ON THE JUICE OF THE SUGAR-CANE. 301 
Guinghan canes, eighty-two parts have been extracted, and eighteen have 
escaped the action of the mill. 
It must now "be asked whether we really extract by this augmenta- 
tion of pressure a quantity of sugar " always proportioned to the q uan 
tity of juice obtained ; in other" words, if for all degrees of pressure the 
juice possesses the same qualities, and if the elements of which it is 
composed are found in the- same respective proportions. It might 
happen in the case where this proportion is broken, that the ad- 
vantage gained from. an increase of juice would be weakened by newly 
acquired properties, which interrupted the after operations, and in fact, 
rendered the extraction of sugar a more expensive and a more difficult 
operation. This is, indeed, a question which deserves to be seriously 
examined, and which has never yet been studied. It is generally 
thought that the last portions of the juice extracted from the cane, are 
similar to what flows from it at the first pressure ; and all those who 
in the various colonies Imve occupied themselves in increasing the com- 
pressive force of the sugar mills, have never doubted of its similarity. 
Some persons seemed to attribute even a richer, saccharine principle to 
the juice which flows at the last pressure. The researches I have made 
clear up this hitherto unnoticed point, and force me to adopt a totally 
different opinion. The quantity of sugar, after a certain degree of pres- 
sure, diminishes in the ratio of the augmentation of the pressure ; and 
other substances, such as the azotised principles and the mineral salts, 
proceed in an inverse ratio, increasing with the pressure. This result is 
one of the most manifest, and is explained by the differences of weight 
which one is far from expecting. 
But what are the causes of such modifications ? You will seek it 
in vain except in the constitution of the plant itself and the unequal re- 
sistance of its various parts. The medullary portions being really 
supplied with a juice more saccharine, offering less obstacle to the ac- 
tion of the press or cylinders, allow the juice to flow more freely, whilst 
the bark and the concentric tissues, less rich in sugar, have far more 
resisting power, and thus much longer retain the juices with which they 
are impregnated. 
Here are some results which strengthen this argument and which 
give the measure of the differences observed under these circumstances, 
whatever portion of the canes be examined, whether the knots of the 
cane, or the intervening parts be crushed or not. A certain quantity of 
cane has at first been subjected to a pressure equal to that obtained 
from a mill which yields 60 per cent, and then to a second pressure of 
a mill capable of yielding 78 per cent. 
The juice obtained in the first instance was clear and limpid ; in the 
second, its clearness was thickened because it contained a greater quan- 
tity of organic remains. After being filtered with care, an analysis was 
made under exactly similar conditions. 
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