Abstract: A power transmission system for a tractor comprising a hydraulic pump, a hydraulic motor to be driven by the oil forced out from the pump, a PTO transmission mechanism coupled to the shaft of the hydraulic pump and a wheel transmission mechanism coupled to the output shaft of the hydraulic motor. The power from an engine is transmitted to the PTO transmission mechanism by way of the pump shaft before being delivered to the wheel transmission mechanism.

Abstract: An aromatic polyimide resin composition useful for producing a film or sheet, comprises 2% by weight or more of an imide polymer having at least 90 molar % of a recurring unit of the formula (I): ##STR1## wherein R' is a divalent aromatic radical, and dissolved in an organic polar solvent consisting essentially of one or more halogenated phenol compounds of the formulae (II) or (III): ##STR2## wherein R.sup.2 is a hydrogen atom of a C.sub.1-3 alkyl radical and is a halogen atom, the halogenated phenol compound having a melting point of 100.degree. C. or less and a boiling point of 300.degree. C. or less.

Abstract: A device for tightening an endless element which is trained over driving members and which is accommodated in a drive transmission housing. A regulation member is provided outside the housing for easy adjustment of the tautness or tension of the endless element.

Abstract: A process for preparing a diester of oxalic acid which comprises bringing carbon monoxide into contact with an ester of nitrous acid in the liquid phase, in the presence of metallic palladium or a salt thereof, preferably with introduction of a gas containing molecular oxygen into the reaction system, more preferably with further incorporation of an alcohol in the reaction system.

Abstract: Disclosed is an epoxy resin composition containing, as an essential curing component, 2,3,3',4'-biphenyltetracarboxylic dianhydride which is highly compatible with epoxy resins at a relatively low temperature and effective for producing cured epoxy resins having an excellent thermal resistance.

Abstract: A process for the preparation of dialkyl oxalates by reacting an aliphatic alcohol with carbon monoxide under pressure, which comprises carrying out the reaction in the presence of(a) a catalyst comprising a platinum group metal or a salt thereof, and(b) an accelerator composed of one or more compounds selected from the group consisting of nitric acid and nitrogen oxides.

Abstract: A process for separating and purifying biphenyltetracarboxylic dianhydride isomers from a mixture of these isomers by fractional crystallization in aliphatic acid anhydrides or acetone. The isomeric mixture is obtained by heating biphenyltetracarboxylic acids, optionally in the presence of an aliphatic acid anhydride. The biphenyltetracarboxylic acids are obtained by oxidizing coupling dimers of o-xylene or by hydrolyzing coupling dimers of dimethyl phthalate. 2,3,3',4'-biphenyltetracarboxylic acid dianhydride which can be isolated from the above mixture can be used to form polyimide.

Abstract: A process for preparing substituted dibenzofuran or fluorenone-9 by the intramolecular cyclization of substituted diphenyl ether or benzophenone in the presence of a carboxylic acid salt of palladium and/or palladium organic complex.

Abstract: A process for separating and purifying biphenyltetracarboxylic dianhdride isomers from a mixture of these isomers by fractional crystallization in aliphatic acid anhydrides or acetone. The isomeric mixture is obtained by heating biphenyltetracarboxylic acids, optionally in the presence of an aliphatic acid anhydride. The biphenyltetracarboxylic acids are obtained by oxidizing coupling dimers of o-xylene or by hydrolyzing coupling dimers of dimethyl phthalate.