176 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



in excess to precipitate the phosphates. Filter, and evaporate the filtrate to 

 a small bulk ; to this add 50 c.c. absolute alcohol, and let the mixture stand 

 for six hours. Then add 10 or 15 drops of an alcoholic solution of zinc 

 chloride; the crystals form, and after two or three days' standing in a 

 dark place may be collected on a weighed filter. 



Wash with 90 per cent, alcohol, dry and weigh, and thence calculate the 

 percentage of creatinine. 



4. Estimation of Creatinine. Johnson's Method. — Take 100 c.c. of urine ; 

 add to it 5 c.c. of a saturated solution of sodium acetate, and then 20 c.c. of a 

 saturated solution of mercuric chloride. This produces an abundant precipi- 

 tate of urates, sulphates, and phosphates. Filter. Set the filtrate aside for 

 twenty-four hours, and the mercury compound of creatinine crystallises out. 

 Examine this deposit with the microscope : note it is composed of spherules. 

 For quantitative purposes, this is collected, washed, dried, and weighed in 

 the usual way. One-fifth of the weight obtained is creatinine. Throughout 

 the processes no heat is used, otherwise the characteristic properties of urinary 

 creatinine are altered; but if only a quantitative analysis is wanted the 

 method may be hastened by boiling the first filtrate for ten minutes, instead 

 of letting it stand twenty-four hours. 



In order to separate the base itself (see p. 125), much larger volumes of 

 urine must be employed, for there is considerable loss in the later stages 

 of the process. Johnson himself used some hundreds of litres. 



