THE URINE. 349 



is obtained which quickly turns yellow again (WEYI/S reaction). 

 If we use ammonia instead of caustic soda in this reaction, the red 

 color is not obtained (differing from aceton and ethyl-diacetic acid, 

 LE NOBEL). If the above solution, which has become yellow, is 

 treated with an excess of acetic acid and heated, the solution be- 

 comes first green and then blue (SALKOWSKI) ; finally a precipitate 

 of Prussian blue is obtained. If a solution of creatinin in water (or 

 urine) is treated with a watery solution of picric acid and a few 

 drops of a dilute soda solution, a red coloration lasting several hours 

 occurs immediately at the ordinary temperature, and which turns 

 yellow on the addition of acid (JAFFE'S reaction). Acetone gives 

 a more reddish-yellow color. Grape-sugar gives with this reagent a 

 red coloration only after heating. 



In preparing creatinin from urine the creatinin zinc chloride is 

 first prepared according to NEUBAUER'S method, and this method 

 is also employed for the quantitative estimation of creatinin. In 

 making a quantitative estimation 200-300 c. c. of urine freed from 

 albumin (by boiling with acid) and from sugar (by fermentation 

 with yeast) are measured, alkalized with milk of lime, and treated 

 with CaCl 2 solution until all the phosphoric acid is precipitated ; it 

 is filtered and washed with water, the filtrate and the wash-water 

 united, and evaporated to a syrup after acidifying with acetic acid. 

 This syrup is mixed while hot with 50 c. c. of 95$-97$ alcohol. 

 This mixture is transferred to a beaker, and the residue in the 

 evaporating-dish is completely and carefully removed and added. 

 The liquid is allowed to stand covered for at least eight hours in 

 the cold. Then it is filtered through a small filter, the precipitate 

 washed with alcohol, the filtrate evaporated if necessary until the 

 volume is 50-60 c. c., then allowed to cool and c. c..of an acid- 

 free zinc-chloride solution of an sp. gr, of 1.20 is added ; it is stirred, 

 and the covered beaker is left standing in a cool place for two or 

 three days. The precipitate is collected on a small dried and 

 weighed filter, using the filtrate to wash the crystals from the 

 beaker. After allowing the crystals to completely drain off, they 

 are washed with a little alcohol until the filtrate gives no reaction 

 for chlorine, and dried at 100 C. 100 parts creatinin zinc chloride 

 contain 62.42 parts creatinin. As the precipitate is never quite 

 pure, the quantity of zinc must be carefully determined, in exact- 

 experiments, by evaporating with nitric acid, heating, washing the 

 oxide of zinc with water (to remove any NaCl), drying, heating, 

 and weighing. 22.4 parts zinc oxide correspond to 100 parts crea- 

 tinin zinc chloride. 



