225 



>inl 1-inn/Hirison of effects of varying ijimntitim <>f rltirifi/im/ <i<jmtx on dilution and 



polarization. 



a Sp. gr. 1.259. 



It will he noted that with an estimated dilution of 0.2 cc instead of a decrease in 

 polarization as would be expected there is an increase. With an estimated dilution of 

 0.6 cc the reading is the same as that first obtained, so that the combined effect of the 



dry lead upon the precipitation of levuloe* and upon the lowering of the rotation of 

 fhe lex iil-ise in solution is seen to be most pronounced. It will be noted that when 

 an excess of dry lead is added not til i this passes into solution. Adding 1 gram excess 



caii-cd an increase in the filtrate of only 0.74 gram, and _' L r ram< an increase of only 

 1.8 grams. After the -olution is sufficiently clarilied for reading addition of more 

 I'-ad will continue to form a precipitate, so that the rule of adding lead until no more 

 precipitate forn. d ways a safe one to follow. An interesting fact mthi-. .M 



nection i- that the addition of much lead subacetate beyond the point of maximum 

 darificat ion for low-grade cane products will produce a darkening of the solution. 

 Thi- is due to the well-known color reaction between reducing .-u-ar- and alkalies. 



If the minimum amount of dry lead subacetate necessary to secure satMa< t<>i\ 

 clarification l>e carefully determined for each grade of commercial product and excess 



id this lie avoided there is no <|iieMion but what this method ,f clarification 

 polan . r to the true polarization than any other method thii- far 



pp.po-.-d The DM Q! dr\ I.-.M! -uha tat- and -uhar.-tate >olulin a> d-fecat im; 



agents in the determination of reducing sugars should of course be avoided. 



A third and one of the greatest causes of the hick of agreement in saccharimetrie 

 observations between different chemists is variation in temperature. As regards the 

 effect of temperature U|N>H the polarization of pure sucrose nearly all chemi-t.- an- in 

 lose agreement. l-'..r (juart /.-wedge sacrhari meters the research i-s of Andr.-\\>. 

 Wiley. Schonrock, Watts and Tempany, and other chemists show that for each degree 

 Centiirrade increase in temperature there is a falling off in the polarization of pure 

 sucrose of about 0.031 Ventzke. The question now arises, with this variation in the 

 specific rotation of sucrose with temperature, what correction, if any, should be applied 

 to the polarization of commercial products. 



In my report as associate referee on sugar, made to the association" in 1905, it was 

 shown that the applieation of temperature corrections to low grade cane sugars was 

 not advisable, for the reason that the polarization of a sugar is an expression not 

 merely of the ncroM alone hut of all the optical constituents present and since some of 

 these optical constituents, more especially the levulose, are affected by temperature 

 in a manner contrary to sucrose, it is not permissible to make a temperature correction 

 for one constituent without at the same time correcting for the others. 



This view of the question has been recently contested by Dr. Francis Watts, govern- 

 ment chemist, and Mr. H. A. Tempany, assistant government chemist, for the Leeward 

 Islands of the British West Indies, in a recent number of the West Indian Bulletin. & 



U. S. Dept. of Agr., Bureau of Chemistry, Bui. 99, p. L'<). 

 73673 Bull. 12200 15 



61908, 9: 127. 



