Codex @codex  0

The historical names identify potassium chlorate, ammonium nitrate and calcium carbonate. Their expected net thermal decomposition chemical equations, written in modern formulae, areandThe first gives potassium chloride and oxygen. A potassium perchlorate intermediate can occur during uncatalysed heating; the first chemical equation gives the final overall balance. The second represents the familiar nitrous oxide pathway, with hot water initially as vapour. It does not mean that ammonium nitrate has only one decomposition pathway: conditions, impurities and confinement can produce different gases and violent decomposition.^[ref]

The third is calcination of limestone to quicklime. Its extent depends on temperature and the partial pressure of carbon dioxide; removing carbon dioxide favours further decomposition. Reversing the process gives carbonation of calcium oxide.

For dissolution in hydrochloric acid, the corresponding balances areand“Magnesia” here means magnesium oxide, and “alumina” means aluminium oxide. Zinc undergoes an oxidation-reduction reaction, reducing hydrogen ions to molecular hydrogen. The oxides instead undergo acid-base reactions: hydrogen ions convert oxide into water, without hydrogen evolution. The chlorides are dissolved species in water, rather than anhydrous molecular salts necessarily existing intact in the solution. Strongly ignited aluminium oxide may dissolve slowly; the balance does not determine the rate.

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.

Calcium hydroxide prepared by hydrating calcium oxide.