Vni] FOODS AND FEEDING STUFFS 81 



11 Indirect Method. — Official. 



Determine the moisture, as directed in 2 or 3, then extract the dried substance 

 for 16 hours as directed under 10, dry again and regard the loss of weight as ether 

 extract. 



Sucrose. 



OPTICAL METHODS. 



1 2 GENERAL DIRECTIONS FOR RAW SUGARS— TENTATIVE. 



(Rules' of the International Commission for Unifying Methods of Sugar Analysis.) 



"In general all polarizations are to be made at 20°C." 



"The verification of the saccharimeter must also be made at 20°C. For instru- 

 ments using the Ventzke scale 26 grams of pure dry sucrose, weighed in air with 

 brass weights, dissolved in 100 metric cc. at 20°C. and polarized in a room, the tem- 

 perature of which is also 20°C., must give a saccharimeter reading of exactly 100.00. 

 The temperature of the sugar solution during polarization must be kept constant 

 at 20°C." 



"For countries where the mean temperature is higher than 20°C., saccharimeters 

 may be adjusted at 30°C. or any other suitable temperature, under the conditions 

 specified above, provided that the sugar solution be made up to volume and polarized 

 at this same temperature." 



"In effecting the polarization of substances containing sugar employ only half- 

 shade instruments." The saccharimeter used can be either single or double wedge 

 and should be a half-shadow instrument with either double or triple field. 



"During the observation keep the apparatus in a fixed position and so far removed 

 from the source of light that the polarizing Nicol is not warmed." 



"As sources of light employ lamps which give a strong illumination such as 

 triple gas burner with metallic cylinder, lens and reflector; gas lamps with Auer 

 (Welsbach) burner; electric lamp; petroleum duplex lamp; sodium light." When- 

 ever there is any irregularity in the sources of light such as that due to the convolu- 

 tions of the filament in the case of electric light or to the meshes of the gauze in the 

 case of the Welsbach light, place a thin ground-glass plate between the source of 

 light and the polariscope so as to render the illumination uniform. 



"Before and after each set of observations the chemist must satisfy himself of the 

 correct adjustment of his saccharimeter by means of standardized quartz plates. 

 He must also previously satisfy himself of the accuracy of his weights, polarization 

 flasks, observation tubos and cover-glasses. (Scratched cover-glasses must not be 

 used.) Make several readings and take the mean thereof, but no one reading may 

 be neglected." Such plates are standardized to read to the second decimal point 

 and by their use a quick and at the same time accurate test can be made. In using 

 such plates for testing saccharimeters, it is necessary that the instrument, as well as the 

 plate, be at 20°C. before making a reading. Different points of the scale, preferably 

 20°, 50°, 80°, and 100°, (sugar scale) should be tested against the plates. 



"In making a polarization use the whole normal weight for 100 cc. or a multiple 

 thereof for any corresponding volume." 



"As clarifying and decolorizing agents use cither basic acetate of lead, alumina 

 cream, or concentrated solution of alum. Boneblack and decolorizing powders are 

 to be excluded." Whenever reducing sugars are determined in the solution for po- 

 larizing, use only neutral lead acetate for clarification as basic lead acetate causes 

 precipitation of some of the reducing sugars. In addition to these clarifying agents, 



