S22 APPENDIX. 
should be renewed, after the fermentation, by pure (or better, distilled) 
water ; then a new volume, measured, of the fermented liquid should 
be reduced to one half by evaporation, in order to abstract all the 
alcohol, and again brought to its original bulk by means of water. 
The areometrical quality of this liquid, taken after the above pre- 
cautions, will be very nearly a true indication to the amount of cor- 
rection to give to the density of the juice, provided always that it 
shows its amount of sugar. We should, at the same time, determine, 
' and separately, the correction due to the small amount of yeast 
employed. 
The process which consists in evaporating the sap to dryness ata 
temperature of 100° to 110°, in taking it back to the alcohol at 85°, 
and again evaporating (a simplification of the Péligo process) may, in 
many cases, give results with sufficient exactness for general practice. 
To know the amount of alcohol which the sap can furnish, no other 
method has succeeded better with me than the direct experiment. In 
operating upon a litre, and even a half litre, of sap, at a constant tem- 
perature of 30°, with the addition of eight to ten grammes of yeast of 
new beer to the litre of sap, I have frequently had, in eighteen or 
twenty hours, fermentations sufficiently marked to cause the density 
of the sap to fall, in this space of time, from 1-060 to 0°997. These 
figures at once show how easily the sap of the sorgho ferments, and 
how small amounts of foreign matters it contains, since, during.a 
similar experiment, the juice of the beet root never goes lower than 
1:007 or 1-008. This fermentation finished, the alcohol is determined, 
either by means of Salleron’s apparatus, or, what I consider more 
reliable, by reducing a litre or half litre of liquid. I have always 
found the results obtained hy this latter process perfectly concordant, 
and I think we nray look upon them as exact. If one has kepta 
record of the different volumes, as is done in the Salleron apparatus, 
the residuum after evaporation, are sufficient, as we have shown, to 
determine the influence which the foreign matters in the sugar exert 
upon the original density of the sap, and thus we obtain two calcu- 
lations which prove one another. 
The extraction of the sap does not present any difficulties. When 
it is proposed to determine its proportion, we may employ either of 
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