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The three preparations use different chemistry: diethyl ether from ethanol by acid-catalysed dehydration, carbon disulfide by combination of carbon and sulfur, and chloroform by chlorination and cleavage of a suitable organic starting material. “Ether” here means diethyl ether, not every member of the modern ether class; “bisulphide of carbon” means carbon disulfide.

For diethyl ether, heating ethanol with a suitable proportion of sulfuric acid favours intermolecular dehydration:The historical explanation invokes formation of ethyl hydrogen sulfate and its reaction with a further ethanol molecule, regenerating sulfuric acid. The acid therefore need not be consumed stoichiometrically in the overall balance. The modern mechanism treats a protonated alcohol or related activated species as the substrate for attack by another ethanol molecule.^[ref] Conditions matter: excessive heating favours formation of Ethylene rather than ether, and strongly oxidizing conditions can give additional products. Condensation of the volatile product, removal of acidic and water-soluble impurities, drying and redistillation separate production from purification. A cold receiver is appropriate to the volatile ether; an open flame near the escaping vapour would be incompatible with its ready flammability.

For carbon disulfide, sulfur vapour is brought into contact with sufficiently hot charcoal in a retort:Here $\mathrm{S}$ records sulfur atoms in the balance, not a claim that the sulfur vapour has only monatomic molecules. The outgoing vapours are cooled and the liquid separated from excess sulfur and other impurities, then purified by distillation. The high-temperature reaction zone and the cooled collecting region have different functions. Carbon disulfide is a volatile, highly flammable solvent; its historical use does not establish harmlessness.^[ref]

For chloroform, a historically important route uses ethanol with a slurry containing bleaching powder. Oxidation first supplies acetaldehyde; further chlorination gives chloral, which alkali cleaves to chloroform and formate. An illustrative final step with calcium hydroxide isThe bleaching material supplies oxidizing and chlorinating capacity, while the alkaline conditions permit cleavage. It is misleading to describe the entire operation as one simple substitution directly replacing three hydrogens of intact ethanol. It is also unnecessary to pretend that commercial bleaching powder has a single invariant molecular composition.

Acetone supplies an alternative methyl-carbonyl starting material for the same broad haloform chemistry. In ionic notation a clean idealized balance isThe volatile product is condensed with water-containing material; a chloroform-rich phase is separated, washed appropriately, dried and redistilled. Identity and purity require more than observing a dense lower layer. These operations describe preparation chemistry rather than a specified pharmacopoeial recipe or a claim of suitability for anaesthesia. The historical anaesthetic importance of chloroform does not remove its toxic effects.^[ref]

For an 1866 discussion, distinguish conditions demanding special caution from a universal prohibition. Modern correction goes further: chloroform is not an acceptable routine surgical anaesthetic. Its toxicity cannot be removed by choosing an apparently healthy person.

The historical inquiry would examine the heart, lungs, general strength and the nature of the proposed procedure. A failing circulation, suspected serious myocardial degeneration, great exhaustion or blood loss, and severe respiratory impairment gave strong reasons to avoid or postpone a nonessential exposure. A full stomach, obstruction of the airway, difficulty maintaining breathing, or an operation threatening to contaminate the airway created additional hazards. Acute intoxication or other depressant drugs could complicate administration. The balance depended partly on whether the operation was essential and on what alternative method of relieving pain was available.

It would nevertheless be historically inaccurate to declare that the contemporary profession unanimously regarded all heart disease as an absolute contraindication. The 1864 committee's report said that heart disease in general did not automatically preclude surgical use, while specifically calling for care over fatty degeneration. It also discussed the difficulty of recognizing that condition during life. Its treatment of mouth and throat operations was likewise more qualified than a universal ban.^[ref] This is a record of the committee's judgement, not endorsement of its safety conclusion.

The delivery conditions also matter. An uncontrolled vapour concentration, failure to ensure air entry, lack of a dedicated competent observer, or inability to respond to loss of breathing and circulation makes an already hazardous intervention less defensible. Such circumstances concern how the drug is used rather than a disease-specific contraindication. The period distinction between direct circulatory failure and respiratory failure explains why watching only one sign was inadequate.^[ref]

Modern correction: chloroform can depress the central nervous system, disrupt cardiac function and cause delayed hepatic and renal injury. Its former use as an anaesthetic does not make it a current option. Modern anaesthetic assessment still considers cardiovascular and respiratory reserve, aspiration risk, other drugs and the proposed procedure, but uses contemporary agents, monitoring and trained personnel.^[ref][ref] In particular, absence of obvious heart disease is not evidence that a chloroform exposure is safe.