The total solids in tomato pulp may be determined by drying _in vacuo_
at 70° C.; by drying at atmospheric pressure at the temperature of
boiling water; by calculation from the specific gravity of the pulp; or
from the per cent of solids, specific gravity or index of refraction of
the filtrate. The solids obtained by different methods on 31 samples of
pulp are given in Table 4.
(_a_) _By drying._—By drying either _in vacuo_ or at atmospheric
pressure, it is our experience that after the sample has reached
apparent dryness, four hours’ drying gives complete results. From 2 to
4 grams should be taken for the determination, and enough water added
to distribute the sample uniformly over the bottom of a flat-bottomed
dish at least 2.5 inches in diameter.
The solids as determined by drying _in vacuo_ at 70° C. are about 108.5
per cent of the result obtained by drying at the temperature of boiling
water at atmospheric pressure. This figure is the average of the
results obtained by the examination of 20 samples of pulp, in all of
which the per cent of solids obtained by drying _in vacuo_ agree quite
closely with the per cent obtained by drying at atmospheric pressure
multiplied by 1.085. In 15 of the 20 samples examined, the difference
did not exceed 0.10 per cent, and in only one case did it exceed 0.20
per cent. The results obtained by the subsequent examination of a
considerable number of other samples confirm this relation.
(_b_) _By calculation from the specific gravity of the pulp._—There is
a very exact relation between the specific gravity of pulp (determined
by the method given above) and the per cent of total solids as
determined by drying. The solids corresponding to pulps of various
specific gravities are given in Table 5, or may be obtained from the
following formula which is derived from the same table:
Per cent Solids = 228 (sp. gr. of pulp - 1.000) + 19.1 (sp. gr. of
pulp - 1.015).