226 THE ROYAL SOCIETY OF CANADA 



lead number and malic acid value refer to samples collected over the 

 whole range of maple sugar production. 



Last year in connection with the collaborative work of the 

 Association of Official Agricultural Chemists, Prof. A. G. Woodman, 

 of the Massachusetts Institute of Technology, applied the conduc- 

 tivity method to seven syrups, upon which measurements were also 

 made by Mr. Van Zoeren and myself. For this purpose two sets of 

 directions were issued : First, those of the seventh paper of the series 

 published in the Journal of Industrial and Engineering Chemistry,^ 

 being essentially the original method in which the dilution of the syrup 

 is roughly made; second, the following: 



Weigh out the quantity of syrup containing 22 grams dry matter. 

 Transfer to a 100 cc. volumetric flask with warm water, cool and make 

 up to the mark. Measure 60 cc. of the solution into a 100 cc. beaker, 

 insert a Van Zoeren or other dipping electrode, bring to 25°C. (+0- 1) 

 and measure the electrical resistance. Divide the constant of the cell 

 by the observed number of ohms and multiply the result by 10^. 



The results of this collaborative work, which are given in Table V, 

 suggest that closer agreement might be obtained by use of the second 

 and more precise set of directions, though the results included in 

 Tables III and IV refer to the first and more rapid method. 



The volumetric lead number results are obtained by titrating 

 6 cc. syrup, diluted to 60 cc, with a dilute solution of lead subacetate 

 (sp. gr. 1-033), using electrical resistance measurements to detect 

 the end point. The lead number represents the number of cubic 

 centimeters of lead subacetate corresponding to a break in the curve 

 of resistances. The method has given good results in the hands of 

 both Mr. McFarlane and Mr. Van Zoeren. Using it, Mr. McFarlane 

 has succeeded in discriminating between three pure and four adulter- 

 ated samples, which all gave normal results by all the other methods. 

 The weakness of the method at present consists in the difficulty of 

 deciding on the manner of drawing the curves. The breaks in the 

 curves of genuine syrups are not always as distinct as could be desired. 

 Further work upon this method is in progress and we entertain hopes 

 that in some form it may prove useful. 



The "Canadian" lead method which originated in the Laboratory 

 of the Inland Revenue Department (now the Foods and Drugs 

 Laboratories of the Department of Trade and Commerce) has proved 

 a very useful one and some investigations are in progress in Ottawa 

 and in our own laboratory which may lead to its further improvement. 



1 Journ. Ind. Eng. Chem. 8 (1916), 333. 



