Follow-up Q12 (2026-10-08): Le Bon's "radioactive" amalgamated tin

Question (owner, recorded 2026-10-07). Le Bon (The Evolution of Matter, 1909; Rex Research full text) says mercury and tin each give off very little "radioactivity" in light. But mercury with 1/1000 of its weight of tin, or a tin strip soaked 24 hours in mercury (amalgamated tin), becomes "extraordinarily radioactive" in sunlight. In his electroscope table amalgamated tin discharges fastest (1000, against 2 for gold, pure mercury and tin), but only when charged negatively. Was this radioactivity or the photoelectric effect (Hallwachs 1888: ultraviolet light knocks electrons out of a metal, so only a negative charge leaks away; amalgamation cleans the surface and lowers the work function)? Did anyone repeat Le Bon's amalgam experiments, and how were they received? Do Moray's books (Radiant Energy, The Sea of Energy, the Isotopes booklet) rely on or repeat Le Bon's amalgam claims? Does any of this bear on Moray's detector or on Ives's thin-film photoelectric work (alkali metals and standing waves)?

Web time: about 5 minutes (Chrome: 8 Google searches. Curl: Copernicus HGSS PDF, Project Gutenberg (Lodge; L. Poincaré), arXiv (Kragh), Rex Research (Evolution of Forces Part II), Internet Archive full texts (Phil. Mag. 1906 and 1907; The Athenaeum 1906), E-CatWorld). I stopped early because the question was answered. Saved pages are in research/pages/.

Terms. Electroscope: two gold leaves that spread apart when charged; the rate at which they fall back measures the current that leaks away. Photoelectric effect: light ejects electrons from a surface when each photon's energy hf (Planck's constant h times frequency f) exceeds the surface's work function W. W is the minimum energy needed to pull one electron out, a few electron-volts (eV) for metals. A photon of wavelength λ carries E = 1240/λ[nm] eV, so 295 nm gives 4.2 eV and 360 nm gives 3.4 eV. Amalgam: an alloy or solution of a metal in mercury.

