346 ON THE JUICE OF THE SUGAR-CANE. 
becomes indispensable to fulfil certain conditions, which fortunately are 
easily realised. The first is, to work always at the same temperature, 
namely, 25° centigrade, to which degree of heat the juice can easily 
be brought ; for the average temperature of the first months of the sugar 
crop is 23° centigrade in the shade, and that of the last month, 27° 
The second is, the use of a correct instrument, however its scale 
may be graduated. The areometers of Braume" in ordinary use have on 
a very short stem relatively too many principal divisions to be accu_ 
rately used in the juice, the extreme limits of which are for the canes 
usually employed, 8° and 12°. But in order to remedy this in- 
convenience, and at the same time to give such experiments more pre- 
cision, I have arranged an areometer with a long and perfectly cylindri- 
cal stem, on which is marked only the degrees of 6 and 13, each of these 
principal divisions being divided into tenths. With this instrument 
the density of the juice can be registered to one-tenth of a degree. But 
in order that the indications of the areometer may be really useful to the 
planter, it is requisite that such an instrument should show him ap- 
proximately the proportion of sugar contained in the juice the density 
of which he has ascertained. 
For this purpose different methods have been proposed. Being based 
on the proportion of sugar which a certain weight of distilled water con- 
tains at a given temperature, they are defective, because a solution of 
crystallizable sugar, varying only in the quantity of saccharine matter it 
contains, cannot be compared to the juice into which there sometimes 
enter notable quantities of other substances besides crystallizable sugar, 
these substances themselves undergoing great changes according to the 
different areometric degrees. Experience alone — that is, on the one hand 
the determination of the density of a great number of juices, and, on the 
other hand, the comparative chemical analysis of these same liquids 
— could conduce to the formation of a table presenting any exactness. 
Taking as a basis all the analyses of the cane-juice which I have 
made during a period of nearly two years, amounting to a hundred at 
least, I have framed the following table, fn which opposite to the degree 
of the areometer will be found the quantities of crystallizable sugar for 
one litre of juice and 1,000 grammes of this liquid; that is, the corre- 
sponding quantity of sugar for the juice, regarded in volume or weight* 
In the fourth column of this table are recorded the considerable dif- 
ferences produced by the presence in the juice of other substances than 
sugar. To insist further on the modifications which these substances 
produce in the juice would be simply to anticipate what I shall have to 
say with regard to these substances themselves. It is, therefore, suffi- 
cient for me to point out the part to be assigned to them in the deter- 
mination of the density of the cane-juice. 
