Mercury pump technique

In the mercury pump technique, the volume of a 25-g sample of shale is obtained by pressuring a chamber to 24 psig with and without the shale sample. In the mtid balance technique, shale cuttings are added in the mud balance cup until they weigh the equivalent of a cup of water. The volume of shale can be expressed as... 

An oxygen-free solution (N2 or freeze and pump technique) of 333 mg (1.0 mmol) of 4.18a in 190 mL of dry benzene was irradiated with a Hanovia 450 W mercury vapor lamp equipped with a Pyrex filter (A, > 290 nm). Nitrogen was passed through the solution during the irradiation period of 30 min. The solvent was rota-evaporated and the residue purified on a column (20 x 2.5 cm silica gel, petroleum ether (40 - 70 °C)/toluene 1 1). A twofold recrystallization from ethanol afforded 225 mg (72%) of the cyclophane as colorless crystals, mp 296 C. 

Although anodic stripping voltammetry is one of the few techniques suitable for the direct determination of heavy metals in natural waters [310,756-764], it is not readily adaptable to in situ measurements. Lieberman and Zirino [623] examined a continuous flow system for the anodic stripping voltammetry determination of zinc in seawater, using a tubular graphite electrode predeposited with mercury. A limitation of the approach was the need to pump seawater to the measurement cell, while the method required the removal of oxygen with nitrogen before measurements. 

Vacimm Technique. There is a growing literature on ultra high vacuum technique by conventional methods (22). It will suffice to say that vacua of the order of 10 to 10 mm. Hg can be obtained readily with the use of either oil or mercury diffusion pumps. The crucial points are ... 

To remove any mercury deposits from a metal vacuum pump, it is important to check with the manufacturer because some cleaning techniques may destroy the pump. 

A Toepler pump is a piston pump with mercury as the piston. The mercury piston is powered by both the vacuum from a vacuum system and the atmosphere. The actual operation of a Toepler pump involves evacuation followed by readmission of air out of, and into, the Toepler pump. There have been a wide variety of techniques to automate this process because manual operation can be quite tedious. 

Low pressures can be achieved in a mechanical or "roughing" pump, by using a fluid (water, mercury, oil) in a rotating-vane technique to adsorb molecules within the fluid when exposed to the container to be evacuated, then expelling these molecules to the laboratory when the vane has brought the fluid into contact with laboratory air. 

Most of the experimental techniques for thermal systems apply here. One important exception is that for experiments using Hg 2537A radiation, the vacuum system must be completely free from mercury, i.e. no mercury diffusion pumps or McLeod gauges should be used, unless mercury-sensitised reactions are being studied. Even the use of iodine, gold or similar amalgamating metals does not completely free a particular section of the vacuum system from mercury. There is an excellent treatise on photochemical reactions by Calvert and Pitts. ... 

Although it is beyond the scope of this article to consider detailed collection and sample preparation procedures for environmental samples, here are some general considerations for speciation analysis of air, water, biological material, and soils/sediments. The collection of samples in air has focused upon the determination of hydrides and methylated compounds of elements such as arsenic, lead, mercury, and tin. The sample may be introduced into a preevacuated container, or with a pump. The analytes may be isolated using cryotrapping techniques or adsorbent cartridges. For best results, it is recommended to collect the entire gas sample in a container, coated... 

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