Abstract: Process for pretreatment at atmospheric pressure or a pressure close to atmospheric pressure by alkaline wetting and holding at temperature of natural materials whose gangue comprises argillaceous compounds capable of forming a stable plastic suspension in the presence of water and containing at least one combustible element which can be put into useful form wherein, in order to permit subsequent easy operations for separation of the liquid aqueous and solid phases of the gangue:(a) the natural material which was possibly been subjected to a preliminary drying operation is brought into intimate contact with at least 4 kg expressed in terms of OH.sup.- of at least one alkaline agent per ton of clay contained in said material, the total volume of liquid present in the natural material after the contacting operation being such that the ratio L/S of said volume expressed in terms of cubic meters to the weight of solid expressed in tons of dry ore is at most equal to 0.

Abstract: An optical system for analyzing and correcting wave fronts comprising a deformable mirror for correcting wave fronts and a system for analyzing and detecting phase distortion, an interferometer with lateral duplication constituting the analysis system, receiving the wave front for analysis and duplicating it and deducing from two neighboring wave fronts obtained signals to control deformation of the deformable mirror, wherein this lateral duplication interferometer is a polarization interferometer consisting of a Wollaston double-refractive biprism with an angle .theta., the two prisms being assembled head to tail and cut parallel to the crystallographic axis such that the respective axes are parallel and perpendicular to the edges of the prisms, a polarizer and an analyzer on either side of the biprism and an oscillating optical member on the path of the biprism.

Abstract: A method for measuring the bonding power of an adhesive material, particuly a sheet material comprising fibres impregnated with a glue. After having applied against the material the face of a totally reflecting prism the index of refraction of which is lower than that of the glue, a force is exerted which tends to bring apart from each other the prism and said material, the value of the force corresponding to the separation is determined and the quotient is made of said force by the value of the contact area measured at the moment of the separation from the light totally reflected by said face.