and gives zero or negative results, as indicated by the following com- 

 parisons of lead numbers on two series of sirups calculated from both 

 unfiltered and filtered standards. 



Comparison of lead numbers on two series of known mixtures, using unfiltered and filtered 



standards. 



On another lead subacetate solution the standard was obtained in 

 three ways. First, on the unfiltered blank; second, on the filtered 

 blank; and, third, on a blank to which 25 grams of a cane sugar sirup 

 were added prior to the addition of the 25 cc of lead subacetate solu- 

 tion. The weights of lead sulphate obtained from 10 cc aliquots were 

 respectively 0.1701 gram, 0.1660 gram, and 0.1685 gram. If the 

 filtered blank is taken as the standard, one would apparently obtain 

 more lead from the cane sugar sirup blank than was actually added, 

 which discrepancy is corrected by the use of the unfiltered blank. 

 To avoid the possibility of obtaining an incorrect aliquot on the 

 turbid unfiltered blank, add 5 cc of 10 per cent acetic acid to the 

 blank flask prior to the addition of the 25 cc of lead subacetate 

 solution, which insures a clear blank for the determination of the 

 standard. 



Acetic acid should be added only to the blank, since this reagent 

 dissolves the maple lead precipitate. Otherwise the procedure was the 

 same as given by Winton with the exception that after addition of 

 lead subacetate the mixture was allowed to stand three hours prior 

 to filtering; 2 cc of 20 per cent sulphuric acid were used to precipitate 

 the lead. The results were calculated by subtracting the weight of 

 the lead sulphate obtained from 10 cc of the clear filtrate from that 

 obtained from 10 cc of the acidified blank or standard. The re- 

 mainder expressed in grams multiplied by 27.325 a equals the lead 

 number or percentage of lead precipitated by the sirup. 



FURTHER STUDY OF KNOWN MIXTURES, USING THE ACID BLANK. 



The lead number was determined on four straight sirups, and on 

 four series of mixtures made by combining with each sirup various 

 percentages by weight of S (cane sugar sirup, 66 per cent sucrose 



This factor is obtained by dividing the lead factor (0.68312) by the number of 

 grams of sirup in the 10 cc used (2.5 grams) and multiplying by 100. 

 [Cir. 53] 



