THE DETERMINATION OF CANE SUGAR 517 



Method of performing the Inversion. — The methods of performing the 

 inversion accepted as standard are many. They have been critically ex- 

 amined by Jackson and Gillis, and the following section is based largely 

 on their work. 



The original Clerget method of inversion was to place 50 c.c. of the 

 material to be examined in a 50-55 c.c. flask, fill to the 55 c.c. mark with 

 strong hydrochloric acid, heat to 68° C, taking 15 minutes to reach this 

 temperature, allow to cool and polarize, adding 10 per cent, to the result or 

 using a tube 10 per cent, longer than that used in the direct polarization. 

 This method has always been used in France and is the one preferred by 

 Browne. In 1883 the original procedure of Clerget was modified thus by 

 Herzfeld". Into a 100 c.c. flask, 50 c.c. of the material from the direct 

 polarization is placed together with 20 c.c. water and 5 c.c. of 38 per cent, 

 hydrochloric acid, sp. gr. i-i88. The flask and its contents are then heated 

 to 67° C, taking 2-5 to 3 minutes to reach this temperature, which is after- 

 wards kept as near as possible at 69° C. for 5 minutes and always between 

 the limits 67 — 70° C. After cooling rapidly and completing to 100 c.c, the 

 reading is observed. 



These directions are frequently misquoted, acid of 38-8 per cent, strength 

 sp. gr. 1-1198 being specified, and the total time of heating being extended to 

 10 minutes. 



Jackson and GiUis'® have shown that this routine is unsound since dupli- 

 cates cannot be obtained, and since after a maximum value of a has been 

 obtained its value falls so rapidly with continued heating that unavoidable 

 deviations from one determination to another invalidate results. They 

 show a maximum, constant with large deviation from the stipulated time, 

 can be obtained by their method (a), or that of Walker [h) : — 



(a) .Seventy-five c.c. of material and five c.c. of 38-8 per cent, acid are 



placed in a water bath kept at 60° C, agitated for three minutes 



and allowed to remain in all for six minutes. If 10 c.c. of acid 



diluted I : i and 70 c.c. material are used, the total time of 



exposure is increased to 9*5 minutes. 

 {b) Seventy-five c.c. of material are placed in a flask and heated to 



65° C, followed by the addition of 5 c.c. of 38-8 per cent. acid. 



The inversion is complete after 15 minutes' standing without 



further heating. 



Methods employing inversion in the cold are in use and Tolman'' pro- 

 babh' first proposed them, using 5 c.c. of strong acid to 50 c.c. of material and 

 allowing 10 hours at 26° C. and 20 hours at 20° C. for inversion. Steuerwald'^ 

 used 30 c.c. of acid 1-1029 ^P- gr. (38-8 per cent, acid diluted i : i) and 

 prescribed 2 hours' exposure if the temperature was 25° C. or over, and 3 

 hours if below 25° and above 20° C. Jackson and Gillis, for a total volume 

 of 80 c.c. with 5 c.c. of 38-8 per cent acid, demand 30-8 hours at 20° C, 

 14-6 hours at 25° C, 7-1 hours at 30° C, 106 minutes at 40° C, and 29 

 minutes at 50° C. With 55 c.c. total volume and 5 c.c. 38-8 per cent, acid, 

 the times are 21-2 hours at 20° C. and 10 hours at 25° C. 



Concentration of the Acid. — The rotation of invert sugar varies with the 

 concentration of the acid, and accordingly there will be found different con- 

 stants depending on the concentration of the acid in material as presented for 

 observation. The value found by Clerget, 16 grams sucrose and 5 c.c. strong 

 acid, in a total volume of 55 c.c, was 1-44. The value under Herzfeld's pro- 