What was searched

What was found

1. What Le Bon wrote [web https://www.rexresearch.com/lebonmat/lebonmat.htm, Book V experimental part; Legge translation]: - Chapter "Experiments on the Possibility of Rendering Bodies Radioactive which are not so": "bodies presenting only traces of radioactivity under the influence of light, such as mercury, can, on the other hand, become extremely radioactive. It is sufficient to add to this metal a 1/1000 [1/5000 ?? --- the text is illegible] its weight in tin". With that much tin the mercury responds only to "the solar ultraviolet from 0.360 microns to 0.296 microns"; with 1% tin, "most of the rays of the visible spectrum". The strip: tin "10 cm square and 2 cm thick", fastened to cardboard and "plunged for 24 hours into a bath of mercury". In the lecture experiment (his Figure 45) the strip is not on the electroscope. The electroscope "is inductively charged by an ebonite rod; its charge is, in consequence, positive", and the sunlit strip makes the leaves fall "in a few seconds". A uranium-nitrate screen of the same size gives "about 6 degrees in 60 seconds"; the amalgamated tin mirror gives "40 in 10 seconds". Hence his conclusion that "artificial radioactivity given to a metal by light may be 40 times greater than the spontaneous radioactivity possessed by salts of uranium". From Rutherford's 70,000 particles per second per gram of uranium he then estimates "3,000,000 particles/second". - In the theoretical part: "Two bodies not radioactive sometimes become so when combined. Mercury and tin may be placed among bodies of which the dissociation, under the action of light, is the weakest; I have shown, however, that mercury became extraordinarily radioactive under this same influence, so soon as traces of tin are added to it." - Chapter V, "Experiments on the So-Called Negative Leak Caused by Light in Electrified Bodies". He sets out the received view: the leak needs ultraviolet, is "the same for all metals", and "only takes p[l]ace when the charge of the metal is negative". He adds that "Elster, Geitel, and Branly, it is true, mentioned some time ago two or three metals which discharged in ordinary sunlight", and claims three propositions "exactly contrary": the leak is also positive, though weaker; it occurs in several spectral regions; and it differs greatly between bodies. His table, "Rapidity of the Negative Leak in the Solar Light", has the strip lying on the electroscope plate: amalgamated tin 1000, amalgamated zinc 980, clean aluminum 800, amalgamated silver 770, clean magnesium 600, clean zinc 240, amalgamated lead 240, cadmium 14, cobalt 12; "Gold, steel, copper, nickel, mercury, lead, silver, phosphorescent sulfides, carbon, marble, wood, sand, etc. = 2 maximum". The positive leak in sunlight is "very weak (1 degree at most in 1 or 2 minutes)". Under electric-spark ultraviolet the negative leak runs aluminum 1000, amalgamated tin 680, ... tin 270. The positive leak there is 7-16 per minute. - Spectrum and cleaning. For amalgamated tin or aluminum in sunlight, 85% of the action comes from 0.360-0.29 µm and only 6% from wavelengths above 0.400 µm. Tin, cadmium, silver and lead "become very Sensitive only to Radiations having Wavelengths less than 0.295 microns". Metals in sunlight must be cleaned with emery "every 10 minutes", "under the penalty of seeing the discharge become 200 times less rapid". Amalgamated tin strips need "no cleaning" for "about a fortnight". - Le Bon himself says his "effluves" are Lenard's and J. J. Thomson's particles: "Lenard and Thomson have, since my researches, made this identity indisputable by ... measuring the ratio e/m", which "has been found to be identical with that observed with the cathode rays". He gives the dates of his priority claim: Lenard's memoir of 18 Oct 1899 against his own Comptes rendus note of "5th April 1897". - Correction to the question's wording, for the record: in the solar negative-leak table it is mercury (pure) and gold that score "2 maximum". Plain tin is not in that table. It appears in the earlier "least sensitive" list (1-9 degrees per minute) and scores 270 under spark light. "Only when charged negatively" holds for the strip-on-electroscope table. The Figure 45 lecture experiment uses a positively charged electroscope with the strip apart from it (see inference 1).

2. Elster and Geitel had the amalgam result in 1889-90, about ten years before Le Bon. Lodge's appendix abstracts their Wied. Ann. 38 papers (1889). Sunlight discharges a negatively charged zinc dish; "A positive charge of 300 volts is retained". Then: "A still more notable sensitiveness to light is shown by the amalgams of certain metals, viz., in the order of their sensitiveness, K, Na, Zn, Sn. Since pure mercury shows no effect, the hypothesis is permissible that the active agent is the metal dissolved in the mercury." The footnote gives drops of amalgam falling through a funnel: pure mercury fell from -185 to -175 V in 30 s, zinc amalgam from -195 to -116 V in 15 s, sodium amalgam to 0 in 10 s, potassium amalgam to 0 in 5 s. Amalgamated zinc "negatively charged, discharges almost instantly in sunlight; and if near a positively-electrified body charges itself positively" [web https://www.gutenberg.org/files/69253/69253-h/69253-h.htm, Lodge, Signalling Across Space Without Wires, 3rd ed., London: The Electrician]. Their solar-UV actinometer was a "light-protected, amalgamated zinc sphere ... negatively charged, the light incidence is enabled and the charge loss is monitored on the electrometer" (Elster and Geitel 1892), made commercially by Günther and Tegetmeyer [web https://hgss.copernicus.org/articles/8/1/2017/hgss-8-1-2017.pdf, Fricke and Schlegel 2017, Fig. 3]. Le Bon's apparatus and materials were therefore the standard photoelectric actinometer of the 1890s. Mercury-plus-a-dissolved-metal (including tin) was already known to be the sensitive combination.

