174 



Polarizations of sugar with different clarifying agents, using only amount necessary for 



clarification Continued. . 



BASIC LEAD NITRATE (HERLES' SOLUTION). 



ALUMINA CREAM AND SODIUM HYDROSULPHITE. 



Average. 



92.75 .. 



94.11 



o Not included in average. 



The results of individual analysts on direct polarization compare very favorably 

 in each method of clarification. There are, however, some higher figures than the 

 average, but. in every case the polarization was carried on at a lower temperature or 

 an excess of the precipitant was used. With a few exceptions the results on sucrose 

 by the Clerget method do not differ so widely as the direct polarizations. This differ- 

 ence with the Clerget method is most likely due to the different methods of inverting 

 or to an error in calculation. As a check for the first error it is well to run a test on 

 pure sucrose with each set of determinations. This is especially wise in case of invert- 

 ing by heat, as the temperature may not be right or the time either too short or too 

 long, and, as a result, either all the sucrose has not been inverted, or the inversion has 

 been carried on so far that reversion products have been formed. Even in the stand- 

 ing method for inversion this blank is valuable in determining the completeness of 

 the inversion. There is a point in the cold inversion that should receive some atten- 

 tion. This is the question of the relation of time and temperature. In a few experi- 

 ments on the same sugar solution, one inverted by standing at 20 C. for twenty 

 hours showed 12.3, while the other portion by standing at 32 for twenty hours 

 showed 12.08. These figures would make a difference in the Clerget sucrose. 



The other point, error in calculation, is one that for some reason or other is rather 

 common. The inversion is carried on by taking 50 cc of the solution and adding 

 5 cc of acid and not correcting the reading for the increase of 10 per cent in volume. 

 Chemists not using the formula often should guard against this error, as the difference 

 amounts to nearly 3 per cent in high polarizations. 



In comparing the average results of direct polarization it is noted that hydrosul- 

 phite gives the lowest reading, while wet subacetate gives the highest. The normal 

 acetate and Herles' solution give nearly the same results. Dry subacetate gives 

 readings that are lower than the two above mentioned and stands next to hydro- 

 sulphite. 



