Positive charged steam ceased by adding small amounts of alkali to the distilled water. Replacing the distilled water with common London waters removed the steam charge. Ammonia added to distilled water produced charged steam, the steam able to redden turmeric paper, but the charge ceased after adding small amounts of sulfuric acid. Except for the latter, pH measurements of the steam were not reported in the Faraday experiments.
Negative charged steam was found by adding olive oil, and oils of laurel and turpentine to the distilled liquid water, but the charged steam ceased when the oils alone were present without the distilled water. If an alkali was added to the distilled water having olive oil, the steam lost charge, but not if added to distilled water having the oil of turpentine. Positive charged steam was found if sulfuric and camphor powder were added to distilled water. Faraday interpreted the pure distilled water droplets, the water globules coated with olive oil and oils of laurel and turpentine, and the powders of sulfuric and camphor as the rubbing agent and the nozzle as the rubbed surface, the sign of the steam charge sign depending on the tribo-electric series.
Faraday’s hypothesis is tenable for oils and powders that are physically different from globules of water and suggest different frictional levels and attendant tribo-electrical charging. But small amounts of acids and alkalis soluble in water could not be expected to alter the contact potential from that of distilled water and produce different tribo-electrical charging. Contrarily, acids and alkalis were found to indeed alter the steam electrification, a finding supportive of Armstrong’s contention that friction was not the exclusive cause of the steam electrification.
Faraday sought to eliminate steam altogether by working with compressed air. A container was pressurized with air from a syringe, the container providing a means to remove condensed moisture air before opening a valve to send the air against different materials. However, the procedure required extreme care to avoid oil contamination from the syringe. Both dry and common air were tested, the dry air obtained by leaving the compressed air in the container in contact with potassa fusa, a strong alkali for 10 - 15 minutes. Common air having moisture condensation was found to produce positive charge similar to steam; whereas, dry air failed to be electrified. Contrary to the contact electrification hypothesis, sulphur and silica powders in the compressed air experiments rubbing against wood and metal nozzles were found charged in opposition to their tribo-electrical order. Faraday expressed disappointment in not being able to explain why the tribo-electrical order was not found in the compressed air experiments
2. Scope, mechanisms, and purpose
2.1
Scope
In 1969, three large crude carriers were sunk or severely damaged by explosions that were thought to be caused by sparks from charge mist produced while their tanks were being washed with jets of hot and cold liquid water or steam ( see e.g. Jones and Bond, [7] ). Since Armstrong [1], steam has been known to be electrified, but because of the explosions during ship washing, wet steam was reaffirmed ( see e.g. Finke [8] ) as a source of highly charged mists. Hot and cold liquid water jets 2
also produce an electrified mist, but compared to wet steam do not pose a sparking hazard. On this basis, the scope of this paper is limited to electrification by wet steam.
2.2
Mechanisms
The interest of this paper is the mechanism by which the charge is produced in steam electrification, more commonly called spray charging. In 1972, Moore [9] discussed the prominent spray charging theories of Lenard [10] and Natanson [11].