It’s worth noting that he claimed to “convert” 0.476 grains (30.8mg) per 10g of silver to gold. I do not know the origin of his silver samples, but trace gold is often found, even today, in silver samples, as well as chemical reagents. The purity of reagents available in 1925 was much lower than available today, and even today many reagents are commonly used at 95% or 99% purity.
As the junior guy in a lab back in the late 70s, I ordered the supplies. Lab chemicals aren’t nearly as pure as laymen imagine: 95% pure “technical grade” was often used because it was much cheaper than “reagent grade” (99-99.5% pure, depending on the chemical and supplier) and each higher grade could cost up to twice as much (or more) as the one before it.
Gold, being relatively inert, was usually considered a fairly innocuous contaminant. It is commonly mined with antimony, arsenic and silver ore. Gold contamination can be further increased by recycling: antimony and arsenic were both used in certain industrial gold extraction and purification processes, and gold is often found in silver jewelry. Believe it or not, before the gold boom of the late 1970s, gold cost ~$35/oz vs. $7 for silver (and more for many “pure” chemical reagents), so not only was the trace gold not worth the time/effort of recovery, but might actually act as a “cheap filler” for the purified reagent it displaced!
Therefore I would not be at all surprised if Ballandras actually only succeeded in extracting trace gold already present in his sample. His finding would correspond to ~0.3% contamination of the silver, and given that his process use (unreported, and very possibly greater) amounts of antimony and arsenic compounds, it could represent <0.1% of the total sample + reagents used. Also, in 1925, many chemists extracted their own reagents, if needed. Stibnite (Antimony sulfide, and a common antimony ore) was widely sold by pharmacists [Brit: ‘chemists’] and chemical houses in that era.
Leaving aside the charlatans, the same processs could have happened to even honest alchemists --especially since there were no reagent houses at the time, alchemists (and chemists as late as Ballandras in 1925) often extracted their own reagents from organic or mineral sources
An alchemist, working with “pure” antimony (which many considered a form of lead early in the alchemical age) could easily have extracted some gold, and spent the rest of his career trying to scale his process up to preparative scale [“scaling up to preparative scale” has been a common joke for generations of weary junior chemists and technicians, e.g. “Twas the night to make crystals” (1978)]. And thus was yet another “changing lead to gold” legend born.
Even as a kid, I always wondered why legend always had them starting with lead. Sure, lead was available since at least Roman times, but so were iron and many other metals. It’s possible that the natural association of antimony and gold (and their similar melting points) played a role.
Since Gold is relatively inert, any long series of extractions or separations might yield the hidden trace gold by removing everything else.