3. Ramsay and Spencer repeated Le Bon's experiments in 1906, including tin amalgam, and confirmed the rates. "The work communicated in this paper was undertaken with the object of repeating some experiments of Le Bon ... previous to Le Bon's publications some of his results had been anticipated, among others by Elster and Geitel, Hoor, Stoletow, Wiedemann and Ebert, Hallwachs, Righi, and Branley." Their findings: - "plates of zinc amalgam and tin amalgam gave discharges much too rapid for accurate measurement", so copper amalgam served as their standard. - Table IX (saturated amalgams; OCR of the element names is garbled for the first rows) gives mercury 216 s, tin amalgam 0.6 s, zinc amalgam 0.7 s, copper amalgam 10.0 s. "The effect of alloying one metal with another does not seem to give the mean of the two values." - Two of Le Bon's claims did not reproduce. "On reversing the charges, we were unable to get a measurable discharge", so no positive leak was measurable in their arrangement. "It was found impossible to discharge the electroscope if any of the metallic shields were used", so nothing came through Le Bon's aluminium screen. They attribute this to their weaker iron-arc and mercury-lamp sources against Le Bon's high-tension sparks. - Their interpretation went beyond Le Bon's: emission of corpuscles "denotes a disruption or disintegration of the atoms", and "it may be that the residual matter, the zinc minus electrons, is no longer zinc", a possible "transmutation". [web https://archive.org/details/londonedinburg6121906lond, Phil. Mag. S.6 vol.12 no.70, Oct 1906, pp.397-418 (Le Bon discussion pp.401-402, 404; Table IX p.413)]. Le Bon cites this in The Evolution of Forces as "identical with my own" and says Ramsay "entirely admits the theory of the dissociation of matter" [web http://www.rexresearch.com/lebonfor/evforp2.htm]. In The Evolution of Matter he cites it for the law that dissociating power rises as penetration falls [web Rex, Book V ch. on the spectrum].

4. Reception: the effect was accepted as the photoelectric effect; Le Bon's and Ramsay's "dissociation" reading was not. - Millikan and Winchester, "The Influence of Temperature upon Photo-electric Effects in a Very High Vacuum, and the Order of Photo-electric Sensitiveness of the Metals" (Phil. Mag. S.6 14, July 1907, from p.188), treat Ramsay and Spencer's results as photoelectric. Photoemission does not depend on temperature, so "it is not these [free] electrons which escape", and Ramsay and Spencer's two-stage account of fatigue (metallic electrons first, then electrons "thrown off from the body of the atom") is excluded. The sensitivity order in air "shown by Elster and Geitel's and Ramsay and Spencer's experiments, is doubtless to be accounted for" by a surface double layer formed with oxygen; in vacuum the effect bears "no relationship whatever to the Volta contact series" [web https://archive.org/details/londonedinburg6141907lond]. - Norman R. Campbell (Trinity College, Cambridge), letter "Dr. Le Bon's Theories of Matter", The Athenaeum no.4086, 17 Feb 1906, pp.202-203. It was part of a correspondence indexed at pp.202, 237, 269, 303, 333, 366; only Campbell's letter was read. Campbell writes that "his experiments are perfectly inadequate to prove his theory under any interpretation". On the light experiments: radioactivity is "absolutely spontaneous and unaltered by any process", yet "To prove that all bodies have this property, Dr Le Bon tells us that they become active when exposed to light and heat!" He also says "A great many of his results were known already". He re-explained one of Le Bon's new phenomena, and "Mr. Carse has tried and failed completely to repeat another" (which experiments is not stated in the part read). Campbell also says he does "not doubt that the theory which he advocates now is in the main correct", meaning general radioactivity and atomic instability [web https://archive.org/details/p1athenaeum1906lond]. Campbell was an interested party in the sense of a rival worker: he measured the weak natural radioactivity of ordinary metals in 1905-06 [memory, medium]. - Kragh (2012): Le Bon's "black light turned out to be imagination rather than reality - most physicists failed to detect the rays". For a while he was "an important figure in French scientific and intellectual life", and "In 1903 he was even nominated for the Nobel Prize in physics" [web https://arxiv.org/pdf/1208.3114, pp.13-14]. Nye 1974 (Historical Studies in the Physical Sciences 4:163-195) is the detailed study. It is paywalled and was not read.

