Electrical conductivity of air

The early pioneers also include Benjamin Franklin and Charles de Coulomb. Franklin studied the effect of point electrodes in drawing electric currents. Coulomb discovered that a charged object gradually loses its charge i.e., he actually discovered the electrical conductivity of air. Coulomb s importance for the development of electrostatic air-cleaning methods is great, mainly because the present theories about electric charges and electric fields are based on his work. 

In 1752 T. D Alibard and B. Franklin independently confirmed the electrical nature of thrmderclouds in the same year L. Lemomiier observed that electrical effects oc-cmred in fine weather. Not rmtil the late nineteenth cen-tiuy was the electrical conductivity of air established by several workers, and the discovery of cosmic ray ionization by V Hess and the postulation of the global electrical circuit by C. T. R. Wilson came in the early twentieth century. Now known as the classical global cir-... 

An fuel-air mixture explosion can be initiated by a sudden discharge of static electricity. Yet, while flowing in systems, a fluid develops an electrical charge which will take as long to dissipate as the fluid is a poor conductor. The natural electrical conductivity of jet fuel is very low, on the order of a few picosiemens per meter, and it decreases further at low temperature. 

Humidification. Adding moisture to air has long been used to control static and to help dissipate static electricity in textile mills (see A IR conditioning). Moisture does not improve the electrical conductivity of the air, but it increases the electrical conductivity of materials absorbing moisture. 

The combustion of mixtures of hydrogen and air produces very few ions so that with only the carrier gas and hydrogen burning an essentially constant signal is obtained. When, however, carbon-containing compounds are present ionisation occurs and there is a large increase in the electrical conductivity of the flame. Because the sample is destroyed in the flame a stream-splitting device is employed when further examination of the eluate is necessary this device is inserted between the column and detector and allows the bulk of the sample to by-pass the detector. 

FIGURE 3.9 The electrical conductivity of La1 xSrxCo03 3in air as a function of Sr doping, x. (From Petrov, A.N. et al., Solid State Ionics, 80 189-199, 1995. With permission.)... 

After Julius Elster and Hans Geitel had noticed that the electrical conductivity of the air in caves and closed cellars is higher than that in the free atmosphere, they finally found that this was caused by the presence of emanations, or radioactive gases, in the ground. In a series of investigations from 1901 to 1906 they demonstrated the presence of radioactive elements in various kinds of rocks and soils, and showed that minute amounts of both radium and thorium are widely distributed in the earth s crust, in spring waters, in sea water, and in the atmosphere (85, 96). 

P. Burckhard found that the electrolysisof tetrasodium pyrophosphate is attended by the evolution of much oxygen at the anode, and at the platinum cathode, gas bubbles are formed which inflame spontaneously in air, and platinum phosphide is formed. P. Walden found the eq. electrical conductivity of aq. soln. of tetrasodium pyrophosphate at 25° for soln. with one gram of the salt in v litres of water ... 

The electrical conductivity of water at 18°C is 0.04 x 10 reciprocal ohms (measurements of Kohlraush and IfeydweiUer, 1902) of pure water in equilibrium with air, 0.8 x 10-6 of ordinary distilled water, about 5 x 10- . 

The 3-4 Cals, here represent the heat of admixture of a mol of ammonia with water, and this is much greater than the heat of admixture of ammonia with other liquids which do not react chemically with the ammonia. There is also a possibility that ammonia hydrates. NH3.nH20, are formed, vide infra and a possibility that the ammonium hydroxide is ionized NH OH NH +OH. In agreement with the assumption that ammonium hydroxide is formed which acts as a weak base, the liquid tastes alkaline it reddens turmeric colours the juice of violets green and colours litmus, etc., the same as do soln. of the alkali hydroxides. These changes of colour disappear on exposure to air owing to the volatilization of the ammonia— the volatile alkali of the early chemists. The feeble character of ammonium hydroxide as a base is evidenced by its heat of neutralization with acids which is about 1-5 Cals, less than is the case with potassium or sodium hydroxides like other weak bases, the soln. cannot be satisfactorily titrated with phenolphthalein S. Arrhenius found that its effect on the hydrolysis of ethyl acetate is about 40 times leBS than that of sodium hydroxide and the electrical conductivity of aq. soln. of... 

The electrical conductivity of a solvent is generally very low, and is very sensitive to its purity. For instance, the absorption of carbon dioxide from the air... 

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