PRECIPITANTS FOR FURFURAL 



inous precipitate which can be filtered, dried and weighed. As 

 a precipitant for furfural, thiobarbituric acid is superior to 

 phloroglucinol, in that no correction for solubility of the product 

 is necessary. It is also preferable to barbituric acid for the 

 reason that the reaction is quantitative with as small amounts of 

 furfural as 12 mgms. and a large excess of the precipitant is not 

 necessary, thus avoiding possible errors due to inclusion. Un- 

 like the phloroglucinol product, the resulting furfuralmalonyl- 

 thiourea is a definite substance resulting from the condensation 

 of one molecule of furfural with one molecule of thiobarbituric 

 acid by the elimination of one molecule of water, and a definite 

 chemical formula can be assigned to it. It has a further ad- 

 vantage in that the percentages of nitrogen and sulphur, which 

 agree with those calculated from the formula, can be determined 

 by analysis and used as a positive means of identification of the 

 product to distinguish it from, or detect the presence of, similar 

 products which might result in case homologues of furfural were 

 present. For example, if a mixture of furfural and methylfur- 

 fural were precipitated, the determinations of nitrogen and sul- 

 phur on the product should enable us to compute the relative 

 amounts of these two aldehydes, and therefore the relative 

 amounts of pentosans and methylpentosans in the original sample. 

 At present the only means of estimating separately the furfural 

 and methylfurfural present in a mixture such as is frequently 

 met with in analysis, is the supposed differential solubility of their 

 phloroglucides in alcohol, and this admittedly is unreliable. 



It is suggested that thiobarbituric acid, which is not difficult 

 to prepare in a pure state, may be found useful in the analysis 

 of agricultural products, in place of phloroglucinol or barbituric 

 acid, for the determination of pentoses and pentosans. 



LITERATURE CITED. 



(1) Giinther, Chalmot & Tollens, Ber. 24, 3577 (1891). 



(2) Stone, Ber. 24 3019 (1891). 



(3) Flint and Tollens, Ber. 25, 2912 (1892). 



(4) Jolles, Ber. 39, 96 (1906). 



(5) Giinther & Tollens, Ber. 23, 1751 (1890). 



(6) Chalmot & Tollens, Ber. 24, 694 (1891). 



(7) Councilor, Chem. Ztg. 17, 1743. 



(8) Bureau of Chem. Bull. 107, p. 54 (1905). 



(9) Krober, J. Landw. 48, 357. 



(10) Goodwin & Tollens, Ber. 37, 315 (1904). 

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