I came across this in a patent search for something else. GB PATENT 339831A dated 18th December 1930. In the patent, a preamble refers to a tendency of existing silent burner caps to degrade (burn) over time, creating underburn as they get progressively hotter in use if they are not replaced soon enough. The patent does not specifically mention the phenomenon, but I think we’ve all noticed too that brass caps are inclined to glow red, giving the flames a red/orange tint, whereas steel csps do not. The patent states, Accompanying drawing. Presumably the alloy Hjorth refers to came to be known as Primus Metal. I see the French patent already appears in the Stove Reference Library/Patents HERE. John
Interesting patent John. I think this iron-nickel alloy (also known as Invar 36) mentioned by Hjorth above was the precursor to ‘Primus Metal’ but not the final composition. Some years ago I did some research into Primus Metal and while I could not determine the exact composition, the general opinion was that Primus Metal was an iron-based heat resistant alloy containing significant amounts of chromium as well as nickel - the chromium being a necessary addition to improve the high temperature oxidation resistance. A recent search gave the following comparison between Invar 36 and Primus Metal.
