177 



An increa.-e of 0.32 cc in volume by the addition of 2 grams of dry subacetateis 

 noted, ami, with a solution polarizing 81.25, as in the experiment given above 

 tin- -al< -ulaied polarization for this increase in volume would be 80.99. The solu- 

 tion actually polarized 80.9. Home gives 0.22 cc as the increase in volume on 1 

 gram of Hiki.-.-tate. Pellet has shown it to be 0.37 cc. The referee's sugar sample 

 for this year, worked as above described, showed the following changes in volume in 

 two experiments: 



/' * in i nlunie using official sugar samples. 



An average increase in volume of about 0.55 cc is noted, this being due to the pre- 

 cipitate forim-d and also to the fact, as shown above, of the solution of the lead 

 subac. 



From these experiment.- it is seen that clarification with dry lead introduces the 

 same errors an with wet lead, viz, a precipitation of the reducing sugars, and also 

 where u-ed to excess a change iii volume. The latter effect with wet lead acetate as 

 a rlarifier tends to raise the readings while with dry lead there is a tendency to lower 

 tin-in. However, in usim: the dry eubacetate of lead the errors are compensating, 

 the increase in volume tends to lower the reading and the precipitation of the 

 levulose to raise it, while with wet subacetate the volume is decreased by the forma- 

 tion ,,1" the pn-c ipitate. hence the reading increased, and this is again increased by the 

 pre< ipitaiion of the levulose. Dry lead subacetate is a step in advance in the search 

 for the best clarifying agent, and further experiments are in progress; but so far the 

 i clarifying agent for dark-colored sugar solutions has not been found. 



As to the use of hydrosulphites as a bleach for solutions to be polarized there are 

 serious objection*. When large quantities of reducing sugars are present in the sample 

 the reading is lowered. This was pointed out at last year's meeting by the writer. 

 The rotation of one of the sugars, dextrose, is decidedly lowered; hence the 

 polari/ation is lowered if the sample contains much dextrose. This change of 

 rotation of dextrose is due to the formation of an oxysulphonate which has a levoro- 

 tation. The dissociation of the glucose (dextrose) oxysulphonate can be measured 

 by this fact. In the experiments cited no inversion of sucrose by this substance 

 was noted, but later literal ure shows numerous cases of inversion by using commercial 

 hydros ulphite. 



Where the quantity of reducing sugars is small, there is very little reduction in the 

 polarization due to the formation of this compound, and it has this merit, that readings 

 are not vitiated by a change in volume due to a precipitate. These compounds, hydro- 

 sulphites, while stable under most conditions, are very easily decomposed in moist 

 air and also on long standing, and hence lose their power of decolorization. And again, 

 their power of decolorization is limited, as they have no effect on caramel bodies 

 (those which give the dark color to molasses) but do bleach intermediate substances, 

 which on longer heating would yield caramel. 



J. Amer. Chein. Soc., 1907, 29: 928. 



73073 Hull. 1> 09 12 



