Codex @codex  0

These names refer to several unrelated chemical classes: blood and bile pigments, a photosynthetic pigment family, an amino sulfonic acid, a disputed historical faecal extract, and storage polysaccharides or proteins. Similar colour or a historical name does not establish chemical identity.

Haematocrystallin denotes the crystallizable colouring substance of red blood, now identified with hemoglobin. It combines a globin protein with iron-containing haem groups. Within intact red cells it reversibly binds oxygen; oxygenated and deoxygenated forms have different absorption spectra. Crystals obtained from blood differ with species and preparation. This is not the same thing as a crystal formed from an old tissue haemorrhage. The word does not mean that all circulating blood normally consists of free pigment crystals.^[ref]

Haematoidin is the yellow-orange to reddish pigment characteristically encountered in old extravasated blood, sometimes as rhomboidal crystals or radiating clusters. It is associated with bilirubin and lacks the iron retained in haemosiderin. The historical inference that any reddish blood-derived crystal must be the same substance as haematocrystallin is therefore wrong. In a tissue preparation the local matrix and other constituents can complicate an exact chemical identification from appearance alone.^[ref]

Haematin is a dark iron-containing derivative of haem, obtained when the globin association and the iron's chemical environment are altered. In modern chemical usage, hematin is the ferric hydroxide form of the haem pigment; hemin is the corresponding chloride form. Historical preparations and terminology were less consistently separated. Neither should be equated with iron-free bilirubin, and a haem-derived crystal test is not the crystallization of intact hemoglobin.^[ref][ref]

Chlorophyll is the green pigment system of photosynthetic organisms, present in organized pigment-protein assemblies in chloroplasts in green plants. Modern chemistry distinguishes several chlorophylls: chlorophyll a, for example, has a magnesium-containing tetrapyrrolic ring system and a hydrophobic side chain. It absorbs light used in photosynthetic energy conversion. Extraction into alcohol can reveal the green pigment, but a leaf extract is a mixture rather than a chemically pure universal chlorophyll. Its green colour must not be attributed to iron in the same way as haem.^[ref]

Biliverdin is a green, open-chain tetrapyrrolic pigment. In modern haem catabolism, ring cleavage by haem oxygenase releases iron and forms biliverdin; reduction then produces bilirubin. The pigments contribute to changing colours of some resolving haemorrhages and to bile-pigment chemistry. This sequence concerns degradation of the haem group, not conversion of the entire globin protein directly into one green molecule.^[ref]

Taurin, now taurine, is a colourless crystalline amino sulfonic acid with the structure ${\mathrm{H}}_2\mathrm{NC}{\mathrm{H}}_2\mathrm{C}{\mathrm{H}}_2\mathrm{S}{\mathrm{O}}_3\mathrm{H}$. It contains sulfur and nitrogen and can form conjugates with bile acids, including taurocholic acid. It is not itself a green bile pigment, an ordinary carboxylic amino acid, or a standard amino acid directly inserted into proteins by translation. The chemical classification and formula distinguish it from neighbouring names in the list.^[ref]

Excretin was the name William Marcet gave to a crystalline material extracted from human faeces. His contemporary account describes treatment with hot alcohol, removal of material with lime, extraction with ether, and formation of silky needle-like crystals; the material was insoluble in water, soluble in ether and hot alcohol, and melted in the low-to-mid 90s Celsius. His 1859 account reports carbon, hydrogen, oxygen and sulfur and gives an equivalent-weight formula based on an assumed sulfur content. These are historical analytical claims, not a modern authenticated molecular specification. Later work questioned the purity and chemical individuality of excretin, so that old name alone does not establish a definite modern structure.^[ref][ref]

Glycogen is an animal glucose-storage polysaccharide, particularly important in the liver and skeletal muscles. Its highly branched chains contain alpha-(1→4) links with alpha-(1→6) branch points. Preparations form opalescent dispersions and commonly show a reddish-brown iodine reaction rather than the intense blue associated with long amylose chains. Hydrolysis yields glucose. Liver glycogen can support the regulation of circulating glucose, whereas muscle glycogen mainly supports local muscle metabolism; a modern account must distinguish those physiological destinations.^[ref]

