CHOLINE 49 



more barium carbonate comes down. Filter and evaporate the 

 filtrate to dryness. Treat the residue with absolute alcohol, 

 which will dissolve the choline but not the barium glycero- 

 phosphate. The alcoholic solution, if treated with an alcoholic 

 solution of platinic chloride, gives a precipitate of the double 

 platinichloride of choline. 



Green and Jackson * give the following method : Allow the 

 finely divided material to stand for some days under absolute 

 alcohol. Pour off the extract, and evaporate to dryness ; the 

 residue is again extracted with absolute alcohol, and finally 

 with a mixture of alcohol and ether. These extracts are 

 mixed, and the solvents evaporated off. The choline is con- 

 tained in the residue. The following tests may be employed 

 for its detection : 



1. Boil a strong aqueous solution ; decomposition ensues 

 and trimethylamine is given off, which may be recognized by 

 its fish-like smell. 



HON(CH 3 ) 3 CH a CH 2 OH = OHCH*CH 2 OH + N(CH 3 ) 3 



Choline Trimethylamine 



2. Add platinic chloride to the aqueous solution ; a double 

 platinum salt is formed, which crystallizes on standing. The 

 crystals are soluble in 1 5 per cent alcohol. Should the crystals 

 not appear, proceed as follows : 



3. Dissolve choline in alcohol and add an alcoholic solution 

 of platinic chloride. Filter off the yellow precipitate, wash 

 with alcohol and dissolve in as little water as possible. Place 

 the solution in a watch glass, and stand in a desiccator. , Hex- 

 agonal plates will be deposited. 



4. In order to detect very small quantities, Rosenheim 

 recommends the following method. f Prepare the double plati- 

 num salt, place a drop or two on a glass slip, and allow to 

 evaporate. Add a drop of a solution containing 2, grams of 

 iodine and 6 grams of potassium iodide in 100 c.c. of water, 

 and examine under the microscope. Dark brown prisms or 

 plates will appear and then disappear as evaporation takes 

 place ; they will reappear on adding another drop of iodine 

 solution. 



* Green and Jackson : " Proc. Roy. Soc., Lond.," B., 1906, 77, 69. 

 t Rosenheim: " J. Physiol.," 1905, 33, 220. 



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