwards 

 changes to yellow ( Weyl's reaction). If acetic acid be now added in 

 excess, and heat applied, the solution becomes green, and then blue, 

 and finally a precipitate of Prussian blue is formed. Acetone (p. 616) 

 gives an analogous reaction, but behaves differently after the addition of 

 the acetic acid. Many specimens of urine will give Weyl's test direct. 



Jaffes test is an application of the fact that creatinin gives, with 

 picric acid and caustic alkali, an intense red colour, even in the cold. 



The variations in the urinary creatinin generally follow very closely 

 those of the urea, but there can be no doubt that its quantity depends 

 largely on the amount of creatin taken with the food. Its physiological 

 relations are discussed elsewhere. Pathologically, it is increased in most 

 febrile conditions, and in diabetes. It has been stated to diminish in 



1 In this process all the operations are carried out in the cold ; by this means the true 

 urinary creatinin is obtained. Heat produces isomeric change. 



2 Cf., however, Allen, "Chemistry of Urine," pp. 156 and 159. 



