RUBBER 



RUBBER 



557 



Preparing. — Rubber may be made in various 

 forms, the best of which are biscuit, crepe or sheet, 

 and block. For biscuit, the latex, after being strained 

 through muslin or wire gauze to remove any dirt, 

 is poured into enameled iron plates. A few drops of 

 acetic acid are put in each plate, and the milk 

 stirred. The plates are covered and put aside for 

 about twelve hours, when the latex is found to be 

 set, and can be taken out in a cake. It is then put 

 between rollers and rolled flat, and laid away on a 

 rack to dry, in a cool, dry place. The drying usually 

 takes some weeks. When quite dry the biscuits are 

 packed in wooden boxes for shipment. If in drying 

 mold appears, the biscuits are wiped with a rag 

 moistened with formalin. 



Some planters do not use acetic acid, but allow 

 the latex to coagulate of itself. The objection is 

 that it takes a much longer time to set, and the 

 latex is liable to suffer from the decomposition 

 bf the proteids. Rubber is also sometimes smoked 

 over a wood fire. This accelerates the drying but 

 darkens it and sometimes causes a small reduction 

 in value. 



Sheet rubber is made in the same way but in 

 long, fiat trays. CrSpe is made in a machine in- 

 vented in the Malay states, the rollers of which 

 are grooved and tear up and press the soft rubber 

 together again, making it of a lace-like appearance. 



There is a slight preference at present for bis- 

 cuit and sheet rubber over crepe, but the latter 

 has the advantage of drying more rapidly. Block 

 rubber has recently come into prominence. 



Scrap is the waste bits of rubber derived from 

 the cuts when reopening, and any other bits which 

 cannot be made into biscuits. The washings of the 

 cups and splashes of milk, and in fact every drop 

 of latex, collected into a v,'ooden tub and coagu- 

 lated with acid, go into the rcrap. 



Returns and profits. — Every well-grown tree of 

 six years (in the Straits Settlements) should give 

 three-fourths to one pound of dry rubber per year, 

 and increase as the tree grows. The price of plan- 

 tation rubber has been extraordinarily high of 

 late, reaching as much as seven shillings a pound. 

 Although it is difficult to forecast even an average 

 price of the product, at a reduction of one-half of 

 the present value the planter would still gain a large 

 profit. It is estimated in the East that the cost of 

 making the rubber and putting it on the market is 

 five to ten cents Mexican, or one to two pence per 

 pound ; in Trinidad it is eight pence to one shilling. 

 The scrap, if tolerably clean, is worth one or two 

 shillings less per pound, but usually brings a 

 higher price than the best African rubber. 



Central American or Panama rubber (Castilba 

 elastica). Fig. 794 ; Fig. 120, Vol. I. 

 The Central American rubber, a tree allied to 

 the bread-fruit, is a native of the northern parts 

 of South America and Central America, and is 

 more suited for cultivation in latitudes ten degrees 

 north of the equator. It does not seem ever to have 

 been grown successfully along the equator. The 

 area of its successful cultivation lies north of the 

 region for the latter plant. Cultivated trees reach 



a height of sixty feet, with a diameter of eighteen 

 inches, in twenty years. 



The plant is raised from seed in nursery-beds, 

 and when about a foot tall is removed to the plan- 

 tation. It thrives best when planted not too thickly 

 with other trees. The tree can be tapped in the 

 same way as Para rubber at about eight years of 

 age. A spiral form of cut is often used (see 

 Vol. I, page 108), but is not recommended. With 

 this tree, as with all others, it is best not to tap too 

 early, as such treatment is likely to affect later 

 production. A better quality of rubber is pro- 

 duced as age advances. The latex is coagulated by 

 adding boiling water to it, and, after straining, 

 by adding eight ounces of formaldehyde to a barrel- 

 ful. Then the creamy mass is washed again and 

 rolled out, or it may be mixed with water in a bar- 

 rel with a tap at 



the bottom. This /]\ 



water is drawn 

 off in about 

 twelve hours, 

 and the opera- 

 t i n repeated 

 two or three 

 times, when the 

 cream is allowed 

 to coagulate and 

 is then rolled 

 out. 



Separation 

 can also be ef- 

 fected by cen- 

 trifugal action, 

 but the frequent 

 stoppages neces- 

 sary are an ex- 

 pensive waste of 

 time. By this 

 process the rub- 

 ber is rapidly 

 brought to the 

 surface of the 

 vessels used, and 

 requires only to 

 be dried. A con- 

 venient method 

 of coagulating 

 and drying is by 

 means of the 

 "sand filter," 

 which can be used in connection with either the 

 creaming or the centrifugal process. A centripetal 

 method is now under trial, which is inexpensive 

 and is expected to work with great economy. If 

 the latex is left in the original fluids after strain- 

 ing through a fine mesh, it quickly ferments and 

 becomes putrid; the rubber will then coagulate 

 and float on the surface, and there is but trifling 

 loss. The rubber thus produced is dark in color, 

 but of good quality, free from resinous matter and 

 keeps well. The method, however, is tedious, repul- 

 sive, and takes considerable time. (Hart.) 



The amount of rubber from a tree is variously 

 stated. An eight-year-old tree probably gives about 



Fig. 704. PistiUate (left) and stami- 

 nate (right) flowers and leaf of Cas- 

 tilloa. (Adapted from Bulletin No. 

 49, Bureau of Plant Industry.) 



