478 SORGHUM. 



Calling the value of the sucrose, as found by analysis, 100, the value 

 indicated by the p^lariscoj^e -was 94.87 for the maize, and 95. 9G fir the 

 sorghum. The nearly caustant diiTcrcnce of ab:nit 4 per cent le.-s su- 

 crose, as determined by these polariscope tests, than was found by cu- 

 prous precipitation, was, f)r the time, att!-i])utcd t) a portion t^f invert 

 sugar, and to various causes, whic!i i)robably were misconceptions, see- 

 ing that this discrepancy disappears almost entirely in the results of 

 1882, viz.: Number of analyses and polarizations 517, of some forty 

 varieties of sorghum. 



Total polarization, 5,440.76; average percentage, 10.524. 



Total by analysis, 5,433.72 ; average percentage, 10,510. 

 10.510:10.524 = 100:100.13. 



Each result of the 517 is of record, hut the general result given 

 suffices. The conclusion seems justified, that any differences existing in 

 the polarization and analyses with normal fresh juices, are only differ- 

 ences incidental t > the work, and are not caused by any active rotatory 

 substance present other than sucrose. If the juice is abnormal, very 

 wide differences may exist. This was conspicuous in the mill work at 

 tlie department in 1881, both in juices and syrups. 



The comparisons in 1879-1881, between large numbers of deter- 

 minations, by the cuprous precipitation and by i)olariscope, appeared 

 to sustain the opinion that there was a pretty constant difference iu 

 favor of the volumetric method, i. e., that the polariscope, for some 

 unknown reason, failed to detect as much sugar as was demonstrated 

 by the method of precipitatiou. These differences are set f )rth below, 

 together with the very satisfactory results of over five hundred similar 

 determinations made in 1882, from which it clearly appears that the 

 discrepancy formerly noticed is apparent and not real. . This conclu- 

 sion removes any doubt which hung over the practical value of the 

 optical method; and this is practically of much moment, for in the 

 rapid operations of the sugar plantation, during the pressure of the 

 crop, the polar'scope is nearly the sole dependence of the superintend- 

 ent in judging, many times daily, how his juices are running. 



The conclusions which may be drawn from our experiments are, 

 that, in experienced hands, the relative results are to be eiitirely relied 

 upon ; and, wlien the conditions which have been detailed are followed, 

 the absolute results are also satisfactory. 



Duplicate Analyses of Sorghum Juices. 

 For the purpose of controlling the results of analyses, there were 

 made, during the seasons of 1881-1882, very many analyses of sor- 

 ghum juices in duplicate. 