5. Modern photoelectric reading of Le Bon's own numbers [calc, with memory values marked]: - Threshold. Solar ultraviolet at the ground ends near 0.295 µm (Le Bon's own limit), that is 4.2 eV. Clean tin and mercury have work functions of about 4.4 and 4.5 eV [memory, medium], so sunlight barely reaches them. That matches Le Bon's "tin ... only sensitive below 0.295 microns" and the "2" for mercury. Zinc (about 4.3 eV), aluminium (about 4.1-4.3 eV) and magnesium (about 3.7 eV) [memory, medium] sit at or below the solar cut-off and lead his table, as the photoelectric picture predicts. Amalgamated tin responding at 0.296-0.360 µm means an effective work function of 3.4 eV or less. - Sign. In the strip-on-electroscope table the illuminated metal is the electroscope, so only a negative charge leaks (Hallwachs). In Figure 45 the strip is separate and the electroscope is positive. Electrons ejected from the strip are pulled to the positive electroscope and neutralise it, the arrangement Elster and Geitel described ("if near a positively-electrified body charges itself positively"). Both results are what the photoelectric effect predicts. The "positive leak" from the strip itself is weak in Le Bon's own data and was not measurable for Ramsay and Spencer. - Cleaning. A factor of 200 lost to oxidation in ten minutes, against a fortnight's stability for a mercury-wetted surface, is what one expects if a surface film raises the work function. Millikan and Winchester gave the same oxide-layer explanation. Why tin in mercury beats either metal alone is not settled by the sources found. Readings: (a) a fresh, oxide-free, self-renewing liquid-metal surface (Elster and Geitel's "the active agent is the metal dissolved in the mercury"); (b) a lower work function at the amalgam surface; (c) traces of more active metals in commercial tin or mercury. None of the sources tested (c). - "40 times uranium" compares two different currents, not particle counts. The uranium screen discharges the electroscope by alpha particles ionising the air. One U-238 alpha (about 4.2 MeV) makes about 4.2 MeV / 35 eV ≈ 1.2 × 10^5 ion pairs [calc; 35 eV per ion pair in air, memory, high]. A photoelectron carries one electron charge and less than 1 eV of kinetic energy. Per unit of current, the photoemitting strip therefore releases about 10^5 times more particles than the uranium does. Per particle, the energy is about 10^6-10^7 times smaller. Le Bon's step from 40 times the current to "3,000,000 particles/second", treated as like radioactivity, mixes these two. - Size of the energy. Assume an electroscope of about 10 pF charged to about 1,000 V (not given by Le Bon), that is q = CV = 10^-8 C, and Le Bon's "40 [degrees] in 10 seconds" taken as most of the charge. The photocurrent is then of order 10^-9 A (1 nA). At a stopping potential below 1 V that is at most about 1 nW from 100 cm² of sunlit amalgam, while the sunlight on that area brings about 10 W [calc; assumptions stated].

