( 365 ) 



tion of milk of lime to separate the phosphates, a part of the erea- 

 tinin is changed into creatiii. This danger may be lessened but 

 not wholly avoided by acidifying the fdtrate before evaporation by 

 means of hydrochloric acid, after which at the end the hydrochloric 

 acid must be eliminated by addition of sodium acetate in order not 

 to hinder the precipitation of creatinin zinc chloride. But there are 

 other difiiculties connected with the method of Neubauer which can 

 never be totally removed. The urine is after the removal of the 

 phosphates concentrated till it obtains the consistency of ajrnp and 

 is than extracted with alcohol. In the mass of salts rendered hard 

 by the contact with alcohol, a part of the creatinin may be retained 

 nndissolved. If in order to eliminate this difficulty the urine is not 

 very much e^'aporated, there arises another source of error. The 

 alcohol is diluted by the still resting Avater and the consequence 

 is that now the creatinin-zincchloride crj^stallises only partially. For 

 this compound is insoluble in absolute alcohol but not in alcohol 

 containing water. A too small quantity of creatinin is therefore 

 always found b}^ the application of this method. 



Van Hoogenhüyzen and Verploegh have investigated the solubility 

 of creatinin-zincchloride in alcohol by putting dried crystals, prepared 

 from urine and purified as much as possible, in closed bottles under 

 alcohol of ditferent strength at the temperature of the room under 

 repeated shaking and by determinating afterwards, by means of 

 Folin's method, how much creatinin was dissolved in the alcohol. 

 They found : 



in 'iOO C.C. alcohol 99 7o trace of creatinin. 

 „ „ „ „ 93 7o 5.6 mgr. „ 



jj >) }} J) '-^ /o oZ.l „ „ 



1, 5> >> j> 5U /o 104. 5 ,, ,, 



In connection with this thej' obtained out of urine more creatinin- 

 zincchloride when the alcoholic extract before the addition of chlorid 

 of zinc was again evaporated to almost dryness and then dissolved 

 by strong alcohol, than with the usual method. They could still show 

 creatinin in the liquid fdtered off from the creatinin-zinc-chlorid as 

 well by the reaction of Weyl as by that of Jaffe. So the method 

 of Neubauer always gives a loss of which the amount cannot be 

 estimated. One is therefore not entitled to attribute much value to 

 the little oscillations in tiie output of creatinin found by applying 

 this method. 



By the method of Folin on the contrary sucli a source of uncer- 

 tainty does not exist, when the time of the reaction — 5 minutes — 

 is rightly observed, the liquid is brought to the exact volume with 



