Delta Metal
2 of the 6 encyclopedias on this shelf carry an entry for Delta Metal. Both are reproduced below, so you can see where they agree and where they differ.
The Encyclopedia of Founding (1892)
A gun-metal of great density and strength. Its composition is: copper 56, tin 1, zinc 41, iron 2. The wrought iron must be alloyed with the zinc in due proportion, and introduced as an iron-zinc alloy, in known proportions, in the customary manner. This alloy is similar to sterro-metal. An addition of lead (0.40 per cent) makes the composition more ductile and soft, and it is then called Tobin-bronze. Delta-metal can be forged or rolled at a dull-red heat, and may be drawn or hammered to a certain limit when cold. Castings made from this alloy are remarkable for their soundness, and have a tensile strength of from 40,000 to 50,000 pounds per square inch. See BRONZE. Density is the proportionate quantity of matter in bodies of a given magnitude; thus, if a body contain more matter than another, both being of the same bulk, the former is said to be more dense than the other. The quantity of matter is measured by the weight, and thus density and specific gravity come to be proportional to one another. Platina, which is about 21 times the weight of water, long passed for the densest body, but iridium is even more dense. Rare is opposed to dense; the rarest body known is hydrogen, which is about 14 1/2 times rarer than atmospheric air. Density of bodies is increased by cold and diminished by heat. See SPECIFIC GRAVITY.
Collier's New Encyclopedia (1921)
an alloy consisting of copper and zinc-in other words, brass-to which some manganese has been added in the form of ferro-manganese, or spiegeleisen, which contains manganese. A little silicon is but enough of this is usually present in also used, ferromanganese. Delta metal has similar properties to phosphor-bronze, if, indeed, some of it is not simply manganese-bronze. It is used for parts of machinery and for ornamental work.
What Has Changed in the Last Century
Both entries are describing Alexander Dick's patented trade product of the 1880s, and the fact that they disagree about it — the 1892 Encyclopedia of Founding gives copper 56, tin 1, zinc 41, iron 2, while Collier's in 1921 says the hardening addition is manganese by way of ferro-manganese — reflects that "delta metal" was a proprietary name covering several recipes rather than a fixed formula. That is exactly what has gone: the name has dropped out of engineering use, and the alloys themselves survive under standardised designations as high-tensile brasses and manganese bronzes, specified by composition and number rather than by trade name, and used for ship propellers, pump bodies and valve gear. The 1892 figure of 40,000 to 50,000 pounds per square inch tensile strength has also been left behind; modern high-tensile brasses of this family are routinely specified well above that. One incidental point in the 1892 digression on density has been corrected: iridium, named there as denser than "platina", is now edged out by osmium as the densest element known, the two being within a fraction of a per cent of each other.
Written for this edition, 2026.