356 SORGHUM. 



Avholly or iu part, into cooliug or crystallizing tanks, which, being on 

 wheels, are conveniently brought under the sliding gate at the bottom 

 of the vacuum pan ; and as they are successively filled, they are 

 wheeled into a warm room, where they are allowed to remain for a few 

 hours, or even a day or two, during which time more of the sugar will 

 crystallize. 



In " striking" the pan, as the removal of its contents is termed, the 

 steam is first turned off', the vacuum is broken, the pump stopped, and 

 the contents discharged. It is, however, often the case, that but a 

 portion is removed, and that then the boiling is resumed, supplies 

 of pan sugar being drawn iu from time to time, as before. Of course 

 this results (in case no false grain is produced) in the increase in the 

 size of the crystals of sugar ; and they are often obtained, by the re- 

 peated partial striking of the pan, at last with a diameter from one- 

 sixteenth to one-eighth of an inch. But this " doubling," as the 

 operation is termed, is only possible with very pure juices, as of the 

 best sugar-cane, since the impurities of the juice are gradually accumu- 

 lating in the molasses, and finally become so abundant as to make 

 purging of the sugar difficult, if not impossible. If such " gumminess" 

 of the molasses is not excessive, a little lime-water drawn into the pan 

 during boiling, is said to remove it; but when it is such as to seriously 

 interfere with the purging of the sugar, the strike of the vacuum pan 

 should be complete, and the pan should be charged with fresh liquor, 

 as at the outset. The danger of fiilse grain being produced, is es- 

 pecially great when, after a partial strike, a fresh portion of pan- 

 liquor is drawn into the pan. 



During the entire operation, the interior of the pan may be observed 

 through the glasses in its side, and its contents examined, from time to 

 tiine, by means of the proof-stick. 



MULTIPLE EFFECTS. 



On account of the low degree of heat necessary to secure evaporation 

 in the vacuum pan, an important modification has been made by the 

 employment of what are kn<jwn as double and iripZe effects. These are, 

 in fact, a series of two or three vacuum pans, connected with each 

 other; the first being heated, as usual, and the steam from it being 

 used in the coils of the second pan, which practically plays the part 

 of a surface condenser for the first pan. In like manner, the steam 

 from the second pan passes into the coils of the third, which, in its turn, 

 acts as a surface condenser to the second pan. Finally, a condenser 

 and vacuum pump is connected with the last pan of the series, as to 

 the ordinary single vacuum pan. It is claimed that, by this arrange- 



