URINE: QUANTITATIVE ANALYSIS. 



379 



FIG. 121. 



of 97 per cent alcohol and one volume of ether. Stopper the flask 

 and allow it to stand 12-24 hours. Filter off the precipitate, wash it 

 with the alcohol-ether mixture and remove the alcohol and ether 

 from the filtrate by distillation, being careful to keep the tempera- 

 ture of the mixture below 50 C. 1 Treat the remaining fluid (about 

 25 c.c.) with 2 c.c. of hydrochloric acid (sp. gr. 1.124) transfer it 

 carefully to a 200 c.c. flask and evaporate the mixture to dryness on 

 a water-bath. Now add 20 grams of 

 crystallized magnesium chloride and 2 

 c.c. of concentrated hydrochloric acid 

 to the residue and after fitting the flask 

 with a return cooler boil the mixture 

 on a wire gauze over a small flame for 

 two hours. Cool the solution, dilute 

 to 750 c.c. or to 1000 c.c. with water, 

 render the mixture alkaline with potas- 

 sium hydroxide or sodium hydroxide, 

 distil off the ammonia and collect it 

 in an acid solution of known strength. 

 Boil the distillate to remove carbon 

 dioxide, cool and titrate with an alkali 

 of known strength. In this method, 

 as well as in Folin's method (see p. 

 377), correction must be made for the 

 ammonia originally present in the 

 urine and in the magnesium chloride. 



5. Benedict and Gephart's Method. 

 Introduce into a rather wide test- 

 tube or a small Erlenmeyer flask 5 

 c.c. of the urine under examination 

 and an equal volume of dilute (1:4) 

 hydrochloric acid. Cover the mouth 



of the tube or flask with a cap made by folding a piece of lead-foil 

 over the top and place the vessel in an autoclave maintained at a 

 temperature of 150-155 C. for one and one-half hours. 2 After the 

 autoclave has cooled, wash the contents of the tube into an 800 c.c. 

 Kjeldahl distillation flask, dilute the urine mixture to about 400 c.c. 

 with distilled water, add 20 c.c. of a 10 per cent solution of sodium 



1 There is some decomposition of urea at 60 C. 



2 This corresponds to a pressure of about six kilograms per square centimeter. 

 The caps may be conveniently labelled with a stylus. 



FOLIN'S UREA APPARATUS. 



