CANE SUGAR. 



beatable prisms, as made by the firm of Zeiss, of Jena. Tbe determination of 

 tbe refractive index is made as follows : The instrument is brought into a 

 horizontal position, and the two prisms A and B separated by opening the 

 milled head clamp ai p ; a drop of the material under analysis is placed on one 

 of the prisms, which are then closed and secured by the clamp so as to obtain 

 a film of material ; the mirror R is then adjusted so as to throw a beam of 

 light through the prisms; looking through the observation telescope at and 

 moving the alidade S on the left of the instrument, a dark shadow is seen to 

 move over the field. The reference point is the coincidence of the edge of the 

 shadow with the intersection of cross lines in the field of vision ; the reading 

 on the quadrant scale J gives directly the refractive index of the material 

 under examination, whence can be obtained the percentage of dry matter from 

 reference to the tables, given in the Appendix. 



To maintain a constant temperature a stream of water should be allowed 

 to pass through the coil D E, arranged in the instrument. 



The milled head M on the right of the base of the observation telescope 

 serves to correct for colour ; when not adjusted, instead of a uniform dark 

 shadow a coloured shadow appears, the dark shadow being obtained by rotation 

 of the milled head. 



In the Appendix is given a table connecting refractive index and per cent. 

 of solids as arranged by Peck from Geerligs' data. 



Determination of Ash. The determination of the ash of sugar 

 products offers no difficulties ; the incineration is best performed in a platinum 

 dish at a low red heat to prevent any volatilization of potash ; as the sugary 

 materials swell greatly on heating, the dish used must be capacious and the 

 heating gradual. 



It has been the custom with sugar analysts to determine the ash after a 

 preliminary carbonization with sulphuric acid, and to correct for the increase 

 in weight by deducting 10 per cent, from the recorded weight. This process 

 is of course inaccurate, and, so far as regards the sugar materials the writer 

 has encountered, unnecessary ; the preliminary carbonization is claimed to 

 render the materials more readily combustible. 



Determination of Cane Sugar. 1. In the Absence of Reducing 

 Sugars. Weigh out a definite weight of material in a suitable vessel, such as 

 the German silver vessels sold by dealers for this purpose ; transfer to a flask 

 graduated at 50 c.c. or 100 c.o., and clarify by one of the methods given in 

 Chapter XXII. ; make up to the mark, filter and take the polariscope reading ; 

 then if the material be dissolved in 100 c.c , and if the 20 cm. tube be used 



the percentage of sugar is given by the expression =- where R is the 



observed reading, N is the normal weight of the polariscope used, and W is 

 the weight of the material used. 



474 



