538 THE SECRETIONS. 



centimetres. Then add hydrochloric acid, and set aside until 

 next day. A large quantity of hippuric acid will have separa- 

 ted in the form of a brown crystalline mass. Wash with cold 

 water, press the crystalline mass between folds of filtering 

 paper ; dissolve in as little boiling water as possible, add a 

 little pure animal charcoal (i. e., animal charcoal which has 

 been in contact with dilute hydrochloric acid for many daj T s, 

 and then thoroughly washed with water), and filter. The 

 filtrate should be concentrated and allowed to crystallize. 

 ( l-'or other methods of separating hippuric acid, especially 

 when existing in small quantities, the reader is referred to 

 Hoppe-Seyler's " Handbuch der physiologisch- und patholo- 

 gisch-chemiBchen Analyse, 1870, p. 15Y). 



Having obtained nearly pure hippuric acid, the following 

 experiments may be tried : 



1. Dissolve a fragment in boiling water, and allow a drop 

 of the solution to crystallize on a microscope slide. The acid 

 usually separates in the form of transparent prisms which are 

 single, or occur in radiating groups, and generally present four 

 sides parallel to their long axis ; their ends are terminated by 

 two or four planes. Their primary form is a right rhombic 

 prism (fig. 313). 



2. Heat a fragment of hippuric acid in a small glass tube, 

 with a little soda-lime ; the ammonia which is given off, and 

 which can readily be detected by its odor, proves that the body 

 under examination contains nitrogen. 



3. Mix a fragment of hippuric acid with strong nitric acid 

 in a small porcelain crucible. Boil and then evaporate to 

 dryness; on heating the residue, a very characteristic odor of 

 nitro-benzol is developed. 



* 188. Separation of Creatinine (C 4 H.N 3 O) from 

 Urine. To 300 cubic centimetres of urine add milk of lime 

 until the reaction of the fluid is decidedly alkaline. Then add 

 a solution of chloride of calcium as long as a precipitate falls. 

 After the precipitate has been allowed partially to subside, 

 filter, evaporate the filtrate to dryness in a basin or the water- 

 ball), and add to the yet warm residue thirty or forty cubic 

 centimetres of 95 per cent, alcohol. Stir and decant the con- 

 tents of the basin into a beaker, taking care to add the alco- 

 holic washings of the basin. Set aside the beaker in a cool 

 place. Filter and wash the insoluble residue with a little more 

 spirit. If the filtrate and washings amount to more than 50 

 c. c,, concentrate at a gentle heat to that volume. Allow the 

 fluid to cool, and then add half a cubic centimetre of an alco- 

 holic solution of chloride of zinc, absolutely free from the least 

 t rare of acid, and stir for some time. Set the beaker aside for 

 three or four days in a cellar. At the end of that time the' 

 whole of the creatinine will have separated in combination 



