96 QUANTITATIVE AGRICULTURAL ANALYMti

For liquids lighter than water:

!*«

h

and

0 ~ 130 + B
B = 1J° - 130,

where B = degrees Baum6 and S = specific gravity at 15.5° C.
Methods for Determining Specific Gravity. The Picnometer.

The most accurate method for making this determination
depends upon the use of a vessel known as a "piezometer."
There are various forms of picnometers but
the instrument is essentially a small flask
which may be weighed, first filled with water
and then with a liquid whose specific gravity

is to be measured. Specific gravity at

given by the ratio of the two weights, an ex-
plained above. Two forms of picnometers
are shown in Figs. 23 and 24.

The picnorneter flask lias an accurately
ground stopper which is borcnl longitudinally
as a capillary tube. The dry flask in first
weighed. Filled with distilled water, which
has been boiled recently to expel dissolved
air, it is then nearly immersed, in a constant
temperature bath and when the water has
been brought to the required temperature
the surplus drop is removed from the top of
the stopper. The flask in then removed
from the bath, wiped dry and weighed. It
is necessary that the room temperature shall
be a few degrees lower than that of the bath,

BO that the liquid may recede from the tip of the stopper after

removing from the bath.

After the weight of water contained at f has been determined

the flank is emptied, rinsed with redistilled alcohol and dried.

It is then filled with the liquid whose specific gravity in to be

measured and this is treated in the same way as was the water.

IG. 23.™—Picnometer
bottle, with cap.

ft ; ;. i
i n -
L .11