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 leisures 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 aeids, aqueous solutions of which read 
acid to litmus. With certain salts of the heavy metals it forms crystal- 
line molecular compounds, tw^ of which are of practical importance. 
Creatinin zinc-chloride— (C 4 H 7 N,0) 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.HCl.HgO),3HgCl 2 . This is precipitated in colourless, glassy, 
spherular masses, when sodium acetate and mercuric chloride are added t© 
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 {WeyVs 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 uive Weyl's test direct. 
Jaffa's 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 tins process all the operations are carried out in the cold : by this means the true 
urinary creatinin is obtained. Heat produces isomeric change. 
- Cf., hoAvever, Allen, "Chemistry of Urine," pp. 156 and 159. 
