THE DETERMINATION OF CANE SUGAR 505 



These sources of error are usually summed up in one formxula which 

 may be used as a general one independent of the type of instrument or 

 scale : — 



S20 = Sf + S, 0-0003 (^ — 20). 



This expression is based on the average results of Andrews^'', the U.S. 

 Coast and Geodetic Surv-ey^^, Wiley^^, Geerligs"*", and Watts and Tempany^^, 



The correction quoted immediately above is a blanket correction, and 

 includes the error introduced b\- expansion of the tube, assumed to be glass 

 and of correct length at 20° C. 



The above section assumes that the solutions are observed at the temper- 

 ature at which they were made up. If observed at one and made up at a 

 second temperature the expansion of the sugar solution influences the re- 

 sult, and a correction based on the expansion of the sugar solution, applicable 

 to solutions made up at 20° C. and observed at t° C, must be applied. 



The blanket correction found by Andrews and others agrees exactly 

 with the sum of the individual corrections found bj' Schonrock, referred to 

 25° C. and a nickelin scale. At this temperature the coefficient for sugar is 

 0-000152, which added to 0-000148 gives exactly 0-0003 ^s the blanket 

 correction. Since, however, the temperature coefficient of sucrose is a func- 

 tion of the temperature, a blanket correction can only be correct at one par- 

 ticular temperature. 



The validity of temperature corrections as applied to impure sugars 

 has been ably discussed b)- Browne. ^^ The correction given above is only 

 strictly valid for pure sucrose. Commercial sugars contain fructose, and for 

 this body a reverse correction is necessary. Browne has shown that the 

 correction given in this section is applicable generally to raw sugars of 96 

 test. For sugars containing much reducing sugar it actually accentuates 

 the error, and for sugars of about 80 test he has shown that generally 

 the polarization is independent of temperature, while below this test the 

 correction is negative. Nevertheless, by a decision of the U.S. Supreme 

 Court a temperature correction is applied to all products at the U.S. 

 Customs. This difficulty may be entirely eliminated by making all obser- 

 vations at 20° C. as is done in the New York Sugar Trade Laborator}-. 



The chemist in the tropics has to work at a temperature remote from 

 20° C. Since aU his readings are equally affected, his control and balance 

 sheet are not invalidated. The polarizations of the sugars at northern ports 

 should however be systematically higher than those determined on the 

 plantation, and exact coincidence should be considered as evidence of a 

 deterioration of the sugar in storage and transit. 



Presence of Inactive Bodies. — The most detailed study is due to Fam- 

 steiner*^ who found a small decrease in the specific rotation of cane sugar 

 in the presence of : — 



Hydrates of the alkalies and alkaline earths. 



Chlorides, nitrates, sulphates, carbonates, phosphates, acetates and 

 citrates of the alkalies. 



Chlorides of the alkaline earths. 



Borax, magnesium sulphate. 



An increase occurs with formaldehyde. 



The effect is in all cases small, and in the quantities in which these bodies 

 occur in routine analysis may be neglected. 



The action of lead acetate is discussed separately. 



