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A historical fuel gas mixture made by destructive distillation of coal. Its composition depends on the feed and retort conditions; it is not synonymous with natural gas or pure methane.

The conventional nineteenth-century answer is diamond, graphite and so-called amorphous carbon. These exhibit strikingly different physical properties while sharing the same chemical element, carbon.

Diamond is a crystalline, usually transparent form, very hard and ordinarily an electrical insulator. Its three-dimensional covalent bond network joins each carbon chemical atom to four neighbours. Graphite is a dark, soft, crystalline form with layered bonding; easy shear between layers makes it useful for marking and lubrication. Its electronic structure permits much greater electrical conductivity than that of ordinary diamond.

The historical “amorphous” class includes charcoal, coke, lampblack and soot, as well as carbon-rich materials such as gas-retort carbon. Such names describe preparation and texture as well as structure: restricted-air heating of wood gives charcoal, destructive distillation of coal gives coke, and incomplete combustion of a carbon-bearing fuel produces soot. Modern structural examination shows that these materials can contain small, imperfect graphitic regions. They are not necessarily one distinct pure allotrope. Coal itself is a chemically complex, impure carbon-rich material, rather than a pure form of the chemical element.

A common chemical connection is that pure samples of these carbon forms can yield carbon dioxide upon complete combustion in excess oxygen:Their different hardness, appearance and electrical conductivity arise from structure and impurities, rather than from being different chemical elements. This is the explanatory role of allotropy.

Modern lists also include fullerenes, carbon nanotubes and graphene. These are useful present-day extensions, not discoveries to credit to the 1867 candidate.^[ref]

The wick supplies liquid wax by capillary action; wax vapour reacts with atmospheric oxygen, releasing the heat that keeps the supply going. The wick is a delivery system, rather than the principal fuel.

First, an external flame warms the wick and adjacent wax. Melting produces a small liquid reservoir, and capillary action draws it into the spaces between the wick fibres. Near the hot tip, evaporation and some pyrolysis supply gaseous fuel. Melting and evaporation are physical changes; pyrolysis and combustion change the chemical substances present. Once established, the candle flame transfers enough heat back to the wax to maintain this sequence.^[ref]

The candle flame is a diffusion flame. Its relatively dark inner region contains newly supplied fuel with limited access to oxygen. In the yellow luminous region, incomplete conversion of the hydrocarbons produces small soot particles, which become incandescent. Farther out, mixing supplies enough oxygen to consume most of the remaining fuel, carbon monoxide and soot. Thus the yellow light is largely thermal emission from hot particles, rather than a yellow gas.^[ref]

For a representative alkane component of paraffin wax, complete combustion has the chemical equationReal candle materials are mixtures, and some, such as fatty materials, already contain oxygen; the displayed chemical equation is an illustrative wax model. The principal products of complete combustion are carbon dioxide and water vapour. Convection carries the hot gases upward and brings fresh air into the flame. A cold collector can reveal condensed water; collecting the gases and passing them into limewater gives a calcium carbonate cloudiness from carbon dioxide.

Removing the oxygen supply, cooling the reaction zone, or cutting off wax delivery extinguishes the flame. The smoking wick immediately afterwards can still emit combustible vapour; without sufficient heat at the mixing zone, that vapour need not sustain a flame.

Steel is an iron-based alloy with controlled carbon content and impurities; its manufacture requires extracting iron from an ore and then adjusting the composition. In a modern plain-carbon classification, steel generally contains less than about $2\%$ carbon by mass, whereas pig iron is more carbon-rich. The historical practical contrast was with low-carbon wrought iron and readily cast but relatively brittle cast iron. Hardening by quenching is characteristic of suitable carbon-rich steels, but not every grade hardens in the same way.

Begin, for example, with an iron oxide ore. Preparation removes some earthy matter and, where appropriate, roasting expels moisture or converts a carbonate-bearing ore to oxide. A blast furnace receives the ore, coke and a flux such as limestone. The hot air blast sustains combustion of coke, generating heat and the carbon monoxide needed for much of the oxide reduction. Representative overall balances areCalcination of limestone provides calcium oxide. Combination with acidic gangue, represented by silica, gives a liquid slag:Actual slag is a multicomponent melt, rather than necessarily pure calcium silicate. The descending iron picks up carbon and other impurities and collects as molten pig iron. This first extraction product is not already finished steel.

Two important routes available in 1867 proceed from this stage. In the older indirect route, refining and puddling oxidize much of the carbon and remove slag-associated impurities to obtain wrought iron. Bars packed with charcoal are then heated for a prolonged period in the cementation process. Carbon enters the bars, giving blister steel; forging and welding can make shear steel, while melting suitable stock in covered crucibles produces more uniform crucible steel. The bar can acquire carbon through gas-mediated surface reactions and diffusion; the process should not be imagined as intact charcoal grains travelling through the iron.

In the Bessemer process, an air blast passes through molten pig iron in a converter. Oxidation of silicon, manganese and carbon supplies heat, while lowering the carbon content. Composition can be corrected by adding a controlled carbon- and manganese-bearing material such as spiegeleisen. Henry Bessemer's 1856 patent describes the central idea of maintaining the conversion by oxidizing constituents of the molten metal, without fuel for reheating during that stage.^[ref]

The early acidic converter demanded suitable feed: it did not solve removal of phosphorus from every ore. Later basic converter practice must not be silently imported into a December 1867 account. Final casting, working and heat treatment determine the steel microstructure and properties as well as composition. The useful manufacturing chain is therefore ore → extracted carbon-rich iron → controlled composition → worked and appropriately heat-treated steel.

The porous fuel-delivery component of a candle. Capillary action transports molten wax through its fibres to the region supplying gaseous fuel.