Fig. 46.—Cotton Pulp beaten 8 hours.
Some experiments were conducted by the writer in 1906 with cotton rags, in order to determine the results obtained by beating the pulp for a prolonged period under exact and specific conditions.
Fig. 47.—Cotton Pulp beaten 37 hours.
The cotton rags, of good quality, were boiled with caustic soda in the usual way for six or seven hours, at a pressure of 15 to 20 lbs., washed and partially broken down in the rag breaker, and finally bleached, made into half-stuff, and then transferred to a Hollander beating engine.
The particular conditions specified for the beating operation were that the beaterman should manipulate the pulp according to his usual routine for the manufacture of the paper which he was accustomed to make from these rags. In this case the routine process meant beating for eight hours, by which time the pulp was ready for the paper machine. In the ordinary course the pulp would be discharged into the stuff chest, and converted into a strong, thin, bank paper.
During the prolonged beating the pulp became very soft and “greasy,” and when made up into sheets the paper as it dried exhibited remarkable differences in shrinkage, the dry sheets obtained from pulp beaten thirty-seven hours being much smaller than those obtained from pulp beaten only four or six hours. The actual shrinkage is shown in the following table:—
| Hours. | Area of Sheet. Sq. mm. | Loss of Area. Sq. mm. | Relative Areas. Deckle 100 | Shrinkage per cent. |
| 0 | 26,384·0 | — | 100·0 | — |
| 4 | 26,076·0 | 308·0 | 98·9 | 1·1 |
| 6 | 25,520·1 | 863·9 | 96·7 | 3·3 |
| 8 | 25,160·0 | 1,224·0 | 95·4 | 4·6 |
| 10 | 24,794·8 | 1,589·2 | 93·9 | 6·1 |
| 13 | 24,467·4 | 1,916·6 | 92·8 | 7·2 |
| 15 | 24,215·2 | 2,168·8 | 91·8 | 8·2 |
| 17 | 24,024·0 | 2,360·0 | 90·9 | 9·1 |
| 19 | 23,616·2 | 2,767·8 | 89·6 | 10·4 |
| 21 | 23,616·0 | 2,768·0 | 89·6 | 10·4 |
| 23 | 23,535·7 | 2,848·3 | 89·3 | 10·7 |
| 25 | 23,329·9 | 3,054·1 | 88·5 | 11·5 |
| 27 | 22,920·5 | 3,463·5 | 86·9 | 13·1 |
| 29 | 22,831·2 | 3,552·8 | 86·5 | 13·5 |
| 31 | 22,492·9 | 3,891·1 | 85·3 | 14·7 |
| 33 | 21,917·2 | 4,466·8 | 83·1 | 16·9 |
| 35 | 21,226·1 | 5,157·9 | 80·5 | 19·5 |
| 37 | 20,778·8 | 5,605·2 | 78·8 | 21·2 |
If these results are plotted in the form of a curve the relation between the period of beating and the shrinkage in area is clearly shown. For the first twenty hours the shrinkage is proportional to the period of beating, after which the curve assumes an irregular shape, showing a tendency for shrinkage to proceed at a faster rate.