I came across the above complaint in Gleanings in Bee Culture
(1896). It seems that a door-to-door salesman was going around selling something he called "Prof. Humbolt's Electric-Light Fluid," which had absolutely nothing to do with electricity or electric lighting. The term "electric" was thrown into just about every product name back then to make products sound more scientific and modern.
As far as I can tell from the description, this "electric-light fluid" was a powder (not a fluid!) that people could add to the kerosene or coal oil in lamps. Supposedly it made the lamps burn brighter, smoke less, and reduced the risk of them exploding. Kind of like those fuel additives that are sold today that are supposed to increase your car's mileage per gallon.
Of course, as the complaint indicates, Prof. Humbolt's electric-light fluid did absolutely nothing, except separate people from their money.