Electrical spark-over

Nitric acid was known to alchemists in ancient times. Cavendish in 1784 synthesized the acid by applying an electric spark to humid air. Earlier in 1776, Lavoisier determined that the acid contained oxygen. In 1798, Milner prepared nitric acid from ammonia along with nitrogen oxides by oxidation of ammonia vapor over red-hot manganese dioxide. In 1816, Gay-Lussac and Berthollet established its composition. 

In discussing an experiment by Priestley—in which an electric spark passed through air confined over litmus solution in an inverted U-tube produced an acid reaction on the litmus (oxidation of nitrogen to nitrous acid)—Bergman makes this interesting statement ... 

Another important discovery by Cavendish is based upon an observation of Priestley. Priestley had experimented by passing the electric spark through air confined over water colored with litmus, and found that the air was diminished in volume and that the litmus was reddened. As Priestley believed that electricity was another form of phlogiston, his results were puzzling to him. His curiosity excited by Priestley s observations, Cavendish also attacked the problem. This resulted in his proof that, by this means, practically all the phlogisticated air could by a sufficient... 

About 1775, J. Priestley 2 passed a series of electric sparks through atm, air confined in a suitable vessel over water coloured purple by a decoction of turnsole or archil. He found ... 

Current fluctuations are damped by means of choking coil D connected in series. The rectifier starts operating by means of auxiliary electrode H which is connected to anode. 1, over the resistance W. When the rectifier is started it must be tilted so that the two pools of mercury accumulated at H and K merge into one. On restoring the rectifier to its normal position the pool of mercury is divided once again in two parts and gives rise to an electrical spark at the point of interruption the heat evolved by the spark causes that a certain amount of mercury, sufficient to ignite the arc, evaporates. 

As another example that relates to comparisons between processes executed reversibly or irreversibly, consider at constant volume the conversion of hydrogen and oxygen into steam over a platinum catalyst, and compare this with the explosive conversion by an electric spark. Are any changes needed in the derivations ... 

The gas is colorless, odorless, nontoxic, and inert. It is not changed by electrical stress just below the corona point (82), but it is decomposed slowly by spark-over or corona electrical discharge (82, 272) giving lower fluorides of sulfur and fluorides of the metals used as the electrodes. It does not react with water or with a basic solution but it does react vigorously with a hot alkali metal. The gas is not toxic however, it has some depressant action upon the central nervous system (45) and has mild anesthetic properties (812). In spite of this, rats may live in an atmosphere of 80% SF6 and 20% 02 for periods up to one day with no signs of poisoning (187). 

The compound CSHF7 reacts readily with NaOH solution to give F and other products. It decomposes in a spark-over electrical discliarge to give CF4, CHF3j and SF4 (279). 

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