Electrostatic Machines

An important improvement of the single-ended Van de Graaff accelerators came through the replacement of the positive ion source inside the high-voltage terminal with an external negative ion source (Fig 14.6). 

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Electrostatic-Separation Machines The first electrostatic machines to be used commercially employed the principle of contact elec trification. These were free-fall devices incorporating large vertical plates between which an electrostatic field was maintained. Tribo-elec tric separation (contact charging) has experienced an increase in apphcations due to advances in mechanical self-cleaning and electrical design as well as the development of efficient precharging techniques. 

Viewing things from the perspective of his physical theory of contact electricity, Volta was intrigued by the apparently endless power of the battery to keep the electric fluid in motion without the mechanical actions needed to operate the classical, friction, electrostatic machine, and the electrophorus. He called his batteiy alternately the artificial electric organ, in homage to the torpedo fish that had supplied the idea, and the electromotive apparatus, alluding to the perpetual motion (his words) of the electric fluid achieved by the machine. To explain that motion Volta relied, rather than on the concepts of energy available around 1800, on his own notion of electric tension. He occasionally defined tension as the effort each point of an electrified body makes to get rid of its electricity but above all he confidently and consistently measured it with the electrometer. 

The importance of inflammable air became clear about fifteen years after Cavendish presented his paper. Joseph Priestley (1733-1804) was also interested in gases, and in 1781 told Cavendish of the results of some of his own experiments. When Priestley used an electrostatic machine to spark ordinary air with inflammable air, he noticed that water was formed. Cavendish repeated this experiment, as well as others like it, but using oxygen (or, as he called it, dephlogisticated air ) in place of ordinary air. 

We can also include thermal processes (such as a heat pump ), electric processes (an electrostatic machine, for instance), or chemical processes (such as a water electrolysis apparatus) in this (Fig. 2.4). However, because these kinds of processes are less familiar, we will come back to them later on in more detail. For now, we will limit ourselves to mechanical processes. 

The French abbot Jean-Antoine Nollet was interested in bioelectric phenomena and made use of electrostatic machines and Leyden jars for electrotherapy. His book Lettre sur Velectricite was published in Paris in 1753, and in it he referred to Franklins s work. It is said that under the French king Louis XV (reigned 1715—1774), the whole court se fait... 

Interestingly enough, for chemistry, one of the most thorough accounts of static electrical phenomena was that published by Joseph Priestley, The History and Present State of Electricity , London, 1767, in two volumes. It was an article in Encyclopaedia Britannica on the history of electricity by Tytler, copiously illustrated by diagrams of electrostatic machines, based in part on Priestley s volumes, that first stimulated Faraday to construct his first scientific instruments. 

Adriaan Pacts van Troostwijk (1752-1837) and Johan Rudolph Deiman (1743-1808), Dutch, and respectively a trader and a doctor, used an electrostatic machine using friction to generate electricity on two electrodes in or within a Leyden jar (the ancestor of the capacitor) filled with water. This was the first experiment with water electrolysis. 

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