440 ALBUMINOUS COMPOUNDS. 



to make up a litre. Pour it into a large well-stoppered bottle, 

 taking care that there is no ammonia near it at the time. It 

 will deposit a In-own precipitate, and become quite clear and 

 of a pale greenish-yellow color. It is then ready for use ; a 

 little of it should be poured into a smaller bottle when wanted. 



37. Detection of Leucine in Tissues. In order to de- 

 tect the presence of leucine, cut up the organ (the pancreas of 

 a, sheep or ox, for example) into small pieces with a large knife 

 or Bansftge-makiDg machine. Mix it with water and let it stand 

 for a littte while, stirring it frequently ; filter it through a piece 

 of cloth, and press out the water first with the hand, and then 

 with a screw-press. Extract it with water a second time in the 

 same way. Mix the watery extracts together, acidify slightly 

 with acetic acid, and boil, to coagulate the albumin. Filter: 

 add a solution of lead acetate to the iiltrate. Filter : pass sul- 

 phuretted hydrogen through the filtrate to remove the excess 

 of lead. Filter: evaporate the filtrate to dryness. Extract 

 the residue with boiling alcohol. Filter: evaporate the filtrate 

 to a syrup, and set it aside for several days to crystallize. If 

 leucine is present, it will crystallize in a day or two in balls or 

 knots, or, possibly, in shining plates, but will not form good 

 crystals. It is not pure, but is mixed with a number of other 

 substances. In order to free it from these, the following- method 

 is recommended by lloppe-Seyler. Dissolve it in ammonia, 

 add lead acetate till no further precipitate is produced. Filter: 

 wash the precipitate with a little water. Suspend it in water, 

 and pass sulphuretted hydrogen through it. Filter, and 

 evaporate the filtrate in the water bath. 



38. Tests for Leucine. The formation of round lumps or 

 plates is not suttieient to prove that a substance is leucine, and 

 other tests must be applied to them. Before doing so, they 

 should be purified by drying them between two folds of blot- 

 ting-paper, dissolving them in boiling alcohol, and letting them 

 crystallize out again. The following tests may be applied: 



1. Tut a portion into a dry test-tube and heat it over a 

 P.unsen's burner or spirit-lamp. If it consists of leucine, it 

 will emit the smell of amylamine. 



-2. SHieivr's Test: Put a small portion of the supposed 

 Icuciiie with a drop of nitric acid on a piece of platinum foil, 

 and evaporate it gently. If it is pure ieucine, a colorless, 

 almost invisible, residue will remain on the foil. Add a few 

 drops of liquor potas>;e to it, and heat. It will become yellow 

 or brownish, and then form an oily drop, which runs 'about 

 upon the foil without adhering to it. 



39. Tyrosine. 7'/v/ifm///o/j. Boil horn shavings with 

 dilute sulphuric acid, crystallize out the tyrosine, as directed 

 in the preparation of leucine, wash the crystals with cold 



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