384 PHYSIOLOGICAL CHEMISTRY. 



membering that i c.c. of -^ sulphuric acid is equivalent to 0.0179 

 gram hippuric acid. 



2. Gravimetric Determination. The urea- free ethyl acetate so- 

 lution, contained in the separatory funnel, after washing with 

 sodium chloride solution, as described under Preliminary Procedure, 

 p. 383, is washed with 5 c.c. of distilled water to remove the major 

 portion of the sodium chloride. Transfer the solution from the 

 separatory funnel to a round-bottomed flask and subject it to a steam 

 distillation in the usual way. A slow current of steam should be 

 used while the ethyl acetate is being distilled off and later a more 

 rapid current may be employed. The distillation should be con- 

 tinued for twenty minutes. Now add about o.i gram of charcoal 

 to the aqueous solution which is heated to boiling and filtered hot. 

 Evaporate the solution in a weighed Jena glass dish on a water-bath 

 until the volume of the solution is reduced to about 3 c.c.. Stand 

 the dish in a warm place until evaporation is complete and a crys- 

 talline residue remains. Wash the residue, in turn, with 2 c.c. of 

 dry ether, and I c.c. of water, dry it in an air-bath at 100 C. and 

 weigh. If it is so desired the residue may be recrystallized from a 

 little hot water and the melting-point determined. Pure hippuric 

 acid melts at 187 C. Contamination with phenaceturic acid may 

 be detected both by the melting-point and the microscopical char- 

 acteristics. 



VIII. Sulphur. 



i. Total Sulphates. Foliris Method. Place 25 c.c. of urine 

 in a 200-250 c.c. Erlenmeyer flask, add 20 c.c. of dilute hydrochloric 

 acid 1 (i volume of concentrated HC1 to 4 volumes of water) and 

 gently boil the mixture for 20-30 minutes. To minimize the loss of 

 water by evaporation the mouth of the flask should be covered with 

 a small watch glass during the boiling process. Cool the flask for 

 2-3 minutes in running water, and dilute the contents to about 150 

 c.c. by means of cold water. Add 10 c.c. of a 5 per cent solution of 

 barium chloride slowly, drop by drop, to the cold solution. 2 The 

 contents of the flask should not be stirred or shaken during the ad- 

 dition of the barium chloride. Allow the mixture to stand at least 



1 If it is desired, 50 c.c. of urine and 4 c.c. of concentrated acid may be used 

 instead. 



2 A dropper or capillary funnel made from an ordinary calcium chloride tube 

 and so constructed as to deliver 10 c.c. in 2-3 minutes is recommended for use in 

 adding the barium chloride. 



