STANDARD SHEET.--Leaving for the present the question of pattern of mark, one cannot do better by way of introduction than to reproduce the instructions[8] given generally to estates. [8] "Handbook on Preparation of Rubber," Rubber Growers' Association, May, 1917, p. 28. ROLLING AND MARKING OF SHEET RUBBER.--Working with standard latex it is found that strips of coagulum 1-1/2 inches in thickness require little rolling to produce sheets of desirable thickness. (1) The sheets or strips are first given a preliminary rolling with a heavy hand-roller made of hard wood. The roller is passed once in one direction, and once in the reverse direction. (2) The coagulum is then passed through smooth machines twice, once with the rolls fairly open, and once with a narrower space. It is not found advisable to close the smooth rolls so tightly that the rubber is made too hard. (3) The sheets or strips are then passed once through a pair of marking rollers. Various types of patterns are used, but the one which appears to give the most satisfactory results is that known as the "close-cut spiral." This produces the semblance of a small diamond pattern on the rubber. The surface of the sheet is raised in well-defined ridges, which appear to present the maximum drying surface exposed to the atmosphere of the smoke-house. Thus, not only is the appearance of the sheet rendered attractive, but also the period of drying is reduced. Starting with standard latex and following the procedure here described for rolling and marking, sheets should be ready for packing in ten or eleven days. If the period is longer, it is possible that the design or structure of the smoke-house is at fault. WHEN TO WORK THE COAGULUM.--Before proceeding to discuss other points the question remains to be settled as to how long it may be necessary or advisable to allow the coagulum to remain in the serum before rolling it. For reasons of practical economy in factory working, it is usual to allow sheet rubber to remain over night, and the coagulum receives attention early next morning. During the interval (averaging about eighteen hours), the coagulum consolidates, leaving an almost clear serum if the correct quantity of acid has been added to the latex. Any but the very slightest trace of milkiness in the serum indicates an insufficiency of coagulant. If the serum is always definitely clear, there may be grounds for believing that an excess is being used. If the quantity of coagulant has been calculated to an average nicety, the serum should be just dubiously free from milkiness. The firmness gained by the coagulum on standing in the serum overnight should enable it to be handled next morning without any marked stretching, and in some estates the rubber is put direct through the first pair of smooth rolls without a preliminary consolidation by means of hand-rolling.