R. Newton 



eliiiiinatiug the error clue to the voluiiu' of the precipitate, but also of 

 obviating the necessity of mailing to vohune a second time. The leatl 

 acetate was added in small (juantities at a time, successive small portions 

 of the extract being filtered oft and tested for completeness of precipita- 

 tion. The solution was then filtered through a dry filter paper and 

 deleaded with a minimum quantity of powdered sodium oxalate, fol- 

 lowing the same technique as for clarihcation. A second filtration through 

 a dry filter paper completed the preparation of the extract for sugar 

 analysis. 



Reducing Sugars. The reducing sugars were determined by the very 

 excellent method recently devised by Shaffer and Hartmann (42), in which 

 the cuprous oxide is determined directly by iodo-thiosulphate titration 

 in the presence of an excess of potassium o.xalate. The oxalate inhibits 

 the reaction of cupric ions with soluble iodides. The reduction of Fehling's 

 solution is carried out under the standard conditions prescribed for 

 Miinson and Walker's method (Official Methods, A.O.A.C.) and the sugar 

 corresponding to the quantitv of cuprous oxide read from the tables. 

 By connecting the gas burners witli water manometers, and carefully 

 calibrating them in conjunction with the flasks used for the reductions, 

 it was found possible to keep within 10 seconds of the four minutes 

 prescribed for bringing the solution to boiling. 



The thiosulphate was standardised against pure copper by an ada[)ta- 

 tion of the simple method proposed by Peters (36). Triplicate standardisa- 

 tions by this method varied less than ()•(>] mg. copper per c.c. N/10 thio- 

 sulphate. 



The accuracy of this sugar method was tested witii pure dextrose 

 obtained from the Bureau of Standards. Duplicate portions of 100 mg. 

 and of 150 mg. of the anhydrous sugar were weighed out. dissolved in 

 water and carried through the analytical {)rocedure, with the following 

 results : 



The nuijority of the sugar determinations made fell within the limits of 

 these quantities. Aliquots of 10 c.c. of the cleared extract were used 

 for the reductions. 



Sucrose. The sucrose was determined by the increase in reduction 

 on inversion of the cleared extract. For inversion the citric acid method 

 of Davis and Daish(8) was employed. Comparative tests with invertase 



