IMPORTANCE OF ACCURACY IN DETERMINING SPECIFIC GRAVITY
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.