1 68 PHYSIOLOGICAL CHEMISTRY. 



Ether Extract. Evaporate this solution on a safety water-bath 

 until the ether has been entirely removed. Extract the residue with 

 warm water and filter. 



Aqueous Solution. Evaporate this solution until crystallization 

 begins. Stand the solution in a cold place until no more crystals 

 form. This crystalline mass consists of impure leucine and tyro- 

 sine. Filter off the crystals. 



Crystalline Deposit. Examine the crystals under the microscope 

 and compare them with those reproduced in Figs. 23, 26 and 104, 

 pages 72, 76 and 350. Do the forms of the crystals of leucine and 

 tyrosine resemble those previously examined? Make a separation 

 of the leucine and tyrosine and apply typical tests according to 

 directions given on pages 83 and 84. 



Filtrate No. I. Make a test for tryptophane with bromine water 

 (see page 145), and, also with the Hopkins-Cole reagent (see page 

 91). Use the remainder of the filtrate for the separation of pro- 

 teoses and peptones. Make the separation according to the direc- 

 tions given on page 114. 



Filtrate No. 2. This solution contains para-oxyphenylacetic acid, 

 para-oxyphenylpropionic acid and skatole-carbonic acid. Prove the 

 presence of these bodies by appropriate tests. Tests for oxyacids 

 and skatole-carbonic acid are given on page 171. 



TESTS FOR VARIOUS PUTREFACTION PRODUCTS. 



Tests for Indole. 



i. Herter's /?-Naphthaquinone Reaction. (a) To a dilute 

 aqueous solution of indole ( I : 500,000} add one drop of a 2 per 

 cent solution of /3-naphthaquinone-sodium-monosulphonate. No 

 reaction occurs. Add a drop of a 10 per cent solution of potassium 

 hydroxide and note the gradual development of a blue or blue-green 

 color which fades to green if an excess of the alkali is added. Ren- 

 der the green or blue-green solution acid and note the appearance of 

 a pink color. Heat facilitates the development of the color re- 

 action. 



One part of indole in one million parts of water may be detected 

 by means of this test if carefully performed. 



(b) If the alkali be added to a more concentrated indole solu- 

 tion before the introduction of the naphthaquinone the course of 

 the reaction is different, particularly if the indole solution is some- 



