32 LABORATORY WORK IN PHYSIOLOGICAL CHEMISTRY. 



same way, with an equal amount of water (save residue). 

 Unite the two extracts, and after concentration to about 200 

 c.c. acidify the solution with 2 or 3 drops of acetic acid. 

 Remove the coagulated proteids by filtration, and to the fil- 

 trate * add basic lead acetate, carefully avoiding any excess; 

 the precipitate consists of phosphates, chlorides, sulphates, etc. 

 Allow this to settle and then filter. Warm the filtrate and 

 pass H 2 S through it to remove the excess of lead. Filter hot. 

 The filtrate, which should be water-clear, is then concen- 

 trated on a water-bath to a thin syrup. Upon standing sev- 

 eral days in a cool place crystals of creatine will deposit. Filter 

 off the crystals, and wash them with 88 per cent alcohol. 

 (Keep the filtrate for the separation of the purine bases.) 



Place some of the crystals in a small flask with 10 c.c. 

 dilute H 2 SO 4 , and heat for half an hour on the water-bath, 

 keeping the volume constant. While still warm add BaC0 3 , 

 in substance, to neutralization. Filter and evaporate the 

 filtrate to 10 c.c. The creatine has been changed to creatinine. 

 Write the equation. Perform the following tests with the 

 solution: 



(a) Place 2 drops of the solution upon a watch-glass and 

 add to it a few drops of an alcoholic solution of ZnCl 2 ; allow 

 it to stand for several days and then examine the crystals 

 under the microscope. 



(6) Weyl's Reaction. To 2 c.c. of the creatinine solution 

 add three drops of a freshly prepared dilute solution of 

 sodium nitroprusside. Then add, drop by drop, dilute 

 NaOH. A ruby-red color is produced which quickly changes 

 to yellow. If the solution is now acidified with acetic acid 



* This filtrate corresponds to Liebig's extract, and if the latter is used 

 for study instead of chopped beef, the procedure of separation is taken 

 up at this point. 



