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When fluxing is complete, the weight of soap above indicated is added slowly, rate of adding depending upon the amount of foaming which takes place, which is, of course, dependent upon the water content of soap. Soap should be distributed over the surface of the asphalt as much as possible to aid in the speed of mixing. Mechanical propellers or hand operated wooden paddles are used for mixing. When the soap is all dissolved, the mass will appear homogeneous and the surface of the asphalt will be almost free from foam. Appearance of lumps on the paddle will indicate the necessity for further stirring. During this operation the temperature should drop to about 120° C., and should be maintained at that point. The complete dissolving of the soap is one of the most important steps in the process.
When this has been effected, transfer 683 (sixty-eight and three-quarters) Imperial gallons of this hot asphalt-soap mixture to the mixing tank, care being taken to stir thoroughly the contents of the kettle before each batch is drawn. The mixer tank should be warmed by means of a kerosene burner or other convenient method. The blades of the mixer should be revolving while the asphalt is being poured in. Then start adding water very slowly and carefully at first, to prevent excessive foaming. When further additions of water show no signs of dangerous foaming the water can be added faster. The entire amount of water, 561 (fifty-six and one-quarter) Imperial gallons can be added in between five and six minutes, the temperature of the asphalt- -soap mixture being kept at the prescribed temperature of 120° C.
Mixing should be continued for about two minutes or until the mass appears homogeneous and the emulsion is of a dark brown colour. When the process is complete a mixture of about 1 cubic centimetre with about 50 c.c. of water should show complete miscibility with no signs of separate asphalt particles. The temperature of the finished emulsion should be about 80° to 85° C. At a temperature of 15'5° C. it should have a specific gravity of approximately 1095.
The type of soap to be used should be stated when indenting for the other materials. Almost any type of laundry soap would be found suitable but the preparation may need to be changed to suit. The water content of ordinary bar soap is a variable and this will be a factor which will require consideration. Soap chips, flakes or pulverized soap show the least water content and therefore require less and will dissolve more readily. As experience is gained the quantity of soap actually required may be found to be less than that prescribed above.
Some oversea territories (e.g. Tanganyika) have local soap making works. In order to judge of the suitability of the locally made soap for emulsion making, it would be advisable if a sample of 25 to 50 lb. could be sent home for test as an emulsifying agent. When the matter was discussed recently with an East African merchant, and the fact was pointed out that Indian natives use what is known as the Rita berry in place of soap, and that this led to its use as an emulsifying agent, the merchant in question cited a similar case in which the outer fleshy covering of the coffee bean was used by the African natives for cleansing purposes. If it were possible to store this bye- -product of the coffee growing industry for a month or two, its properties as an emulsifying agent might prove worth investigation. In this case also the Trinidad Lake Asphalt Company would be prepared to conduct experiments on receiving a sample of about 50 lb.
Extremely hard water should be avoided if possible since such water will require additional soap. The amount of water may be increased materially, but a consequent reduction in the amount of asphalt will result. The water content may be decreased as desired, but the fluidity of the finished product required will govern this.
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