EXTRACTION OF SUGAR FROM BEETS. 333 



charcoal is added ; after which ebullition is renewed till the 

 sirup rises to 28°, (=: 1.242,) when it is filtered and dried. 

 I have found this to be the only way in which I 

 could restore a sirup which had been injured in the 

 process. 



I have myself made particular observations upon the 

 thick, whitish, unctuous and paste-like substance, which 

 is almost always found upon the sirup, and which, when it 

 is abundant, prevents the drying from being well-termi- 

 nated. This substance renders the sirup ropy, adheres to 

 the sides of the boiler, which are blackened by it, separates 

 itself from the sirup, in proportion to its concentration, and 

 prevents the object proposed from being attained. 



I have noticed that the quantity of this substance was in 

 proportion to the germination of the roots, and that it was 

 increased by the incomplete purification of the sirup, and 

 also by a slow evaporation. Animal charcoal produces an 

 astonishing effect in lessening the quantity of it ; sometimes, 

 if well employed, the formation of it is prevented, or that 

 which is produced is made to disappear. 



This substance, which, during the first years of my es- 

 tablishment, I often collected in large quantities, is thick- 

 ened and hardened by cold; it is insoluble in water or 

 alcohol ; it burns with a white and inodorous flame ; and 

 possesses all the characteristics of vegetable wax, from 

 which it is in no wise different. 



The drying is ended when the boiling sirup marks 44° 

 or 45°, (= specific gravity of 1.440 to 1.454.) The time 

 for removing the sirup from the boiler may be known by the 

 following signs. 



1. Plunge a skimmer into the boiling sirup, and upon 

 withdrawing it pass the thumb of the right hand over its 

 surface ; mould the sirup which adheres to the thumb be- 

 tween that and the fore finger, till the temperature be the 

 same as that of the skin ; then separate the thumb and 

 finger suddenly ; if the boiling be not completed, no thread 

 will be formed between the two ; if there be a filament, the 

 boiling is well advanced ; and the process is completed as 

 soon as the filament breaks short, and the upper part, hav- 

 ing the semi-transparency of horn, curls itself into a spiral. 

 This manner of trying the sirup is known by the name 

 proving. 



2. The second mode of judging of the completion of 

 the process, is by observing the time when the sirup ceases 



