THE DETERMINATION OF CANE SUGAR 515 



Deerr's Method. — On the plate of a Buchner funnel is placed a layer of 

 glass wool, after which the funnel is filled with the massecuite under analysis. 

 On connecting to the vacuum, the molasses, entirely freed from crystals, 

 passes through. 



Let X and y be the proportions of sugar in the massecuite and filtered 

 molasses, respectively, and let s be the proportion of sugar as cr3'stals per unit 

 of massecuite. 



Then x ■— ii — s) y + s, whence s = -. 



1 — y 



This equation gives the amount of crystals of pure sugar ; actually, in 

 practice, the crystals are obtained with an adhering layer of molasses, which 

 increases the weight, as indicated by this analysis. 



These methods have been described as applicable to massecuites ; they 

 are, of course, applicable to molasses to determine the quantity' of fine grain 

 which has been separated on cooling, or is present after having passed through 

 the mesh of the centrifugal basket. 



Detection and Estimation of Small Quantities of Sugar. — The reaction 

 of Molisch'^^ is the one most often used. It is thus carried out : — Five 

 c.c. of concentrated sulphuric acid are placed in a test tube, into which 

 is then run 2 c.c. of the water supposed to contain sugar, followed by 

 the addition of two or three drops of a 5 per cent, alcoholic solution of 

 a-naphthol ; the contents of the test tube are shaken, and the colour 

 produced compared with that obtained with known quantities of sugar ; 

 as little as one part of sugar in 1,000,000 can be detected. If the sul- 

 phuric acid alone produces the reaction it should be boiled to destroy 

 organic matter before use. 



Ammonium molybdate is also a useful re-agent to employ, and, as shown 

 by Pinoff,''^ is specific for fructose in the absence of mineral acids. As 

 applied by Pinoff to fructose o-i gram of material, 10 c.c. of a 4 per cent, 

 solution ammonium molybdate, 10 c.c. water and 0-2 c.c. glacial acetic acid 

 are heated at 95° C. ; fructose in three minutes gives a fine blue coloration ; 

 all sugars give the same reaction in the presence of mineral acids. The 

 writer modifies this test as follows : — To a suspected water 2 per cent, of 

 hydrochloric acid of i • 18 sp. gr. is added, placed in a test tube, and heated 

 on the water bath for five minutes ; an equal quantity of a 5 per cent, 

 solution of ammonium molybdate is then added, and the heating continued 

 for five minutes ; in the presence of sugars a blue coloration is produced, 

 which may be compared with previously prepared samples. The colour 

 thus produced may be simulated by solutions of copper sulphate prepared 

 to represent the coloration produced by i part of sugar in 20,000, etc. 



The sugar in waste waters and condenser water may be also conveniently 

 estimated by evaporating a large quantity, say, two litres, to a volume of 

 100 c.c. and determining the sugar by the polariscope or by ascertaining the 

 reducing sugars after inversion. 



In making the calculations, the quantity of water used in the condenser 

 is estimated from the difference in temperatures of the incoming and outgoing 

 water combined with a knowledge of the quantit}^ and pressure of the steam 

 given off in the last body. The experiments of the writer (cf . Chapter XVIII) 

 have shown that the steam given off in the last body is nearly i /«th of the 

 total evaporation, where n is the number of units. 



