44 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



To invert a pure 0*5 per cent, sucrose solution, these 

 workers found it sufficient to boil for ten minutes with 

 2 per cent, crystalline citric acid, and their analyses by 

 Ling's solution substantiate this statement. However, 

 Davis and Daish pointed out that the sodium acetate 

 usually present in de-leaded plant extracts so lessens 

 the ionization of citric acid as to require a concen- 

 tration of 10 per cent, to effect inversion by boiling for ten 

 minutes. This 10 per cent, is over and above an addition 

 of sufficient sulphuric acid to cause the solution to have a 

 faintly acid reaction to methyl orange. 



ESTIMATION or MALTOSE. 



Experiments with maltose showed that digestion of 

 25 c.c. of a dilute solution with 1 c.c. of autolyzed yeast 

 for three hours at 40 did not result in the hydrolysis of 

 any of this sugar. Treatment with 10 per cent, citric acid 

 produced slight hydrolysis, of the order of 1 per cent. In 

 the presence of sodium acetate and sulphuric acid, as before 

 described, the hydrolysis is considerably less. In their 

 analyses, however, they adopted both the invertase and 

 citric acid methods of hydrolysis for sucrose, and thus 

 obtained a double check on their accuracy. Both the 

 Clerget and Herzfeld conditions result in the hydrolysis of 

 considerable quantities of maltose, so they were not em- 

 ployed. Kluyver (1914) has stated that this criticism of 

 the Herzfeld method is not justified, but Davis in his reply 

 (1914) has completely upheld his own position. 



The action of hydrochloric acid upon maltose was very 

 exhaustively studied by Davis and Daish, for, as is well 

 known, only 98 to 99 per cent, of the theoretical yield of 

 d-glucose is obtainable owing to the formation of levulinic 

 acid and humus substances. As a result of their work 

 with various concentrations of acid and at several tempera - 



