44 IOWA ACADEMY OF SCIENCE 



lized out. The yield was about 30 per cent of the theory. In 

 preparing a further quantity of thiobarbituric acid we found 

 that a much better yield was obtained when less solvent was 

 used and the mixture heated for 15 hours in a sealed tube at 

 105°, with twice the theoretical amount of sodium, as recom- 

 mended by Fischer and Dilthey 20 in their preparation of methyl- 

 ethyl and dimethylthiobarbituric acid. The product, after 

 acidifying with hydrochloric acid, was a slightly yellowish crys- 

 talline powder containing 19.61 per cent nitrogen, whereas the 

 theory calls for 19.45 per cent. The yield in this case was 45 

 per cent of the theory. 



Malonylguanidine was made according to Traube from free 

 guanidine and malonic ester. The condensation took place read- 

 ily and gave an excellent yield. The product was used directly 

 without further purification. It contained 32.07 per cent nitro- 

 gen; theory, 33.06 per cent. 



Parallel determinations were now conducted, using barbituric 

 acid, thiobarbituric acid and malonylguanidine as precipitants 

 for furfural. For this work a stock solution of pure, freshly 

 distilled furfural of exactly 1 per cent strength was prepared, 

 and a 5 cc. aliquot taken for each determination. The furfural 

 was diluted with 12 per cent hydrochloric acid and solutions 

 of the different precipitants in 12 per cent hydrochloric acid 

 added, the total volume of the reaction mixture being 400 cc. 

 The conditions were, therefore, similar to those obtaining in 

 pentosan determinations. Unless otherwise indicated, a slight 

 excess of the precipitant was employed, the reaction carried 

 out at room temperature, and the precipitate allowed to stand 

 over night before filtering on Gooch crucibles and drying to 

 constant weight at 100°. The analytical results are set forth 

 in the following tables : 



