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THE POPULAR SCIENCE MONTHLY 



the drying out of the shrub and breaking off of twigs. Since it was 

 found possible to increase the field weight by methods devious and of 

 little cost, thus selling stones or water at an exceptional price even in a 

 country where that commodity is not cheap, a control by means of tags 

 was devised, enabling a systematic comparison of the field and factory 

 weights of shrub from all areas. The price of water quickly fell. 



Manufacture 



To keep a large plant running regularly a considerable reserve of 

 shrub must be held. This was formerly stacked in the open, but later, 

 when rapid deterioration was discovered, suitable storage warehouses 

 were provided, thus obviating the deleterious action of the sun. When 



Fig. 11. Packing Guayui.e Rubber at Torreon, Coahuilla. 



the shrub is in good condition — that is, sufficiently, but not too dry — 

 the bales are passed out to a washing floor where all dust and soil is 

 removed by a stream of water. The importance of this becomes ap- 

 parent when it is reflected that the rubber picks up particles of soil and 

 its specific gravity altered, so making the separation of rubber and 

 bagasse more difficult. 



The shrub is now run between the steel rolls of a crusher which, 

 running at differential speeds, grind up the plants into torn fragments. 

 Peons take this material up in baskets and convey it to pebble mills. 

 These are short iron cylinders which are arranged so as to rotate on 

 their axes. Each mill is lined with flint bricks and is charged with 

 ground shrub, water and coarse flint pebbles which by their impact on 

 each other comminute the shrub and agglomerate the rubber. After 