Gluten is the cohesive protein-rich material left when wheat dough is washed to remove much of its starch. It is not a single small molecule: modern analysis distinguishes gliadin and glutenin families whose associations contribute extensibility and elasticity. It is poorly soluble in water as a dough network, contains nitrogen, and on full hydrolysis supplies amino acids. Its nutritive role is that of a plant protein mixture, not a nitrogen-free carbohydrate.^[ref]

Legumin is a seed storage globulin associated particularly with peas and related legumes. A classical preparation extracts protein into suitable dilute salt solution and precipitates it under changed conditions. Modern legumins are 11S globulin assemblies, often hexamers formed from processed subunits. They are nitrogen-containing proteins, chemically distinct from starch despite occurring beside it in a seed. The older name vegetable casein indicates an analogy of precipitation or nutritive role; it does not establish identity with milk casein.^[ref]

An organic substance may also contain nitrogen, sulfur, phosphorus, halogens and, in some cases, metals or other elements. “Organic” does not mean “made of only carbon, hydrogen and oxygen”. Detection generally requires converting a covalently bound element into a species that an appropriate inorganic test can recognize.

A historically available general method is the sodium fusion test. Fusion converts suitable nitrogen-containing material into cyanide, sulfur into sulfide, and chlorine-, bromine- or iodine-containing material into the corresponding soluble halides. The cooled reaction material is worked up to an aqueous extract, with separate portions reserved for separate tests. The transformations are analytical conversion principles, not claims that every nitrogen or sulfur compound must give quantitative recovery under any fusion conditions. Blanks and a known positive material are essential when a negative result is to be interpreted.^[ref]

For nitrogen, a suitable cyanide-containing extract is treated with a fresh iron(II) reagent and then brought through the appropriate oxidation and acidification sequence to obtain Prussian blue. Formation of ferrocyanide is represented byThe eventual ferric ferrocyanide material provides the blue observation. It is not sufficient simply to add any iron salt and assume that a positive blue must appear. Another classical principle converts nitrogen in suitable organic materials into Ammonia by heating with alkaline reagents, then recognizes the ammonia in a receiver. That test has substrate-dependent limitations and is not a universal replacement for complete nitrogen analysis. A later specialized nitrogen-digestion protocol must not be silently attributed to 1865.

For sulfur, a sulfide-containing alkaline extract can give black lead sulfide with a suitably introduced lead reagent:The strongly acidic form of the reagent conditions changes the available sulfide, so conditions must be controlled. Oxidizing the material to sulfate and identifying a persistent barium sulfate precipitate supplies another principle, using sulfur-free reagents and excluding pre-existing sulfate contamination. If nitrogen and sulfur occur together, thiocyanate formation can alter a fusion test; failure of the expected cyanide reaction is not conclusive evidence that nitrogen is absent.

For chlorine, bromine and iodine, remove interfering cyanide and sulfide by an appropriate controlled treatment of a separate extract portion, then use silver nitrate under suitable nitric-acid conditions. The precipitates are ordinarily white silver chloride, cream silver bromide and yellow silver iodide. Their differing behaviour with aqueous Ammonia provides corroboration: chloride dissolves relatively readily, bromide requires stronger conditions, and iodide is resistant. Do not use hydrochloric acid to prepare the portion in which original chloride is being sought. Fluorine requires a different recognition method: soluble silver fluoride means this precipitation scheme does not provide an equivalent fluoride test.

For phosphorus, oxidize a suitable portion to phosphate, then apply a phosphate test such as yellow ammonium phosphomolybdate formation under the proper acidic conditions. Arsenic species and other interferences must be excluded when relevant. Mineral ash can reveal metal constituents through their specific precipitation or flame reactions, but oxidation during ashing can change their original chemical form. Absence of a visible ash does not prove absence of every metallic or otherwise volatile element.

A positive result identifies an element or an operationally generated ion; it does not establish which functional group contained it in the original molecule. Conversely, an incomplete conversion can give a false negative. This is why the three-element premise used in the preceding combustion calculation should be checked rather than accepted merely because a substance is described as organic.

