45 



first may be determined the percentages of, first, cane sugar ; second, 

 grape sugar, otherwise called glucose; third, " not sugar; " fourth, water; 

 constituting the juice. By the second method, the cane sugar alone is 

 determined. The optical method is, however, conveniently used in con- 

 nection with the chemical, in making complete analyses. One of the 

 chemical methods will be considered first. I shall go as little as possi- 

 ble into teclmicality'here. 



FEHLING'S SOLUTION OF COPPER. 



This is the principal reagent used in the chemical methods of analy- 

 sis. There arc several modifications of it. Perhaps none of these is 

 better than Violette's solution : * 



34.64 grams pure crystallized copper sulphate. 



184.00 grams tartrate soda and potash (Rochelle salt). 

 78.00 grams caustic soda. 



The copper salt is to be dissolved in 140 cubic centimeters of distilled 

 water, slowly added to a solution of the tartrate and caustic soda, and 

 the .whole made up to 1 liter at standard temperature (17 Centigrade ; 

 63 J Fahrenheit). This should be a clear blue solution, 



THE GRAPE-SUGAR TEST. 



If now a portion of this copper solution be brought to a boil, and to 

 it be added a solution containing grape sugar, the blue color will be 

 changed through various shades of purple to crimson, and finally to 

 scarlet. The reaction has reached the decisive stage when the color is 

 crimson. On standing, the crimson precipitate settles to the bottom of 

 the vessel. This is the reaction for the determination of grape sugar. 

 If a definite quantity, say 10 cc., of the copper solution be used in the 

 above experiment, a definite quantity of grape sugar, .05 grams, will 

 have to be added to perfect the reaction. Now by noting the amount 

 of sample added to complete the reaction, the determination of the per- 

 centage of grape sugar from the experimental data becomes a mere 

 matter of arithmetic. Thus, if 4 grams of the sample had been added 

 to produce the complete reaction, we should have known that those 4 

 grams of sample contained fi ve-hundredths of a gram of grape sugar. 

 .05 -f- 4 =.0125, or 1J per cent, of grape sugar. 



THE CA]NE SUGAR TEST. 



Cane sugar has no such effect on the copper solution. It has been 

 remarked already that cane sugar changes very readily into grape 

 sugar. This change is easily produced by boiling the solution of cane 

 sugar; for example, the cane jtiice with dilute hydrochloric or sulphuric 

 acid. The cane juice will now contain the grape sugar it originally con- 

 TI i-k era Sugar Aualyais, p, 186, 



