54 2r^^ Philippine Journal of Science i»i6 



the clear titration liquid placed on a test plate gives with a 

 saturated solution of barium hydroxide a distinctly brown rather 

 than white or pale yellow precipitate. To the main portion 

 of the filtrate from the purine bases is added an amount of 

 silver nitrate slightly less than that calculated from the above 

 titration. 



A small aliquot part of the resulting liquid is now titrated 

 with a saturated solution of barium hydroxide. A white pre- 

 cipitate forms, which at first redissolves on stirring. Later 

 the precipitate becomes permanent and gradually darkens. As 

 long as insufficient barium hydroxide is present the precipitate 

 will settle on standing a few minutes, leaving the supernatant 

 liquid bright and clear. Upon the addition of an excess of 

 barium hydroxide the supernatant liquid becomes cloudy or 

 muddy in proportion to the excess of barium hydroxide. Hav- 

 ing thus determined the quantity of barium hydroxide neces- 

 sary, the aliquot part is combined with the main portion and 

 the calculated quantity of barium hydroxide solution is added. 

 A slight deficiency is preferable to an excess. 



The method suggested by Funk of testing with ammoniacal 

 silver nitrate to determine the necessary quantity of barium 

 hydroxide was of very little use to me, as this reagent at no 

 stage produces more than a faint precipitate with the filtrate 

 from the vitamine fraction. 



When the precipitation with barium hydroxide is completed, 

 the precipitate is allowed to settle and after decantation of the 

 clear liquid is collected on a Biichner funnel and is thoroughly 

 washed with water. The precipitate, which has by this time 

 assumed a dark green, is suspended in 100 cubic centimeters 

 of water, into which is led a stream of hydrogen sulphide. 

 The suspension is shaken continuously during the passage 

 of the hydrogen sulphide, which continues for from thirty to 

 forty minutes. The solution is filtered, and the precipitate 

 is repeatedly macerated and washed with small quantities of 

 water containing hydrogen sulphide. The combined washings 

 and filtrate from the silver sulphide are carefully treated with 

 very dilute sulphuric acid until all traces of barium are just 

 removed. After filtering from barium sulphate, the solution is 

 evaporated at room temperature to a volume of 50 cubic cen- 

 timeters. One hundred cubic centimeters of 70 per cent alcohol 

 are added. A rather copious, brown, flocculent precipitate re- 

 sults, which is separated by filtration and washed with 70 per 

 cent alcohol. This precipitate has rather slight curative powers, 