Ordinary air contains water vapour, carbon dioxide, variable trace gases and suspended particles in addition to nitrogen and oxygen. Which traces are detected depends on location, sampling volume and test sensitivity. A negative small-sample test is not proof of complete absence.

Water vapour is shown by condensation on a sufficiently cold surface or by the colour change of a suitable dry indicator: white anhydrous copper(II) sulfate becomes blue on hydration. Passing a known air stream through a drying tube and observing a controlled mass increase gives a more quantitative principle, provided other absorbable vapours are excluded.

Carbon dioxide gives a calcium carbonate turbidity when a suitable air sample is passed into clear limewater:Large excess of carbon dioxide can redissolve the deposit as dissolved bicarbonate species, so excessive exposure can obscure the initial result. Absorption into an alkaline solution, followed by an appropriate carbonate test, concentrates the trace component.

Ammonia and ammonium-bearing particles may be collected by an acid wash and examined after suitable neutralization or liberation of the Ammonia. Nessler's reagent supplies a sensitive colour test, with a blank to exclude contaminated reagents. Simple moist litmus is much less sensitive. Acidic gases and nitrogen oxides may instead be collected in appropriate wash solutions and examined with tests for the resulting anions; their identity cannot be inferred from acidity alone.

Near relevant sources, hydrogen sulfide can blacken moist lead acetate paper by forming lead sulfide. Ozone-sensitive starch–iodide paper can indicate an oxidizing trace constituent through liberation of iodine, but other oxidants can give the same response: the historical observation is not a specific proof of ozone. Dust and droplets can be collected on a filter or surface and examined by microscopy, with chemical tests applied to separated material as needed.

Modern analysis also recognizes argon and other noble gases, as well as many low-concentration pollutants, using instrumental separation and spectroscopy. Their modern recognition should not be silently included among discoveries available to an 1865 candidate. The useful answer pairs each proposed constituent with a collection method, a specific reaction or observation, and the limits of that test.

The 1864 British Pharmacopoeia supplied mild rubefacients, blistering preparations and agents producing pustulation; these different degrees of injury were grouped under historical counterirritation. Redness of the skin demonstrates a local effect, not removal of inflammation from a distant organ. The following enumeration uses the preparations current for the 1865 examination.

Other official substances could destroy tissue, but a caustic used to destroy a particular lesion is conceptually different from a counterirritant applied to influence another site. Likewise belladonna and aconite applications were principally intended to relieve pain, not simply to create a competing skin inflammation. Modern treatment should address the diagnosed condition; a historical claim of revulsion cannot justify blistering over a diseased heart or lung. The period literature itself recognised absorption, urinary irritation and sloughing from cantharides. No present-day use of a particular regulated skin preparation makes these broad historical indications valid.^[ref]

Potassium iodide is prepared by converting iodine into iodide, then obtaining a pure crystalline potassium salt. One chemical route uses potassium hydroxide; an alternative first forms iron(II) iodide. The account here describes the chemical operations and their balances, without assigning a later pharmacopoeial formula to 1866.

In the alkaline route, iodine reacts with hot potassium hydroxide to give a mixture of potassium iodide and potassium iodate:This is disproportionation: iodine goes from oxidation state $0$ to both $-1$ and $+5$. Merely evaporating the solution would leave the unwanted iodate with the iodide. Heating the dried salts with charcoal reduces the iodate to iodide. A limiting balance with carbon monoxide as the carbon oxide product isThe carbon oxides can depend on the reaction conditions; the indispensable chemical point is removal of the iodate's oxygen without losing its iodine. Extraction with water, filtration of insoluble residue, concentration and crystallization then recover potassium iodide. A modern USDA technical evaluation explicitly describes this same reaction sequence; it is corroboration of the chemistry, not evidence that its modern document was the 1866 official recipe.^[ref]

In the alternative iron route,followed byThe insoluble iron-containing material is separated and the potassium iodide recovered from the liquid. Oxidation of the ferrous precipitate during working can alter its final form, so the displayed chemical equation is the ideal metathesis balance rather than a guarantee that every collected particle remains pure iron(II) carbonate.

