They possess a delicate Laticiferous layer of protoplasm, with numerous small nuclei lining Tissue the walls, while the interior of the tube (corresponding with the cell-vacuole) contains a fluid called latex, consisting of an emulsion of fine granules and drops of very various substances suspended in a watery medium in which various other substances (salts, sugars, rubber-producers, tannins, alkaloids and various enzymes) are dissolved.
As a secondary function we may recognize, in certain cases, the power of closing wounds, which results from the rapid coagulation of exuded latex in contact with the air.
The trees are regularly tapped and the coagulated latex which exudes is collected and worked up into rubber.
Opium is obtained from the latex of the opium poppy (Pa paver somniferum), which contains the alkaloid morphine.
In some cases (Allium, Convolvulaceae, &c.) rows of cells with latex-like contents occur, but the walls separating the individual cells do not break down.
The rows of cells from which the laticiferous vessels are formed can be distinguished in many cases in the young embryo while still in the dry seed (Scott), but the latex vessels in process of formation are more easily seen when germination has begun.
RUBBER, INDIARUBBER or Caoutchouc (a word probably derived from Cahucha or Gaucho the names in Ecuador and Peru respectively for rubber or the tree producing it), the chief constituent of the coagulated milky juice or latex furnished by a number of different trees, shrubs and vines.
The latex of the best rubber plants furnishes from 20 to 50% of rubber.
Latex, though chiefly secreted in vessels or small sacs which reside in the cortical tissue between the outer bark and the wood is also found in the leaves and sometimes in the roots or bulbs.
The latex exhibits a neutral, acid or alkaline reaction depending upon the plant from which it has been obtained.
This has been ascribed by some to the presence in " wild " rubber of certain impurities derived either from the latex or introduced during the preparation of the rubber which are thought to enhance the physical properties of the caoutchouc. It is more probable, however,.
Be feared that immature trees are often tapped and their latex mixed with that of older trees before coagulation, thus forming.
The latex of this tree flows less freely than that of Hevea brasiliensis, and the collection of large quantities of the latex is attended with considerable difficulty.
The latex is therefore usually allowed to coagulate on the tree, as it slowly exudes from the incision.
The latex, which is usually coagulated by standing or by heating, is obtained from incisions in the bark of the tree.
Besides the trees described above, a number of climbing plants or vines belonging to the Apocyanaceae secrete a latex which furnishes rubber of good quality.
The rubber is obtained by incising the stems of the vines and coagulating the latex by exposure, by admixture with acid vegetable juices or by heating.
Little is at present known of the large rubber tree of Tonkin (Bleckrodea tonkinensis), the latex of which is stated to furnish excellent rubber.
The latex is collected in the so-called dry season between June and February.
The trees are tapped in the early morning when the latex is most readily obtained.
To obtain the latex, deep incisions are made near the base of the tree extending up the trunk.
In three days, has a strong ammoniacal odour, which rapidly disappears, and in consequence of the loss of ammonia the latex will not keep for longer than a day unchanged; hence when it has to be carried to a distance from the place of collection, 3% of ammonia solution is added.
The latex usually furnished about 30% of rubber.
To obtain the rubber, the latex is usually treated in the following manner.
The seedlings rapidly developed and in most places in which they were planted grew into large trees which furnished satisfactory latex when tapped in their sixth or seventh year.
Africa the Hevea which has been planted promises well, especially in the Gold Coast, where good yields of latex are stated to have been obtained.
At present it cannot be said that finality has been reached on the subject of the best method, giving a good return of latex with a minimum of damage to the tree.
From the base - that is, within the reach of an ordinary man without the need for ladder or scaffolding; the latex obtained from the upper part of the tree is said to furnish less rubber FIG.
The latex is collected in cups placed at the apex of each V.
The yield of latex is at first small, but increases with successive tappings, which appear to stimulate the local production of latex, and finally reaches a maximum.
Too frequent tapping leads to the production of latex poor in caoutchouc, whilst tapping of trees before they are six or seven years old, and from 20-25 in.
The point of next importance is the coagulation of the latex so as to produce rubber in the form and of the quality required by the manufacturer.
As the removal of the impurities of the latex is one of the essential points to be aimed at, it was thought that the use of a centrifugal machine to separate the caoutchouc as a cream from the watery part of the latex would prove to be a satisfactory process.
This method is said to answer well with the latex of Castilloa, but it appears to be inapplicable to the latex of Hevea, which does not cream readily when centrifugalized.
The plan usually adopted is to collect the latex in rectangular tanks or casks.
After brushing away the loose stones and dirt from the root of the tree by means of a handful of twigs, the collector lays down large leaves for the latex to drop upon.
The latex, which exudes slowly and in many tortuous courses, some of it ultimately falling on the ground, is allowed to remain on the tree for several days, until it becomes dry and solid, when it is pulled off in strings, which are either rolled up into balls or put into bags in loose masses, in which form it enters commerce under the name of Ceara " scrap."
The latex coagulates readily, especially if churned or if diluted with water, when a purer rubber is obtained.
In Nicaragua the latex is collected in April, when the old leaves begin to fall and the new ones are appearing, during which time the latex is richest.
Since the latex " creams " readily the rubber can be separated from the latex by centrifugalizing, and its quality and market value thus enhanced.
The watery portion of the latex soaks into the trunk, and the soft spongy rubber which remains is kneaded and pressed into lumps or balls.
The Funtumia latex can also be coagulated by the astringent infusion of Bauhinia leaves or by exposing it in shallow dishes, when the liquid " creams."
The latex flows fairly well, but is usually allowed to dry on the tree.
The globules in the latex, however, consist more probably of a distinct liquid substance which readily changes into the solid caoutchouc. The coagulation of the latex often originates with the " curding " of the proteids present, and this alteration in the proteid leads to the solidification of the globules into caoutchouc. The latter, however, is probably a distinct effect.
Under certain conditions, as when latex is allowed to stand or is centrifugalized, a cream is obtained consisting of the liquid globules, which may be washed free from proteid without change, but, either by mechanical agitation or by the addition of acid or other chemical agent, the liquid gradually solidifies to a mass of solid caoutchouc. The phenomenon therefore resembles the change known to the chemist as polymerization, by which through molecular aggregation a liquid may pass into a solid without change in its empirical composition.
So far the chemical nature of the liquid globules of the latex is unknown, and the exact character of the change into solid caoutchouc remains to be determined.
The watery liquid known as rubber milk or latex is an emulsion consisting chiefly of a weak watery solution of proteids, carbohydrates and salts holding the liquid globules in suspension.
The dissolved salts (potassium, sodium, ammonium, calcium, magnesium, &c.) of the latex are generally nearly entirely absent from the wellprepared rubber.
There is no feasible method at present known of preventing the inclusion of the resin of the latex with the rubber during coagulation, and although the separation of the resin from the solid caoutchouc by means of solvents is possible, it is not practicable or profitable commercially.
The composition of latex and of typical rubbers is given below: