Abstract: This invention relates to an improved method and apparatus for preventing cross-contamination of biochemical test wells included in a microtiter test plate which comprises the covering of the biochemical test wells with a porous barrier that has been impregnated with an approximately 10% (W/V) solution of a solid, water soluble compound and then dried before use, the impregnating material being one selected form a group of chemical compounds consisting of inorganic acid phosphates, the acid salts of amino acids and the polycarboxylic organic acids which are relatively non-volatile, non-hygroscopic and non-toxioc to humans and bacteria while remaining effective to neutralize alkaline gases without attacking the barrier material.

Abstract: This invention relates to a double-acting drilling jar characterized by a constantly recharged hydraulic system operating in concert with a mechanical brake to actuate the latter and temporarily inhibit extension of the relatively moving parts utilizing a modest fluid pressure multiplied many-fold so as to exert a holding force far in excess of that which the hydraulic system could impose alone without destroying the seals. The invention also encompasses the virtual elimination of heat build-up through the use of drilling mud as the working fluid in a hydraulic system where once-used fluid is discharged downhole before it gets too hot while, at the same time, being replaced by a fresh supply of cool fluid from the surface. By calling upon the hydraulic system to only exert enough force to actuate the mechanical system, none of the fluid seals need be loaded to anywhere near their capacity.