APPENDIX TO CHAPTER V 159 



Usable compounds with zinc chloride and cadmium chloride are known 

 and are dissociated by water. 



Creatine reduces Fehling's solution without separation of cuprous 

 oxide and is oxidised by boiling with mercuric oxide to methyl 

 guanidine oxalate (Dessaignes [1854, 1855]) and also by Fenton's re- 

 agent (hydrogen peroxide and ferrous sulphate, Dakin [1906]); in the 

 latter case glyoxylic acid is the chief other product. When it is 

 heated with dilute mineral acids, with water, or by itself, creatinine 

 is formed. On boiling with barium hydroxide it forms urea and 

 sarcosine (Liebig [1847]) and also methyl hydantoin (Neubauer 

 [1866, l]). Heating with soda lime causes it to give off methyl- 

 amine. 



Physical and chemical properties of creatinine. Creatinine generally 

 forms anhydrous monoclinic prisms ; on slow evaporation of a cold 

 saturated solution it also crystallises with 2H 2 O in large tables and 

 prisms, which easily effloresce (Worner [1899]). It is considerably 

 more soluble in water than creatine, the solubility being i : 10*6 at 14 

 and i : 1078 at !7(Toppelius and Pommerehne [1896] ; according to 

 Liebig one part dissolves in 1 1 '5 parts of water at 1 5). Creatinine 

 is also more soluble than creatine in cold absolute alcohol, namely 

 I : 625 (Toppelius and Pommerehne [1896]). In hot alcohol much 

 more dissolves, but hardly any in ether. 



Creatinine solutions have an acrid taste and are hardly alkaline to 

 litmus. The substance is, however, a stronger base than creatine 

 (dissociation constant 3-57 x io~ u at 40-2; Wood [1903]) and is 

 precipitated by phosphomolybdic acid, phosphotungstic acid (limits 

 I : 1 2,000 on prolonged standing, according to Hofmeister [1880], and 

 I : 25,000 according to Demjanowski [1912, under methylguanidine]), 

 mercuric nitrate, mercuric chloride (i : 3000) and by silver nitrate after 

 careful addition of ammonia (hence it occurs in the histidine fraction of 

 bases ; Kutscher [1905]). It is not precipitated by potassium tri-iodide. 

 The reducing properties of creatinine are similar to those of creatine. 

 On boiling with Fehling's solution the cuprous oxide formed at first 

 remains dissolved as a compound with unattacked creatinine (Maschke 

 [1878], Korndorfer [1904, 2]), but after prolonged boiling with 

 excess of the reagent cuprous oxide separates creatinine is the chief 

 cause of the slight action of normal urine on Fehling's solution. Un- 

 like glucose, creatinine does not reduce alkaline bismuth solutions. 

 Mercuric oxide, potassium permanganate, lead peroxide and sulphuric 

 acid oxidise creatinine to methylguanidine and oxalic acid ; Fenton's 

 reagent produces methylguanidine, formaldehyde, formic, carbonic, 



