A quadrilateral frame on which canvas is extended for painters' uses.
In the one shown, the miter-joints have dowel-pins, and are expanded by the wedges, the pins in the open center of the latter preventing their falling out.
Commonly called gum-elastic or india-rubber.
A substance derived from the sap of various trees, of which the Jatropha elastica, called by the natives hevee, flourishing in the plains of Brazil, toward the lower part of the Amazon River, is the principal source of production.
It was first brought to Europe in the early part of the eighteenth century, and fifty years later was mentioned by Dr. Priestly as a substance excellently adapted for removing pencil-marks from paper.
Crumb of bread had previously been employed for this purpose.
The sap, obtained by tapping the trees, is dried over a fire, which gives it the dark appearance observable in the rubber of commerce.
For many years its various adaptabilities seemed