6. Moray does not repeat the amalgam experiments, but he copies Le Bon's thesis that the light-driven charge loss is dissociation. No passage in the extracted text of Radiant Energy, The Sea of Energy (4th ed., 5th ed., Pepe/Tesla pages) or the Isotopes booklet mentions amalgamated tin, tin in mercury, or Le Bon's electroscope tables [read: grep of _text/ for amalgam, mercury, tin, electroscope]. What he does copy: - Radiant Energy printed p.46 (pdf p.47), from Le Bon: "the loss of an electric charge occasioned by ultra-violet light has long been known, but not one little thought connecting the fact with cathode rays ... The loss of electric charges through the influence of light had been kn[own] for many years but it was regarded as a fact peculiar to a few metals with no suspicion of how general and important this law was. All this phenomena ... are the consequences of the same fact--namely, the dissociation of matter" [read: _text Radiant Energy pdf p.47]. The same passage is in Sea of Energy 4th ed. (pdf p.68) and 5th ed. (pdf p.220), "long-been known but not the thought connecting this fact with a cathode ray" [read]. - Isotopes booklet pdf p.7 (also Le Bon) lists "the decomposition of water by zinc and sulphuric acid or merely by the sodium amalgam" among chemical reactions that "reveal a dissociation or change of matter". That is Le Bon's chemical "effluve" experiment (an electroscope near hydrogen evolving from sodium amalgam and water, "Loss, 9 per minute"), not the light experiment [read: _text Isotopes pdf p.7; web Rex]. - Elsewhere Moray uses the mainstream term. Radiant Energy pdf p.30 lists "Photo electric ionization by ultraviolet light, X-Ray and othe[r] rays" and "Action of gamma rays, X-rays and light on solid or liquid surfaces giving electrons photo-electric effect" [read]. The 4th and 5th editions repeat it [read]. - The sons' 5th edition says Henry "became deeply involved particularly in the study of synthetic radioactivity as described by Gustave LeBon in his book, The Evolution of Matter", found the book withdrawn from libraries, and drew FBI questions [read: _text Sea of Energy 5th ed. pdf p.187]. Le Bon's chapter on making non-radioactive bodies radioactive, the chapter with the amalgamated tin strip, is one candidate for "synthetic radioactivity" (see inference 3).

7. Related work in the project folder: Plauson's atmospheric collector used photoelectric amalgams. The Nuenergy compilation reproduces Hermann Plauson, US 1,540,998 (9 June 1925): "The small circles on the collector balloon indicate places at which zinc amalgam or gold amalgam or other photoelectric acting metals in the form of small patches in extremely thin layers (.01 to .05 mm. in thickness) are applied to the balloon casing ... The greatest possible effect in collecting may be obtained by polonium amalgams and the like" [read: _text zz-Misc Nuenergy pdf p.83]. This is the Elster-Geitel amalgam photocathode used on an atmospheric-electricity collector, in the same family as Moray's antenna-and-ground claim (Claim 3).

8. Ives. Ives's 1924 thin-film paper starts from Elster and Geitel: "Elster and Geitel observed that the alkali metals, when placed in well-evacuated inclosures, quickly coat all parts of the inclosures ... with a photo-sensitive layer" [read: Ives project _text Ives 1924, lines 42-47]. His 1926 Bell System Technical Journal paper calls the commercial cell "the alkali metal photoelectric cell as developed by the work of Elster and Geitel and others" [read: Ives project _text Ives 1926 BSTJ]. Elster and Geitel's amalgam series (K, Na, Zn, Sn) is the start of the line that led to Ives's alkali cells. Ives's own contribution was different: the "selective" photoeffect of alkali films a fraction of a wavelength thick, explained by standing light waves in the film. That depends on film thickness and optics, not on what the metal is dissolved in (Ives arbiter, "Material kept in the record"). Mercury appears in Ives's 1951 lecture only as Lippmann's mirror, which sets up standing waves in a photographic emulsion [read: Ives 1951 lines 650-664].

Reasoning and answer

• Radioactivity or the photoelectric effect? By every test the sources allow, the photoelectric effect:
• the spectral threshold near the solar ultraviolet limit;
• the sign dependence, including the Figure 45 arrangement;
• the strong dependence on surface cleanliness;
• Le Bon's own identification of his particles with Lenard's and Thomson's electrons (same e/m);
• the order of the metals.

