The description of the tables given in the following page is intended
for those operators who desire to take the trouble to obtain the
specific gravity of raw product. Where, as is often the case, the pulp
is sold under definite specifications for specific gravity, the care
necessary to make these observations with a considerable degree of
accuracy will be found to be an economy.
If a product be shipped that is materially below the specific gravity
stipulated, the manufacturer will of course be docked and the loss
will be considerable. On the other hand, the specific gravity should
not be materially above the specifications. The buyer, who is usually
a manufacturer of ketchup, desires the pulp of the specific gravity
stipulated, and a higher degree of concentration is therefore not
a mark of superiority in pulp intended for that purpose. Moreover,
material increase in concentration above the specifications of the
purchaser causes considerable loss by reason of reduced volume. For
instance, 100 gallons of pulp with a specific gravity of 1.036 are
equivalent to 103 gallons of a pulp with a specific gravity of 1.035.
Again, 100 gallons of pulp with a specific gravity of 1.040 are
equivalent to 114.7 gallons of pulp with a specific gravity of 1.035.
When these figures are considered with reference to the entire output
of the season, it is apparent that the determination of the specific
gravity of the final product is of considerable importance, and
will warrant care and, if necessary, the employment of a man who is
competent to do the work accurately.
This is well illustrated by an experience of one of the large pulp
makers, who was selling pulp under specification of 1.035 specific
gravity. Owing partly to an error in his specific gravity apparatus, he
was actually turning out pulp of a specific gravity varying from 1.040
to 1.050. In other words, each 100 cases of pulp he delivered were
equivalent to from 115 to 126 cases of pulp of 1.035 specific gravity.
While this manufacturer was using the greater part of the pulp himself,
he had contracted to sell a considerable amount of it, and all that was
supplied before the error was noticed was sold at a loss, whereas after
the error was discovered he supplied pulp well above the specifications
of the buyer at a substantial profit. Even then his profit was not what
it should have been. His output would have been 10 per cent greater
than it was if the specific gravity of his product had just complied
with his specifications.
Another manufacturer who sold his pulp under the specification of
1.035 specific gravity, received a complaint from one of the largest
buyers of pulp in the country that the specific gravity was low. The
manufacturer then examined samples, which he had retained in his
possession, of the various runs, using the method described on page 41,
under the head of “Specific gravity of cold pulp without centrifuging.”
Seventeen samples in all were examined, and he obtained an average
specific gravity of 1.0276. The purchaser had reported a specific
gravity of 1.0315–.0039 higher than that obtained by the maker. The
manufacturer then brought duplicate samples to this laboratory and the
specific gravity was determined in all of them by the method described
on page 34, “After centrifuging to eliminate air bubbles.”
While this work was being done the manufacturer himself desired to
check the mechanical centrifuge, and attempted to remove the air
bubbles from the same samples by swinging the specific gravity cups
by hand. He made a special effort to remove the air bubbles in this
way, devoting nearly a day to the examination of the 17 samples.
Notwithstanding his unusual care, his average specific gravity was
1.0318, while the centrifuge method gave 1.0328. It will be noted
that the specific gravity as determined by the centrifuge method was
.0013 higher than that obtained by the purchaser, though the latter
used a more accurate method than has ordinarily been employed in this
determination. This difference has ordinarily been regarded in the
industry as insignificant. It is apparent that it is not negligible,
however, when we consider that the difference in yield involved amounts
to over 4.5 gallons in 100 gallons of pulp.
It is true that all these results are lower than the specifications for
which this particular pulp was sold, but the incident illustrates the
importance of an accurate determination of specific gravity.