Where the quantity used per diem is small, it is advised that precautions should be taken to preserve the quality of the chemical when a drum is opened. It might be of advantage to place the contents of the drum in smaller sealed tins, or to have made a special container (with a closely fitting lid) into which the powder can be placed as soon as the drum has been opened. MIXING SOLUTION WITH LATEX.--Emphasis has been laid, in Chapter VIII., upon the necessity for care in the preparation of the solution. Equal regard must be given to the mixture of the solution with the latex. On a few estates it used to be the practice to add the powder to the solution of acid, with stirring. Obviously this led at least to a great loss of efficiency, owing to the rapid escape of the gas which was evolved. The solution of sodium bisulphite should be poured into the latex in as uniform a distribution as possible. The mixture of solution and latex should be thoroughly stirred, and if only natives are in charge a minimum period of five minutes should be prescribed before the addition of the coagulant. A thorough stirring should again follow the advent of the acid. If these elementary rules are not observed faithfully, the deficiency will most probably be manifested in the dry rubber in the shape of streaks of varying shades of colour. Finally it may be insisted upon that deteriorated sodium bisulphite should not be used. In order to obtain an effect double the quantity may be required, and the residual salts left in the rubber on evaporation of the moisture will be responsible for prolonged drying, surface deposits, and possibly "spot disease." FORMER METHODS OF MAKING PALE RUBBER.--Merely as a matter of historic interest it may be mentioned that previous to the introduction of sodium bisulphite pale crepes were made in comparatively small quantity by various devices, among which the following might be quoted: (_a_) Use of excessive quantities of strong acetic acid. (_b_) Extreme dilution of latex in conjunction with excessive quantities of acid. (_c_) Extreme dilution in conjunction with steaming and excess of acid. (_d_) Extreme dilution of latex in conjunction with excess of acid and subsequent heating of the coagulum in hot water. (_e_) The use of excess of a mineral acid such as sulphuric acid. (_f_) The skimmings and very dilute latex, coagulated with excess of acid. WORKING THE COAGULUM.--Description of the details of necessary machinery for crepe-making is relegated to Section III. of this book. Here we shall treat only of the matter in general. In the preparation of crepe rubber heavy machinery is necessary, and ample engine-power must be available. The machines should comprise three types: (_a_) With rolls cut in such fashion, and run at such different speeds, as to have a macerating effect upon the coagulum. Such machines or rolls will be referred to as "macerators."