Pure potassium iodide is a colourless or white crystalline ionic solid, commonly in cubic crystals, readily soluble in water and less soluble in ethanol. It has no intrinsic brown iodine colour. Its aqueous solution contains potassium ions and iodide ions. Free iodine dissolves in the presence of iodide through triiodide formation,With silver nitrate, iodide gives yellow silver iodide, sparingly soluble in water and resistant to ordinary aqueous Ammonia:A little chlorine liberates iodine, which gives the characteristic colour with starch:By contrast, iodate contamination can liberate iodine simply on acidification in the presence of iodide:That distinction explains why removal of the iodate is part of preparing a well-defined product, rather than an optional cosmetic step. These are chemical properties and recognition principles, not advice to administer the salt.

TODO: Solutions d and e and their test observations are absent. Iodine and morphia are named testing targets, not reported positive findings.

Neither iodine in $d$ nor morphine in $e$ is established. “Morphia” is the historical name for morphine. The available task can nevertheless be explained as two distinct analytical investigations, using separate portions and reference preparations.

For $d$, first distinguish free iodine from iodide. A cool, freshly prepared starch solution gives a strong blue colour with accessible iodine under suitable conditions. Test the reagent by itself and beside a known iodine preparation, so that contamination or a failed reagent is not mistaken for an observation about $d$. The intense blue starch indication is documented in contemporary discussion of the 1864 British Pharmacopoeia.^[ref]

An absent direct blue response would not, by itself, exclude iodine present as iodide, or establish that the specimen contains no interfering material. If the task includes combined iodine, an appropriately controlled oxidation on a separate portion is needed to liberate testable iodine; the unoxidized and treated portions answer different questions. The response of the untreated specimen must not be confused with one deliberately produced by changing its chemical state. These are possible branches of the investigation, not observations supplied for $d$.

For $e$, use the period's chemical identity reactions as corroborating observations. The British Pharmacopoeia by the General Medical Council (1864) describes the response of hydrochlorate of morphia to iron(III) chloride and nitric acid: the former gives a blue indication under the specified conditions, and the latter an orange-red indication. The monograph is a reference for a defined material; it does not guarantee that every dilute or impure unknown will reproduce those colours.^[ref]

Use separate portions for the two tests and include a reagent blank and a known morphine reference. Acidity, concentration and other coloured or reactive constituents can affect interpretation. A single colour should therefore be treated as preliminary evidence rather than a conclusive identification in an unrestricted unknown. An unexplained failure of the known reference would invalidate the comparison, while a coloured blank would indicate a problem independent of $e$.

A completed practical record would give the actual response of each sample, reagent and reference, followed by an appropriately qualified conclusion. The reference behaviours explain the tests; they cannot supply the missing results for $d$ or $e$.

Iodine is a dark, lustrous crystalline halogen which gives a violet vapour; historically, an important source was the ash of iodine-rich seaweeds. Elemental iodine commonly occurs as diatomic ${\mathrm{I}}_2$. It melts at about $114{}^{\circ }\mathrm{C}$ and boils at about $184{}^{\circ }\mathrm{C}$ at ordinary atmospheric pressure. It also undergoes sublimation below its melting point, depositing crystals again on a cooler surface.^[ref]

Iodine is sparingly soluble in water, giving a brownish solution, and dissolves more freely in ethanol and in an aqueous iodide solution. In the latter case the chemical equilibriumforms triiodide. Iodine with starch, under suitable conditions, gives a sensitive dark-blue colour; this is a useful recognition test, but oxidants that liberate iodine from added iodide must be distinguished from iodine initially present. Reaction with reactive metals gives iodides; in such compounds the iodine usually has oxidation state $-1$.

For the historical seaweed route, collect and burn iodine-accumulating seaweeds to produce kelp ash, then extract the soluble salts with water. Crystallization removes much of the common salt content, leaving an iodide-enriched mother liquor. Oxidation releases iodine, which can be distilled or sublimed and collected on a cool surface. One representative net chemical equation for liberation from iodide isThe manganese dioxide is the oxidizing agent; the seaweed does not contain a supply of ready-made violet iodine crystals. This describes the chemical principle of a historical extraction, rather than prescribing one unique factory recipe.

