----------+--------------+--------------+------------+--------------- | Weight of | Thickness of | Grams per | Lbs. per ream Hours. |20,000 sq. mm.| Sheet. | sq. metre. | 480 sheets, | Grams. | mm. | | 20" × 30". ----------+--------------+--------------+------------+--------------- Class A | | | | 8-10 hrs. | 1·875 | ·183 | 93·75 | 38·23 | | | | Class B | | | | 19-21 hrs.| 2·043 | ·189 | 102·15 | 41·65 | | | | Class C | | | | 33-35 hrs.| 2·203 | ·189 | 110·15 | 44·93 ----------+--------------+--------------+------------+-------------- _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. ----------+-----------------------------------+--------- | Percentage of Size absorbed. | Hours. +-----------+-----------+-----------+ Mean. | 1st Trial.| 2nd Trial.| 3rd Trial.| ----------+-----------+-----------+-----------+--------- 8 | 5·5 | 6·0 | 6·2 | 5·9 10 | 5·4 | 6·8 | 6·5 | 6·2 19 | 3·8 | 5·0 | 4·5 | 4·4 21 | 4·8 | 3·9 | 4·6 | 4·4 33 | 2·7 | 1·7 | 2·4 | 2·3 35 | 2·4 | 1·9 | 1·7 | 2·0 ----------+-----------+-----------+-----------+--------- 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.