Zinc sulfide is $\mathrm{ZnS}$, a semiconductor compound with common cubic and hexagonal structural forms. Sphalerite is the familiar cubic mineral form.

Its optical response depends on crystal structure, defects, and dopants. Zinc sulfide therefore illustrates why luminescence is often a property of a carefully prepared material rather than a prediction from the bare formula alone.

A silver halide is a compound of silver with a halogen, commonly represented as AgX for a monovalent halide. Silver bromide, silver chloride, and silver iodide are important examples.

Several silver halides are photosensitive. Light-generated charge can initiate formation of tiny silver-rich centres in a photographic grain, and chemical development amplifies the latent change into a visible image. This connects a microscopic photochemical event with macroscopic image formation.

An oxide is a compound in which oxygen is combined with another element, usually with oxygen formally in oxidation state $-2$. Ionic metal oxides and covalent nonmetal oxides can have very different structures.

For example, magnesium oxide is a lattice solid, whereas carbon dioxide is molecular. Peroxides contain an oxygen-oxygen unit with a different oxidation-state assignment, so they should not be treated as ordinary oxides merely because they contain oxygen.

Cadmium chloride is conventionally written $\mathrm{CdC}{\mathrm{l}}_2$, with cadmium in oxidation state +2. Solid and hydrated forms must be distinguished from dissolved cadmium-chloride species.

In chemical solution, chloride concentration can change the coordination environment around cadmium. A bulk formula therefore specifies overall composition without uniquely specifying every molecular or ionic species present.

Tetrachloroethylene is $\mathrm{C}{\mathrm{l}}_2\mathrm{C}=\mathrm{CC}{\mathrm{l}}_2$, a chlorinated molecular liquid. Its four chlorine atoms supply a large chlorine inventory per molecule.

In the Homestake experiment, tetrachloroethylene served as a target for detecting solar neutrinos through a rare chlorine-to-argon nuclear transformation. The solvent's chemical identity determines the target inventory, while the observed conversion is a nuclear process.

Gallium arsenide is the binary semiconductor $\mathrm{GaAs}$, containing one gallium atom per arsenic atom in its ideal composition. Its common zinc-blende-related structure is distinct from a simple mixture of elemental gallium and arsenic.

Its direct band gap supports optical transitions useful in emitters and photodetectors. Crystal defects, doping, and interfaces affect device behaviour in addition to the bulk chemical formula.

Gadolinium sulfate octahydrate is the hydrated salt $\mathrm{G}{\mathrm{d}}_2(\mathrm{S}{\mathrm{O}}_4{)}_3\cdot 8{\mathrm{H}}_2\mathrm{O}$. Gadolinium(III) ions provide localized magnetic moments, while water of crystallization is part of the crystal composition.

The material was used in the Giauque-MacDougall magnetic cooling experiment. Changing the magnetic field under suitable thermal isolation changes the spin entropy and the temperature, connecting the salt's microscopic magnetic states with refrigeration.

Gadolinium antimonide is the binary compound $\mathrm{GdSb}$, with a rock-salt-related crystal structure. Its low-temperature antiferromagnetism and electronic transport make it useful for studying the relation between magnetic order and electronic bands.

Epitaxial thin films allow strain and thickness to be varied while measuring transport or photoemission. This separates changes caused by the host composition from those produced by its crystalline environment.^[ref]

The compound $\mathrm{AlC}{\mathrm{l}}_3$. In an ideal fully dissociated aqueous-electrolyte bookkeeping model, formula concentration $c$ supplies $c$ of triply charged aluminium ions and $3c$ of singly charged chloride ions, giving ionic strength $I=6c$. Hydrolysis, ion association and nonideal activities can make this simple model inadequate for concentrated real solutions.

Laboratory protocol in Chem2O06 Laboratory Manual by McMaster University. No individual author byline is established. The footer is dated 17 September 1997; the manual identifies the 1997/98 course edition.

Online text: www.chemistry.mcmaster.ca/~chem2o6/labmanual/expt3/exp3-p.html

Cited section: Part A: 25 mL cyclohexane plus 25 mL p-xylene; top of thermometer bulb midway in opening to condenser; Part A: heating mantle on ring clamp, clay boiling chip, roughly one drop per second; Part A and B: record head temperature every 2 mL until 45 mL collected; Part B: 100 mL round-bottom flask and fractionating column; proceed as above; Recording of Results: paired temperature-volume plots, no azeotrope for this pair, volume is not composition; Experimental Notes item 2 mentions condenser water flow; no inlet/outlet direction established.

Introduction in Chem2O06 Laboratory Manual by McMaster University. The page heading says Experiment 2, while the manual index and directory identify Experiment 3. The footer is dated 17 September 1997; its initials do not establish a personal author.

Online text: www.chemistry.mcmaster.ca/~chem2o6/labmanual/expt3/exp3-int.html

Cited section: General Principles and boiling-point discussion; A Mixture of Ideal Liquids: first/later fractions; Liquids that Form Azeotropes: equal-composition constant-boiling mixtures and separation boundaries; Fractional Distillation: packed column and nonideal efficiency.

Cell counting estimates the number of biological cells in a preparation. A count per calibrated volume gives number density; multiplying by the whole preparation's volume estimates its total count. A trypan blue exclusion test adds an operational distinction between dye-excluding and dye-stained biological cells.

For positive recoverable counts $N_0,N_1$ bracketing one growth interval, define its net cell line population doublings byThe formula counts how many factors of two produce the observed net factor. For exactly two divisions per original biological cell, with all daughters recovered, $N_1=2^2{N}_0$, giving $d=2$. Death or loss of biological cells makes this a net estimate of division.^[ref]

Under constant-rate exponential growth, $N(t)=N_0{e}^{rt}$, a growth interval of duration $\Delta t$ givesFor the constructed fourfold increase over $48\mathrm{h}$, $d=2$ and the model doubling time is $24\mathrm{h}$. The proof follows by taking the natural logarithm and solving $e^{r{t}_2}=2$. This is a fitted property of that interval and model: it is not a universal HeLa doubling time, nor the interval between two divisions of each individual biological cell. Across successive growth intervals, add their $d$ values; keep transfer losses separate as in cell culture passage accounting.

A subculture transfers part of a cell culture into fresh cell culture medium; each transfer adds one passage.^[ref]

An immortalised cell line can apparently sustain unlimited cell line population doublings under suitable conditions. Immortality describes lineage reproduction, not individual biological cell survival.^[ref]

An autoclave uses heated, pressurized water vapor to sterilize suitable materials, including equipment for cell culture.

A cell culture medium supplies a cell culture's nutrients and chemical environment.^[ref]