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Whole pulp | Filtrate from pulp |
------------------------------+---------------------+---------+--------+
Solids by drying | | Solids by drying |Immersion| |
---------------------+ +---------------------+refract- | |
_In vacuo_| At |Specific|_In vacuo_| At | ometer |Specific|
at 70° C.| atmo- |gravity | at 70° C.| atmo- |reading | gravity|
| spheric | at | | spheric | at | at |
| pressure | 20° C. | | pressure |17.5° C. | 20° C.|
| 100° C.| | | 100° C | | |
----------+----------+--------+----------+----------+---------+--------+
_Per cent_|_Per cent_| |_Per cent_|_Per cent_| | |
13.50 | 12.44 | 1.0558 | 12.05 | 10.71 | 64.0 | 1.0523 |
13.55 | 12.49 | 1.0560 | 12.10 | 10.75 | 64.2 | 1.0525 |
13.60 | 12.54 | 1.0562 | 12.15 | 10.80 | 64.4 | 1.0527 |
13.66 | 12.59 | 1.0565 | 12.20 | 10.84 | 64.6 | 1.0529 |
13.72 | 12.64 | 1.0567 | 12.25 | 10.89 | 64.8 | 1.0531 |
| | | | | | |
13.78 | 12.70 | 1.0569 | 12.30 | 10.94 | 65.0 | 1.0533 |
13.83 | 12.75 | 1.0572 | 12.35 | 10.98 | 65.2 | 1.0535 |
13.89 | 12.80 | 1.0574 | 12.40 | 11.02 | 65.4 | 1.0537 |
13.95 | 12.85 | 1.0576 | 12.45 | 11.07 | 65.6 | 1.0539 |
14.01 | 12.90 | 1.0579 | 12.50 | 11.11 | 65.8 | 1.0541 |
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The per cent of solids in the filtered liquor obtained by drying _in_
_vacuo_, multiplied by 1.12, gives the per cent of solids in the
original pulp obtained by drying _in vacuo_. This relationship is shown
in Table 2, in the column headed “Ratio of pulp solids to filtrate
solids,” and also in Table 5.
Of the 33 samples shown in Table 2, the result obtained by multiplying
the per cent of solids in the filtrate (obtained by drying _in vacuo_)
by the factor 1.12 is very nearly identical with the per cent of solids
in the pulp (obtained by drying _in vacuo_). In 22 of the 33 samples
the difference between these two figures is less than 0.1 per cent. In
17 samples it is less than 0.06 per cent, and in 13 samples it is less
than 0.05 per cent. In only two samples does it exceed 0.17 per cent.
(_b_) _By calculation from the specific gravity of the filtrate._—The
specific gravity of the filtered liquor may be determined by means of
an ordinary pycnometer. From the specific gravity at 20° C., the per
cent of solids in the filtrate as determined by drying _in vacuo_ at
70° C. may be obtained from Table 5. It may also be calculated by the
following formula, which was derived from the same table:
Per cent Solids in Filtrate = 230 (sp. gr. of filtrate - 1.000).
The per cent of solids in the pulp may also be ascertained from the
specific gravity of the filtrate at 20° C., from Table 5. The same
results may be obtained from the following formula, which was derived
from Table 4:
Per cent Solids in Pulp =
257.5 (sp. gr. of filtrate at 20° C. - 1.000).
It is of interest to note that the table suggested by Windisch for the
determination of extract in wine (Bureau of Chemistry, U. S. Dept.
Agri., Bull. 107, revised, Table V) may be employed to determine solids
in tomato pulp from the specific gravity of the filtered liquor from
the same. If the specific gravity of the liquor be determined at 20°
C., the figures in the adjoining column, under “Extract,” correspond
very closely to the per cent of total solids in the original pulp. A
still closer agreement is obtained if the figure 0.05 be deducted from
the percentage of extract given in the table.
(_c_) _By calculation from the index of refraction of the
filtrate._—The index of refraction of the liquor obtained by filtering
tomato pulp may be determined by means of either the Zeiss-Abbé
refractometer, or the immersion refractometer at the temperature
of 17.5° C. The latter is preferable as it permits of much greater
accuracy. The corresponding percentage of solids in the filtrate and
the percentage of solids in the pulp from which it is prepared may be
ascertained from the index of refraction by Table 5. The per cent of
solids in the filtrate may also be calculated from the scale reading of
the immersion refractometer at 17.5° C. by the following formula, which
is derived from Table 5:
Per cent Solids in Filtrate =
0.258 (scale reading - 15) - 0.0165(scale reading - 26.4).
If the index of refraction has been determined by means of an Abbé
refractometer, the per cent of solids in the filtrate may be calculated
by the following formula:
Per cent Solids in Filtrate =
666(n_{D} - 1.3332) - 20.7(n_{D} - 1.3376).
The per cent of total solids in tomato pulp may also be ascertained
from the index of refraction of the liquor prepared by filtering the
pulp as shown in Table 5; or it may be calculated from the immersion
refractometer reading by the following formula, which is derived from
Table 5:
Per cent Solids in Pulp =
0.289(scale reading of filtrate - 15) - 0.0185(scale reading - 26.4).
If the index of refraction of the filtrate has been determined by
means of an Abbé refractometer, the per cent of solids in the pulp may
be calculated by the following formula:
Per cent Solids in Pulp = 748(n_{D} - 1.3332) - 25.5(n_{D} - 1.3376).
It is of interest to note that the relation between the index of
refraction of the liquor obtained by filtering tomato pulp and the per
cent of solids in that liquid is very similar to the relation between
the index of refraction and dissolved solids in beer and wine extract,
as shown in the table prepared by Wagner.[12]
[12] “Ueber quantitative Bestimmungen wässeriger Lösungen mit dem
Zeiss-schen Eintauch-refraktometer,” Table XVII.
In the formula given above, as well as in Table 5, it is assumed
that salt is absent. If it be desired to calculate the percentage of
solids in a sample containing salt from the index of refraction of
the filtrate, it is necessary first to determine the amount of salt
present and make correction therefor (see p. 34). For this purpose the
table of Wagner[13] may be employed. The correction of the immersion
refractometer reading amounts to 0.45 for each tenth per cent of salt
present.
[13] _Ibid._, Table I.
This correction is necessary if the percentage of solids be determined
by drying, or calculated from specific gravity.