October i, 1903.] 



THE INDIA RUBBER WORLD 



has not intended any attack upon any individual who may have 

 been connected with the business. But the incident should 

 serve as a warning to honest men generally to be more careful 

 about lending their names to the promotion of stock selling 

 schemes. 



SOME CONCLUSIONS REGARDING RUBBER CUL- 

 TURE. 



BY ORATOR F. COOK.* 



THE culture of the Central American rubber tree has 

 passed the experimental stage in the sense that the prac- 

 ticability of the agricultural production of rubber has been 

 demonstrated, but on the other hand it has been ascertained 

 that the tree may thrive where it will yield little or no rubber. 

 Under favorable natural conditions the culture of Caslilja 

 elastica bids fair to become very profitable, but the experi- 

 mental determination of the factors which influence the pro- 

 duction of rubber has scarcely begun. [The spelling Costilla, 

 instead of Castilloa, has been adopted at Washington, on ac- 

 count of its being the original form.] 



In southern Mexico and Central America the regions well 

 adapted to the culture of Castilla are much more limited than 

 has been supposed. The presence of wild Castilla trees is not 

 a sufficient evidence that a locality is suited to commercial 

 rubber culture. 



Differences in the yield of rubber are not due merely to the 

 existence of different species and varieties of Castilla, but are 

 also controlled by external conditions. 



The functions of the rubber milk in the economy of the plant 

 are not well understood or agreed upon by botanists, but there 

 are numerous reasons for holding that in Castilla and many 

 other plants it aids in resisting drought. 



A continuously humid climate is not necessary to the growth 

 and productiveness of Castilla ; the indications are rather that 

 the quantity of milk and the percentage of rubber are both in- 

 creased by an alternation of wet and dry seasons. 



In its wild state Castilla does not flourish in the denser for- 

 ests, but requires more open situations. It is confined to forest 

 regions only by the perishability of its seeds. 



Castilla thrives better when planted in the open than in the 

 dense forests ; even young seedlings are not injured by full ex- 

 posure to the sun, providing that the ground does not become 

 too dry. 



The planting of Castilla under shade or in partially cleared 

 forests is to be advised only on account of special conditions or 

 as a means of saving labor and expense. 



The loss of the leaves in the dry season may be explained as 

 a protection against drought, and does not indicate conditions 

 unfavorable to the tree or to the production of rubber. 



The falling of the leaves of Castilla elastica in the dry season 

 renders it unsuitable as a shade tree for coffee or cacao. In 

 continuously humid localities where the leaves are retained 

 shade trees are superfluous and the yield of rubber declines. 



The desirable features of shade culture, the shading of the 

 soil, and the encouragement of tall upright trunks, are to be se- 

 cured by planting the rubber trees closer together rather than 

 by the use of special shade trees. Planting closer than 10 feet, 

 however, is of very doubtful expediency. 



The percentage of rubber increases during the dry season 

 and diminishes during the wet. The flow of milk is lessened in 

 dry situations by inadequate water supply, but at the beginning 



of the rains such trees yield milk much more freely than those 

 of continuously humid localities. The claim that more rubber 

 is produced in the forest or by shaded trees seems to rest on 

 tapping experiments made in the dry season. 



Continuous humidity being unnecessary, the culture of Cas- 

 tilla may be undertaken in more salubrious regions than those 

 to which rubber production has been thought to be confined ; 

 the experimental planting of Castilla in Porto Rico and the 

 Philippines becomes advisable, but extensive planting in untried 

 conditions is hazardous. 



No satisfactory implement for the lapping of Castilla trees 

 has come into use. Boring and suction devices are excluded by 

 the fact that the milk is contained in fine vertical tubes in the 

 bark, which must be cut to permit the milk to escape. 



In British India it has been ascertained that the Pari rubber 

 tree may be repeatedly tapped on several successive or alter- 

 nate days by renewing the wounds at the edges. The yield of 

 milk increases for several tappings and the total is unexpect- 

 edly large. It is not yet known whether multiple tapping is 

 practicable with Castilla, or whether this new plan may not 

 give the Para rubber tree a distinct cultural advantage over 

 Castilla. 



The gathering of rubber from trees less than eight years old 

 is not likely to be advantageous; the expense of collecting will 

 be relatively large, and the quality of such rubber is inferior, 

 owing to the large percentage of resin. 



The rubber of Castilla is scarcely inferior to that of Hevea. 

 The supposed inferiority is due to substances which can be 

 removed from the milk by heat and by dilution with water. 



THE ECONOMY OF RUBBER COLORS. 



♦These paragraphs form the concluding chapter of a late publication by the 

 United States department of agricuhure, of whch a review appears on another 

 page of this Journal. — The Editor. 



EVERY one familiar with the use of dry pigments in rub- 

 ber compounding has noted the remarkable differences, 

 at any given price per pound, in the coloring effect obtainable 

 from colors of the same designation. The variations in this 

 regard are often so great that a serious question of economy is 

 involved in making a selection. 



Most of the dry colors used in rubber work are not chemi- 

 cally inert, like the ordinary fillers, barytes, silica, whiting, and 

 asbestine, and therefore should not be used beyond the amounts 

 necessary to produce the desired color. The strongest pig- 

 ment — that is, the one capable of yielding the greatest coloring 

 effect, at a given price per pound — is invariably the one to use. 

 The various grades of color of the same maker are graded in 

 coloring quality to correspond with the prices asked, but be- 

 tween two makers of ostensibly the same goods there is not in- 

 frequently a variation in coloring value of several hundred per 

 cent., when compared by " money equivalent weight." By this 

 term is meant the amount of each color purchasable for a given 

 sum. 



The strength of a pigment, or its ability to impart its color 

 when mixed in a rubber compound, depends principally on its 

 degree of fineness. Each particle of pigment, however finely 

 divided, has the same color quality as every other particle in 

 the same pigment, and consequently the greater number of par- 

 ticles in a given bulk the larger the amount of material to 

 which the pigment can impart its color. In other words, the 

 more finely ground the pigment, the more adulteration or dilu- 

 tion it can stand. Every color should thus be reduced to im- 

 palpable fineness. Whetherthis has been done or not with any 

 sample is easily determined by rubbing a pinch of the material 

 between the thumb nails. The slightest amount of grit can 

 quickly be detected in this manner. 



The "relative economy of two pigments is simply ascertained 



