Since this apparatus is likely to be broken, it is well for each plant
that contemplates using the method to equip itself with at least two of
each item mentioned above.
The Brix hydrometer mentioned above is suggested because it is a stock
article handled by all dealers in chemical apparatus and can be secured
quickly. It has the disadvantage that it is relatively large, and in
order to use it the filtrate must be prepared in much larger quantity
than would be required by a smaller hydrometer. By placing orders well
in advance with dealers in chemical apparatus special hydrometers may
be made with a bulb about one-half inch in diameter and with a total
length of five or six inches. Such hydrometers could be used with a
cylinder as small as one inch in diameter. They would require much less
liquor than is necessary for the Brix hydrometer and therefore would
enable the analyst to obtain results much more quickly. In securing
such hydrometers it would be well to order several at a time, since it
would require several weeks to replace any that may be broken.
The details of the method are as follows:
Place a piece of cotton cloth of about the texture of ordinary glass
toweling over a clean, dry container 10 or 12 inches in diameter or
over a No. 10 can. Pour on the cloth a suitable amount of the pulp
or cyclone juice to be examined, pick the cloth up by the corners
and squeeze gently to separate the greater part of the insoluble
solids. The strained liquid left in the vessel will be more or less
turbid, according to the pressure exerted in squeezing. The amount of
insoluble material producing this turbidity, however, is not usually
sufficient to interfere with the examination of the product by means
of a hydrometer. If, however, it is necessary to exert considerable
pressure to get the amount of filtrate desired and the turbidity is
therefore considerable it will be necessary to pass the liquor through
a second filter, which, of course, may be done quickly.
Transfer this strained liquid, which for the sake of convenience we
will designate as “filtrate,” to the 2-inch cylinder described above,
and lower the Brix hydrometer into it until the hydrometer floats.
When the hydrometer, becomes stationary, the reading on the stem is
taken. In reading the hydrometer it will be noted that, owing to
the meniscus, the liquid immediately at the stem rises one or two
divisions above the general surface. The reading at the lowest point
of the surface is desired. In reading the stem, therefore, allowance
for the meniscus should be made and a reading recorded one or two
divisions on the scale below the extreme height of the meniscus on
the stem. The reading so obtained is recorded as the Brix hydrometer
reading of the filtrate.
After determining the Brix reading of the filtrate from the tomato
pulp, the corresponding specific gravity of the pulp may be obtained
from Table 9. The result obtained by the method should be corrected to
the temperature of 68° F., according to Table 8. If it is desired to
use the reading of the filtrate from cyclone juice for the purpose of
controlling the evaporation of tomato pulp, suitable directions are
given below under “Evaporation to Specific Gravity Desired.”