Abstract
In one of his articles, Folin mentions that some preparations of sodium tungstate on the market do not yield a satisfactory reagent for uric acid, presumably because of impurities such as nitrates and molybdates. The tungstate which we have in our laboratory failed to give the reagent although free from the impurities mentioned above. Further investigations, however, disclosed that our sodium tungstate contained but one third tungstate the rest being sodium carbonate. The reagent was therefore prepared in the following manner:
Dissolve 25 g. of sodium tungstate in 300 c.c. of water, heat to boiling in a large beaker, add 40 c.c. of conc. hydrochloric acid whereupon the tungstic acid is precipitated. Continue to boil for ten minutes. Allow to settle. Filter by suction. Wash precipitate with cold water while still in Buchner funnel, 20 c.c. each time, discontinuing as soon as the precipitate starts to pass through the filter, which usually occurs at the third washing. Transfer to an Erlenmeyer flask without drying the precipitate. Add 15 c.c. of 10 per cent. sodium hydroxide solution for each ten g. of tungstic acid, which will dissolve the tungstic acid on heating.
Continue according to instructions given for the preparation of reagent using but 31.2 g. of tungstic acid in place of 100 g. of sodium tungstate as required in the original description of the reagent.
In our search for the explanation of the failure to obtain the reagent we had to limit ourselves to the use of the two tungstates in stock in our store-room; one of them free from carbonate gave the reagent, the other containing carbonate failed to do so. We are postponing the investigation, to determine if any tungstate free from carbonate will react in the desired manner, until the substance is more accessible.
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