The Electric Spark

An electric spark is an electrical discharge across a gap between electrical conductors caused by a high potential difference across the gap. The voltage requirement depends on the gap dimensions and the shapes of the electrodes, but potentials of 10,000-50,000 V are common. 

Changes in inductance and capacitance change the frequency of oscillation in accordance with equation (5-1). An increase in either inductance or capacitance decreases the oscillation frequency. The current at the instant of discharge increases as the capacitance increases and decreases as the inductance increases. With large values of inductance and capacitance and the resulting decrease in oscillation frequency the spectra produced become more arc-like . By controlling inductance, capacitance, and resistance, a wide variety of excitation conditions are available. 

The condensed ac spark provides higher precision than does a dc arc, but with decreased sensitivity. Spectra produced by the ac spark contain a large number of ion lines as well as arc (atom) lines. Some doubly ionized species also are produced in a high-intensity ac spark. 

FIGURE 5-9. Circuit diagram of a high-voltage ac spark power supply. 

Several other methods have been employed to accomplish the same goal as the Feussner system. Commercially available spectroscopic power sources make use of the mechanical auxiliary gap, but more recently electronic devices have been constructed to control the spark discharge time. These devices can control the moment of discharge to within 1 /xsec and can be adjusted to produce discharge at almost any point on the time cycle. They result in highly reproducible, consistent spectra resulting in excellent analytical precision. 

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The extremely small quantity of the substance at my disposal did not permit me to isolate the new body from the excess of zmc accompanying. The few drops of zinc chloride m which I concentrated the new substance gave under the action of the electric spark a spectrum composed chiefly of a violet ray, narrow, readily visible, and situate at about 417 on the scale of wave lengths. I perceived also a very faint ray at 404 (4, 16). 

When one volume of olefiant gas is detonated by the electric Spark in a proper tube—which, on account of the violence of the explosion, should be very strong— with three volumes of oxygen, two of carbonic acid are formed, and water is deposited. Now two volumes of carbonic acid contain two of oxygon, so that the other volume of oxygen must have condensed two of hydrogen to form water. Hence one equivalent or volume of olefiant gas must contain two equivalents of carbon and two of hydrogen.—Brands. 

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... 

We may safely conclude, [be says] that in the present experiments the phlogisticated air was enabled by means of the electric spark to unite to form a chemical combination with the dephlogisticated air, and was-thereby reduced to nitrous (that is, our nitric ) acid, which united to the soap-lees and formed a solution of nitre.. .. A fur-thur confirmation of it is, that, as far as I can perceive, no diminution of air is produced when the electric spark is passed either through pure dephlogisticated air, or through perfectly phlogisticated air, which indicates the necessity of a combination between these two airs to produce the acid. ... 

When submitted, in a glass vessel, to the electric spark discharge, or when heated to 400° C., gradual decomposition sets in, with formation of sulphur dioxide and fluorine, the latter giving rise to silicon tetrafluoride, and the total change being representable by the equation ... 

In contact with air or oxygen the gas may be ignited either by a flame or by the electric spark. It burns with a bluish-white flame and is oxidised according to the equation... 

Table 3 shows the parameters of Al(OH)3 particles received by the electric spark discharge method. 

Figure 6. Dependence of the anti-microbe effect (ratio of the E. coli 1257 living cell number at given time Nt to the total number of cell No) of the electric spark treatment as a function of the external field strength Um and electric pulse frequency /...

Formic AcicL—Wilde 7 found that the action of the electric spark on gaseous mixtures of oxygen and alcohol, hydrogen and carbon dioxide, and methane and carbon dioxide, produced formic acid. In the first and last mentioned of these mixtures acetic acid is also formed. 

Cyanogen shows the same easy decomposability as hydrocyanic acid. Both Berthelot1 and Hofmann and Buff2 observed that cyanogen was decomposed into its elements by the action of the electric spark. The least trace of water in the gas caused the formation of hydrocyanic acid and acetylene. 

The observation of Morrens,3 who claimed to have obtained cyanogen in an atmosphere of nitrogen by passing the induction spark between two carbon electrodes, is therefore incorrect. The decomposition of cyanogen by the action of the electric spark has, moreover, been noted by Davy, and by Andrews and Tait.4... 

Acetone.—-Wilde4 investigated the action of the electric spark on acetone vapor in a Torricelli vacuum. Acetylene was formed in the gas mixture and carbon was deposited on the sides of the vessel. 

Methylamine. —The electric spark, when passed through methylamine vapor by Hofmann and Buff,5 gave primarily hydrogen and methylamine hydrocyanide further action brought about complete decomposition, tarry substances being deposited. 

The experiments carried out on the behavior of compounds of the aromatic series when subjected to the electric spark have so far given very few results. 

Aniline.—Destrem3 investigated the action of the electric-spark from an induction apparatus on aniline vapor, and observed a decomposition into acetylene, hydrogen, hydrocyanic acid, and nitrogen. 

Moritz Traube 4 rejected this explanation on the ground that carbon monoxide does not decompose steam at the temperature of the electric spark, for reaction (i) is reversible and under these conditions proceeds m the direction right to left. 

It appears that dephlogisticated water, or, which may be a better name for the basis of water and air, the element you [De Luc] call humor, has a more powerful attraction for phlogiston than it has for latent heat, but that it cannot unite with it, at least not to the point of saturation, or to the total expulsion of the heat, unless it be first made red-hot, or nearly so. The electric spark heats a portion of it red-hot, the attraction between the humor and the phlogiston takes place, and the heat which is let loose from the first portion heats a second, which operates in a like manner on the adjoining particles, and so continually until the whole is heated red-hot and decomposed.159... 

Methods for producing ammonia from its elements under the influence of the silent discharge and of the electric spark have not proved commercially successful.10... 

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