CHEMICAL BASIS OF THE ANIMAL BODY. 147 



from solutions. It crystallises in warty lumps composed of aggregated 

 masses of prisms, or fine needles. 



This compound is formed when a concentrated neutral solution of 

 the zinc salt is added to a not too dilute solution of kreatinin, and since 

 it is almost insoluble in alcohol it is frequently convenient to employ 

 alcoholic rather than aqueous solutions of the two substances. 



Preparation^. This does not admit of any useful brief description, 

 but the principles involved are the following. 



(i) By the action of dilute boiling mineral acids on kreatin. 



(ii) By concentrating large volumes of urine to a small bulk. 

 From this the kreatinin is obtained as a compound either by the 

 addition of chloride of zinc or by precipitation with mercuric chloride. 

 From these compounds it is then separated by boiling with hydrated 

 oxide of lead, and is finally purified by crystallisation. 



It may also be precipitated by phospho-tungstic and phospho-molybdic 

 acids 2 . 



Apart from the characteristic formation of the compound with zinc 

 chloride, kreatinin yields several well-marked reactions of which the 

 following are the more striking. 



1. WeyVs reaction 3 . To the suspected solution a few drops of 

 very dilute sodium nitro-prusside [N& 2 (NO) Fe Cy 5 ] are added, and 

 then, drop by drop, some dilute caustic soda. If kreatinin is present 

 a fine but transient ruby-red colour is obtained which speedily passes 

 into yellow. If the solution is now acidulated with acetic acid and 

 warmed it turns at first greenish and finally blue 4 . This last colour 

 is due to the formation of Prussian-blue 5 . WeyPs reaction is extremely 

 delicate and suffices to detect -0287 p.c. of kreatinin in pure solution or 

 066 p.c. in urine. According to Krukenberg the reaction is best ob- 

 tained by adding the caustic soda first and then a few drops of concen- 

 trated solution of the nitro-prusside. Guareschi recommends the use 

 of 10 p.c. solutions of the respective reagents 6 . 



When applied to urine the absence of acetone should be ascertained 

 since it also gives a similar ruby- red colour, but no subsequent blue can 

 be obtained from it, and the solution when yellow turns red again on 



1 For details see Hoppe-Seyler, Phys.-path. chem. Anal. 1883, S. 182, and 

 Neubauer u. Vogel, Harn-analyse, 1890, S. 228. 



2 For recent synthesis see Horbaczewski, loc. cit. (sub kreatin). 



3 Ber. d. d. chem. Gesell. 1878, S. 2175. 



4 Salkowski, Zt. f. physiol. Chem. Bde. iv. (1880), S. 133; ix. (1885), S. 127. 



5 Krukenberg, Verhand. d. phys.-med. Ges. Wiirzburg, Bd. xvm. (1884), S. 5. 

 Confirmed by Salkowski. Cf. Colasanti, Moleschott's Unters. Bd. xm. (1888), 

 Hf. 6. 



6 Ann. di chim. e difarm. Ser. 4 T. v. (1887), p. 195. 



z. o 



