The rubber is of good quality, though, owing to the method of preparation adopted, the product is often impure and discoloured, and consequently usually brings a lower price than the best rubbers of commerce.
Pernambuco rubber, as is the case with most rubbers coagulated by saline solutions, contains a large quantity of water.
Specimens of the best known and of many of the lesser known rubbers are included in the Colonial and Indian Collections and Sample Rooms of the Imperial Institute, and many of the authentic specimens have been chemically and technically examined in the Scientific and Technical Department of the Institute and commercially valued.
Reports on many of the lesser known rubbers have been published in the Bulletin of the Imperial Institute.
The proteids should be as far as possible removed during the preparation of the rubber, as these substances are chiefly responsible for the objectionable smell and colour of " native " rubbers, and their presence leads to subsequent change in the commercial material.
The composition of latex and of typical rubbers is given below:
RUBBERS Para Ceara Castilloa Ficus Landolphia Para Latex Rubber Rubber Rubber Elastica Kirkii (Ceylon).
It is already certain that some commercial rubbers contain a variable proportion of a substance of the nature of caoutchouc, but having different properties.
True caoutchouc, the principal constituent of all rubbers, is probably essentially one and the same substance, from whatever botanical source it may have been derived.
It appears to be the principal cause of stickiness or the " tacky " condition of some rubbers, which considerably depreciates their commercial value.
Tin amalgam is used for "silvering" mirrors, gold and silver amalgam in gilding and silvering, cadmium and copper amalgam in dentistry, and an amalgam of zinc and tin for the rubbers of electrical machines; the zinc plates of electric batteries are amalgamated in order to reduce polarization.
It passes between two rubbers made of leather, and is partly covered with two silk aprons which extend over quadrants of its surface.
The glass is excited positively by friction with the rubbers, and the charge is drawn off by the action of the points which, when acted upon inductively, discharge negative electricity against it.
It was found that the machine acted better if the rubbers were covered with bisulphide of tin or with F.
The species most common are various root rubbers, notably the Carpodinus chylorrhiza.
Pierre changed places several times during the game, sitting now with his back to Natasha and now facing her, but during the whole of the six rubbers he watched her and his friend.
After six rubbers the general got up, saying that it was no use playing like that, and Pierre was released.
This viscous liquid is present in small proportion in some commercial rubbers owing to overheating during their preparation.