Elster and Geitel had published the amalgam result, including tin and the inactivity of pure mercury, in 1889-90. In 1906 Ramsay and Spencer confirmed that tin and zinc amalgams discharge an electroscope fastest. In 1907 Millikan and Winchester treated the same measurements as photoelectric and explained the order of the metals in air by surface oxide layers. Le Bon's word "radioactivity" meant emission of electrons provoked by light. That differs from radioactivity as Rutherford defined it, which is spontaneous and cannot be switched by light, as Campbell objected in 1906. Le Bon was right on facts that were also right in the photoelectric literature: many bodies emit, and the response varies greatly from body to body. His novel claims were the positive leak and penetration of metal screens. Ramsay and Spencer could not reproduce either with their sources. - Repeated? Yes: anticipated by Elster and Geitel (1889-92), repeated by Ramsay and Spencer (1906), reinterpreted by Millikan and Winchester (1907). Reception in Britain was harsh on Le Bon's claims of priority and interpretation (Campbell 1906). Ramsay accepted a "disintegration" reading for a time, and Le Bon advertised that acceptance. - Moray. He does not use the amalgam claims in the texts read. He copies Le Bon's broader claim that the light-driven charge loss is "dissociation of matter", and elsewhere uses the mainstream term "photo-electric effect". - Moray's detector. The reported ingredients (germanium, bismuth, iron sulfide, molybdenite, triboluminescent zinc, radium chloride; claims.md Claim 4) contain no mercury or tin. A photoelectric amalgam supplies nanoamperes from sunlight (finding 5), so it cannot account for the kilowatt claims. The one direct use of photoelectric amalgams on an energy collector in the folder is Plauson's (finding 7). - Ives. A shared ancestry (Elster and Geitel's photosensitive metals) but no shared mechanism. Ives's standing-wave effect concerns thin alkali films and optics; Le Bon's concerns surface chemistry.

Competing readings (inferred)

1. Le Bon's Figure 45 positive-electroscope discharge is photoemission from the sunlit strip collected by the electroscope. This is consistent with Elster and Geitel's "charges itself positively" (the strongest reading on the evidence). Alternative: ionised air near the illuminated strip. That is less likely in sunlight, which does not ionise air (Le Bon's own Lenard citation puts air ionisation below 0.185 µm).
2. Why the tin-in-mercury amalgam beats both components: (a) a fresh, oxide-free liquid surface; (b) a lower work function at the amalgam surface; (c) traces of more active metals. Not decided by the sources read.
3. "Synthetic radioactivity" in the sons' book: (a) Le Bon's light-provoked radioactivity (the amalgam chapter); (b) Le Bon's "induced radioactivity" of thorium deposits (Q11); (c) radioactivity "provoked" by chemical reactions such as quinine hydration, which Moray copies on Radiant Energy p.58. The phrase does not say which. All three are in the chapters Moray copied.

Leads (for sites.md, follow-up Q12)

• Priority 2/3: Elster and Geitel 1889-92 amalgam photocathodes; Ramsay and Spencer 1906 repetition of Le Bon; Millikan and Winchester 1907.
• Priority 3: Plauson US 1,540,998 photoelectric amalgam patches on the collector balloon (already in folder).
• Priority 4 (reception record): Campbell, Athenaeum 17 Feb 1906, and the rest of that correspondence (pp.237-366, not read); Nye 1974 HSPS 4:163-195 (paywalled); "Mr. Carse" failed repetition (unknown which experiment).
• Peripheral: E-CatWorld 2019 post quoting Le Bon's "Rendering Bodies Radioactive" chapter alongside Cardone et al., "Nuclear metamorphosis in mercury", Int. J. Mod. Phys. B (2015), a modern claim of transmutation in mercury (not read).

Corrections to earlier documents

None to the review files. The question text recorded on 2026-10-07 has two small inaccuracies, noted in finding 1 so the answer does not repeat them: - In the solar table it is pure mercury and gold, not tin, at "2 maximum". Tin is in the "least sensitive" list and scores 270 under spark light. - The Figure 45 lecture experiment uses a positively charged electroscope.

The question is kept as asked, so it is left unchanged.