98

QUANTITATIVE AGRICULTURAL

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which apply to special industrial uses.   Two
of these will be mentioned.
Lactometer. — This is an instrument much
used in dairy laboratories. Quovenne's
lactometer is graduated in degrees from 15
to 4.0, corresponding to specific gravity
1.015 to 1.040. The New York Board of
Health lactometer also is graduated in
arbitrary degrees in such manner that 0°
corresponds to specific gravity 1.000 and
100° to 1.029, the latter figure being con-
sidered as the average specific, gravity of
pure milk. Degrees on this lactometer
would thus roughly indicate the per cent of
whole milk in a milk and water mixture.
Other special names, such as "saceharo-
meter," "alcoholometer," etc., apply to
hydrometers for sugar solutions, alcohol
and other special uses.
In using hydrometers the temperature at
which the experiment is performed must be
that for which the instrument is calibrated
and care must be taken to remove* air bub-
bles which might cling to the hydrometer
and thus increase the effective displace-
ment.
The floating hydrometer in much used
for measurements not requiring great, ac-
curacy, as a reading is very quickly made.
The scales found on the stems are fre-
quently very inaccurate and any hydrom-
eter should be calibrated by the use of
liquids of known specific gravity.
Westphal Balance.— In effect, this
balance (Fig. 26) weighs the liquid which
f^ _ ^>Sx^-> is displaced by an immersed plummet
fig. 25. — Pleating hy- whose displacement of water is known.
drometer and cylinder,   mi.      t~   i	/*    i   \	i ^   «   ^         i •     a
I he balance is first brought into adjust-
ment with the dry plummet hanging on the beam.    A cylin-