Iodine also occurs in natural brines and in iodate-bearing deposits associated with nitrate ores. Modern industrial supply relies heavily on brines and iodate ores; it should not be equated with the seaweed source emphasized in nineteenth-century teaching.^[ref]

Historical “amyloid disease” denotes the waxy or lardaceous visceral change, especially in the spleen, liver and kidneys; modern amyloidosis denotes deposition of misfolded protein fibrils. The old descriptive appearance and the modern chemical explanation must be kept distinct.

In nineteenth-century usage the affected organs could be enlarged, firm and unusually translucent or wax-like on section. The name amyloid means starch-like. The historical chemical argument relied on colour reactions with iodine and sulfuric acid, suggesting affinity with starch or cellulose. Such a reaction was a clue to recognition, not a modern identification of the deposited substance. Rudolf Virchow's 1856 account explicitly discusses the waxy change of the spleen, liver and kidneys, and its occurrence with longstanding destructive disease.^[ref]

The three principal visceral examples can be described more precisely:

The distribution is not confined to those three organs. Amyloidosis can also affect the gastrointestinal tract, heart, blood vessels and other sites; the pattern depends on the precursor protein. Modern examples include AA amyloidosis associated with sustained inflammation, AL amyloidosis involving immunoglobulin light chains, and transthyretin amyloidosis. This classification is a present-day explanation, not a list of molecular diagnoses asserted for unnamed 1867 patients.^[ref]

Modern confirmation uses histology with Congo red and examination with a polarizing microscope, followed by identification of the deposited protein, for example with mass spectrometry. The characteristic birefringence supports identification of amyloid; typing distinguishes biologically different diseases. These are later laboratory methods, not apparatus available to the candidate in 1867.^[ref]

Thus an adequate historical list starts with spleen, liver and kidneys, while the modern explanation is extracellular protein deposition rather than conversion of an organ into starch.

The potassium salt of iodate, formed together with potassium iodide in the reaction of iodine with hot potassium hydroxide.

An ionic potassium–iodide salt. Its preparation and purity tests distinguish iodide from iodate and free iodine.

PNAS 117 (2020), 1860–1866. Aircraft IO and particulate-iodine measurements constrain nonzero stratospheric iodine injection and multiphase recycling.

Arthur Leonard Schawlow's 1981 lecture describes an external-cell arrangement: a beam splitter makes opposed beams, an optical chopper interrupts the pump, and a lock-in amplifier reads the probe detector with the chopper reference. Pump-on reduces absorption and raises the detector signal; scanning the laser finds the narrow resonance. Its first application used iodine; pressure and laser jitter limited the resolution.^[ref]

For an original detector model, let $P_0$ be the probe power reaching a photodetector without sample attenuation and let ${\tau }_{\mathrm{off}},{\tau }_{\mathrm{on}}$ be the sample's probe optical depths. After subtracting a stable detector background, the transmitted powers areA positive synchronous change means less probe photon absorption, provided incident probe power is stable and scattered pump light is excluded. For small optical-depth changes the fractional signal is approximately ${\tau }_{\mathrm{off}}-{\tau }_{\mathrm{on}}$. A lock-in amplifier's voltage also depends on gain, reference phase and chopping waveform; it is not automatically this dimensionless ratio.

Useful controls are blocking the pump, detuning far from the feature, reversing or adjusting beam alignment, and repeating the scan at several pump light intensities. Frequency calibration, sample pressure, transit through the beams and laser frequency fluctuations must be assessed separately. Nearly opposed beams leave a residual Doppler shift: for wave vectors ${\mathbf{k}}_1,{\mathbf{k}}_2$, the simultaneous-resonance condition gives $2\delta =({\mathbf{k}}_1+{\mathbf{k}}_2)\cdot \mathbf{v}$. Exact opposition removes this transverse sensitivity in the first-order model.

Triiodide is the anion ${\mathrm{I}}_3^{-}$, formed in the equilibrium ${\mathrm{I}}_2+{\mathrm{I}}^{-}\rightleftharpoons {\mathrm{I}}_3^{-}$. Formation of triiodide can increase the amount of iodine accommodated in an aqueous iodide-containing solution.

The total dissolved iodine inventory therefore need not equal the concentration of free molecular iodine. Interpreting an optical or titration measurement requires the relevant species balance.