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IOWA ACADEMY OP SCIENCE 



theory. The last two determinations above show that the reaction 

 should not be allowed to occur at a high temperature since this 

 leads to results that are too low. 



TABLE III. 

 MALONYLGUANIDINE. 



The condensation of furfural with malonylguanidine is not 

 quantitative. The yield in the two determinations quoted above 

 was only a little more than half the theory, hence under these 

 conditions malonylguanidine is not applicable for the quantita- 

 tive determination of furfural. 



Having shown that thiobarbituric acid in moderate excess gives 

 quantitative results under the conditions of the above exjoeri- 

 ments, whereas barbituric acid under the same conditions gives 

 less than 95 per cent of the theoretical yield, it remains to com- 

 pare these two reagents as regards their sensitiveness to smaller 

 amounts of furfural. In the determinations recorded in table 

 IV, four times the theoretical amount of barbituric acid was 

 used. 



TABLE IV. 

 BARBITURIC ACID. 



It is obvious therefore, that the barbituric acid method is in- 

 applicable to the determination of small quantities of furfural. 



In table V, varying amounts of furfural are treated with vary- 

 ing amounts of thiobarbituric acid. 



