=26. Drying Viscous Liquids.=—In the case of cane juices, milk,
and similar substances, the paper coil method may be used.[11] The
manipulation is conducted as follows: A strip of filtering paper from
five to eight centimeters wide and forty centimeters in length, is
rolled into a loose coil and dried at the temperature of boiling water
for two hours, placed in a dry glass-stoppered weighing tube, cooled
in a desiccator and weighed. The stoppered weighing tube prevents the
absorption of hygroscopic moisture. About three cubic centimeters of
the viscous or semi-viscous liquid are placed in a flat dish covered
by a plate of thin glass and weighed. The coil is then placed on end
in the dish, and the greater part of the liquid is at once absorbed.
The proportions between the coil and the amount of liquid should be
such that the coil will not be saturated more than two-thirds of its
length. It is then removed and placed dry end down in a steam-bath
and dried two hours. The dish, covered by the same plate of glass,
is again weighed, the loss in weight representing the quantity of
liquid absorbed by the coil. After drying for the time specified the
coil is again placed in the hot weighing tube, cooled and its weight
ascertained. The increase represents the solid matter in the sample
taken. This method has been somewhat modified by Josse, who directs
that it be conducted as follows:[12] Filter-paper is cut into strips
from one to two centimeters wide and three meters long. The strips are
crimped so they will not lie too closely together and then wrapped
into coils. These coils can absorb about ten cubic centimeters of
liquid. One of them is placed in a flat dish about two centimeters
high and seven in diameter, and dried as described, covered, cooled
and weighed. There are next placed in the dish and weighed one or two
grams of the massecuite, molasses, etc., which are to be dried and the
dish again weighed and the total weight of the matter added, determined
by deducting the weight of the dish and cover. About eight cubic
centimeters of water are added, the material dissolved with gentle
warming, the coil placed in the dish, and the whole dried for two
hours. The cover is then replaced and the whole cooled in a desiccator
and weighed. The increase in weight represents the dry matter in the
sample taken.
The above method of solution of a viscous sample in order to divide
it evenly for desiccation is based on the principle of the method
first proposed by the author and Broadbent for drying honeys and other
viscous liquids.[13] In this process the sample of honey, molasses, or
other viscous liquid is weighed in a flat dish, dissolved in eighty
per cent alcohol, and then a weighed quantity of pure dry sand added,
sufficient to fill the dish three-quarters full. The alcoholic solution
of the viscous liquid is evenly distributed throughout the mass of sand
by capillary attraction, and thus easily and rapidly dried when placed
on the bath.
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