Hunter later largely abandoned his work as a practical inventor and devoted himself to a futile (despite his claims of success) quest to transmute silver and other metals into gold.

Robert Hunter, an inventor in his own right, was granted seven US patents for marine propulsion systems (including one for a mechanical toy fish).

Lured by a $100,000 prize, he entered the boat in a New York State-sponsored contest to design a viable steam propulsion system for use on the state's canals.

Hunter's design featured two stern-mounted, vertically oriented paddlewheels that rotated in opposite directions, in order to control wake.

In 1874 Hunter took his newfound engineering skills to Olive Foundry & Machine Shops, in Ironton, Ohio, where he designed and built machinery.

In 1888 Frank J. Sprague completed the Richmond Union Passenger Railway, widely considered the first successful large-scale electric street-railway system.

In a December 1894 letter to Franklin Institute secretary William H. Wahl, Hunter intimated that the deal had netted him more than $600,000 (more than $15,000,000 in 2018 dollars).

[11] In 1894, hoping to gain recognition for his electric railway work, Hunter entered an annual competition conducted by the Franklin Institute's Committee on Science and the Arts.

[12] On his official entry forms, submitted a few days earlier, he was more realistic, claiming credit mainly for two of the electric street-railway's key elements: the "trolley system" (specifically, a viable underrunning trolley assembly) and the "series-multiple controller" (a speed- and torque-control switch, better known as the "series-parallel controller").

[13] A report on Hunter's entry concluded that other inventors had received at least partial credit for the underrunning trolley and that it was up to "the courts," not the Committee on Science and the Arts, to determine priority of invention.

Nearly two years earlier, the US Patent Office had granted priority of invention to Van Depoele, who had prevailed against both Sprague and Hunter in a landmark interference case.

Hunter, the examiner of interferences explained, had failed to show sufficient diligence in reducing his device to practice, prior to Hopkinson's date of invention.

His most important advance (though neither he nor Hunter, who acted as his patent attorney, realized it at the time) was to integrate the series-parallel and rheostatic methods in a single control mechanism.

[20] Hunter again entered the Franklin Institute competition, In 1896, claiming nothing less than to have invented the " 'step up and step down' transformer system of electrical distribution.

Marcel Deprez and Jules Carpentier, in a French patent application dated March 1881, had described the use of a step-up and step-down system to remotely activate a platinum filament.

[22] In 1898 prospects for the electric automobile seemed bright, and Hunter, armed with his electric-railway expertise, joined forces with prominent Philadelphia businessmen to launch General Electric Automobile Co.[23] The new company (which was not affiliated with GE) touted its control of 69 patents, over half of them Hunter's, that it claimed to cover virtually every element of value in battery-powered vehicles.

A committee had been appointed, in late March, to seek consolidation partners or secure "adequate working capital,"[27] and by mid May the company's stock price had collapsed.

[29] There is evidence of at least one more reorganization attempt, but the company does not appear to have conducted any significant business after the sale of its patent rights.

Hunter was probably not first to conceive such a vehicle; by 1899 Cleveland, Ohio-based Winton Motor Carriage Co. had converted an automobile into a tractor designed to tow a semi-trailer.

In so doing, he transformed the tractor from a source of motive power and directional control (essentially, a replacement for the horse) into an independent vehicle.

In a flurry of newspaper articles, the first appearing in July, he announced that he had discovered a process for changing silver (and other metals) into gold.

[31] He also announced plans for a $500,000 plant capable of producing "thousands of dollars worth of gold … daily,"[32] and he established two firms, Mirabile Corp. and United States Assay and Bullion Co., to implement the venture.

He had embraced the theory that atoms, instead of being fundamental units of matter (and therefore immutable), consist of yet smaller particles that, depending on their number (and other factors) comprise the different elements.

To create gold, he asserted, one needed only to deactivate the particles in silver atoms (by "de-electrifying" them), then "gather up 137,620 of them and impress upon them the proper electric charge … and set them into motion with new orbital range.

Just as Hunter was unveiling his transmutation claims, chemists William Ramsay and Frederick Soddy reported one of the most important findings of early atomic science.

In letters to his wife and, later, a good friend, Ramsay reported that Hunter was "no swindler" and had "based his conclusions on actual experiments."

It is hard to imagine, on the other hand, how someone with Hunter's expertise and experience could have failed to realize that his process did not work, so the possibility of fraud cannot be dismissed.

Hunter died March 19, 1935, at his home in Philadelphia, having never gained the level of recognition he sought as an inventor, and having never, apparently, renounced his transmutation claims.