Earthing precautions

An important point to be considered when the instrument is used for A.C. voltage measurement is the terminal connections. One terminal will be clearly designated as the high-potential connection, and this should be adhered to. The HT terminal will have a low value of capacitance to other bodies and to earth while the corresponding capacitance of the other is high. If the instrument is in a metallic case this should be connected to the mains earth as a safety precaution. In some cases, the low-voltage terminal is also connected to the metallic case. If this is so, the instrument will effectively earth the circuit under test, which may give rise to problems. 

If one of the structures to be bonded is the sheath or metallic armouring of an electric supply cable, special precautions will be necessary to ensure that the voltage rise at the bond in the event of an instantaneous earth fault on the power-supply system does not endanger personnel or equipment associated with other buried structures. The bond and any associated current-limiting device should be suitably insulated and of adequate current-carrying capacity. 

Because holmium is produced in such very small amounts, it is not a potential hazard to the general public. However, professional chemists take the same precautions as they do with other rare-earths. 

The same transformation was reported to follow treatment of 17 with excess sodium hydroxide (Sequiv), in aqueous acetone. In this case, the product yield was lower. With a reduced amount of alkali, 0.5 equiv KOH, both the hydroxy derivative 140 and the difurazanyl ether-linked bis(triazolooxadiazole) 37 resulted (Scheme 21) <1999RJ01525>. As a precaution it should be noted that the strongly acidic nature of hydroxyfurazans means they readily form stable salts with amines and alkali or alkaline earth metals, and such salts show a tendency to decompose with explosion on shock, friction, or fast heating, and so should be handled with care <1999RJ01525>. 

For solutions containing sulphuric acid or a sulphate the reagent commonly applied is barium chloride, both when the test is to be qualitative and when quantitative. Precipitation is effected by the gradual addition of barium chloride to the boiling solution containing a little hydrochloric acid, but for the production of pure barium sulphate, and therefore in order to ensure accuracy, certain precautions must be observed.4 Nitrates, perchlorates, phosphates, tervalent metals and large quantities of salts of the alkali metals (particularly potassium) and of the alkaline earth metals are to be avoided, as they cause the precipitated barium sulphate to be rendered impure by occlusion of otherwise soluble substances.5 Such impurities may be accounted for partly by... 

Corbette-type Magazine. This is a beehive or dome type magazine having the front rear, as well as the sides, covered with earth as an extra precaution in the event of an explosion. The magazine is provided with ventilators and is protected against lightning by an efficient... 

When found, the bomb should be handled with great precaution and not be turned upside down, because some bombs, (called "bombes a ren-versement ) explode on such movement. In order to prevent anybody else from such an action, the upper part of the bomb should be marked with chalk or pencil. Then the bomb is moved carefully into an excavation dug in a field, a cartridge of Dynamite or Tonite (provided with a primer and a 100 meter long piece of fuse), is placed over it and the ensemble covered with earth. Detonation of the cartridge explodes the contents of the bomb and shatters it to pieces... 

Most of the development data that are suitable for theoretical interpretation, however, are acquired with rare earths. Fortunately, such data can be transferred to actinide separations with great confidence, as long as certain precautions are taken. 

The Group 7 metals technetium and rhenium have not been applied to the problem of oxidation chemistry to the level of their Group 6 and Group 8 counterparts. This is understandable in light of their relative scarcity. Technetium is a synthetic element, recovered as a fission by-product from uranium.3 "Tc is radioactive (/3 decay, 0.3 MeV, tv2 = 2.14 X 10s years) and its use even in the laboratory requires the appropriate safety precautions. Rhenium is not plagued by either issue, yet it is still a relatively rare element, present at only an estimated 0.001 ppm in the Earth s crust. It is... 

Technetium was the first of the artificially produced elements (1937) when it was obtained, as the isotopes 95Tc and Tc, by bombarding Mo with deuterons. Today twenty-one isotopes, all radioactive, are known with mass numbers 90-111. The longest lived isotope is Tc (ha 4 x 106 y), but the commonest is "Tc (tm — 2 x 105 y). It is isolated in fairly large quantities from spent nuclear fuel, where it constitutes ca. 6% of the fission products. The total amount of "Tc is about 78 tons, which exceeds the known amount of rhenium in the earth s crust. "Tc emits a soft (293.6 Kev) /3 particle and can be handled with only very modest precautions. 

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