Abstract: The invention relates to a process of making articles of foamed polymethyl methacrylate (PMMA). In a first process stage a mixture comprising monomeric methyl methacrylate, plasticizer, preferably liquid foaming agent and catalyst is polymerized by heating and/or irradiation to form a foaming agent-containing solid body. In the second process stage this body is foamed by heating to the softening temperature of the plastic material. Either of these stages may also be performed continuously. The final product is clear-transparent and has large closed cells, a smooth surface, is light- and weather-resistant, readily workable, has good thermal insulation properties also in combination with plastics or glass coatings and may be used in a variety of applications, especially as a transparent insulating slab or plate.

Abstract: A solar concentrator which comprises a solid block of a transparent material having a planar incident surface positioned to receive solar rays and, opposite this surface, a curved reflective surface so that the material of the block completely fills the space between these surfaces. At the incident surface an absorber is provided and the curvature of the reflective surface is such that it is at least partly parabolical and adapted to reflect solar rays traversing the body through the body again to the absorber.

Abstract: A method of treating a porous body to increase its strength and resistance to weathering that includes first removing gases and moisture from the porous body by applying a vacuum to a vessel containing the body, then filling the vessel with an impregnating liquid consisting of a hardenable (cureable) resin and hardner so that the body is completely immersed while the vacuum is being applied, then applying a positive pressure to the impregnating liquid in which the body is immersed until the impregnating liquid has penetrated into the porous body the desired amount, then draining the impregnating liquid from the vessel while maintaining the positive pressure and then initiating the hardening of the hardenable liquid while maintaining the positive pressure, part of the impregnating liquid on the surface of the body being removed prior to hardening of the impregnating liquid in the body.