Weight and Substance of the Paper.—The shrinkage of the paper after prolonged beating indicates a closer and denser sheet, so that for papers of equal thickness the weight per unit area was much greater in the case of the pulp beaten for the full period. The results obtained are very interesting, and the following summary for a few of the readings obtained will serve to show the alteration effected.

Hours.Weight of
20,000 sq. mm.
Grams.		Thickness of
Sheet.
mm.		Grams per
sq. metre.		Lbs. per ream
480 sheets,
20" × 30".
Class A
8-10 hrs.		1·875·18393·7538·23
Class B
19-21 hrs.		2·043·189102·1541·65
Class C
33-35 hrs.		2·203·189110·1544·93

Sizing and Glazing Effects.—The behaviour of the waterleaf paper after sizing and glazing gave some interesting results. In the first place, the effect of the altered density of the paper is strikingly shown by the amount of the size absorbed. Certain selected sheets were passed through a solution of ordinary gelatine in the usual way, and subsequently dried. The amount of gelatine absorbed differs in a remarkable degree, as shown in table.

Tensile Strength of the Paper.—It is interesting to note that the tensile strength of the waterleaf papers appears to remain fairly constant throughout the whole period of beating. But this uniformity is greatly altered by the operations of sizing and glazing.

Percentage of Air-dry Gelatine absorbed by the Waterleaf Sheets.

Hours. Percentage of Size absorbed. Mean.
1st Trial. 2nd Trial. 3rd Trial.
85·56·06·25·9
105·46·86·56·2
193·85·04·54·4
214·83·94·64·4
332·71·72·42·3
352·41·91·72·0

These results are rather remarkable. The prolonged beating does not seem to have affected the tensile strength of the waterleaf, and the practical loss of strength which actually occurs in the more completely finished paper does not manifest itself until after the sizing process. The importance of the gelatine as a factor in the ultimate strength is thus clearly and strikingly demonstrated.

Tests for Strength on Original Waterleaf Paper.