Chlorine is a deadly poison gas employed on European battlefields in World War I. Sodium is a corrosive metal which burns upon contact with water. Together they make a placid and unpoisonous material, table salt. Why each of these substances has the properties it does is a subject called chemistry.

From common salt are obtained chemically as primary derivatives chlorine—both a war gas and a means of purifying water; and 'caustic soda.' … [O]n the chlorine side there is obtained chloride of lime, (a bleaching powder and a disinfectant), chloroform (an anesthetic), phosgene (a frightful ware gas), chloroacetophenone (another war gas), and an indigo and a yellow dye. [O]n the soda side we get metallic sodium, from which are derived sodium cyanide (a disinfectant), two medicines with [long] names, another war gas, and a beautiful violet dye. Thus, from a healthful, preservative condiment come things useful and hurtful—according to the intent or purpose.

In August, 1896, I exposed the sodium flame to large magnetic forces by placing it between the poles of a strong electromagnet. Again I studied the radiation of the flame by means of Rowland's mirror, the observations being made in the direction perpendicular to the lines of force. Each line, which in the absence of the effect of the magnetic forces was very sharply defined, was now broadened. This indicated that not only the original oscillations, but also others with greater and again others with smaller periods of oscillation were being radiated by the flame. The change was however very small. In an easily produced magnetic field it corresponded to a thirtieth of the distance between the two sodium lines, say two tenths of an Angstrom, a unit of measure whose name will always recall to physicists the meritorious work done by the father of my esteemed colleague.

One of the many useful properties of giant nerve fibres is that samples of protoplasm or axoplasm as it is usually called can be obtained by squeezing out the contents from a cut end ... As in many other cells there is a high concentration of potassium ions and relatively low concentration of sodium and chloride ions. This is the reverse of the situation in the animals' blood or in sea water, where sodium and chloride are the dominant ions and potassium is relatively dilute.

Sir Humphrey [sic] Davy
Abominated gravy.
He lived in the odium
Of having discovered sodium.
Said to have been written as a schoolboy during a chemistry class at St. Paul's School. [An example of a clerihew, an irregular form of biographical humorous verse, devised by the author.]

[Davy's] March of Glory, which he has run for the last six weeks—within which time by the aid and application of his own great discovery, of the identity of electricity and chemical attractions, he has placed all the elements and all their inanimate combinations in the power of man; having decomposed both the Alkalies, and three of the Earths, discovered as the base of the Alkalies a new metal... Davy supposes there is only one power in the world of the senses; which in particles acts as chemical attractions, in specific masses as electricity, & on matter in general, as planetary Gravitation... when this has been proved, it will then only remain to resolve this into some Law of vital Intellect—and all human knowledge will be Science and Metaphysics the only Science.
In November 1807 Davy gave his famous Second Bakerian Lecture at the Royal Society, in which he used Voltaic batteries to 'decompose, isolate and name' several new chemical elements, notably sodium and potassium.

[Professor Bragg asserts that] In sodium chloride there appear to be no molecules represented by NaCl. The equality in number of sodium and chlorine atoms is arrived at by a chess-board pattern of these atoms; it is a result of geometry and not of a pairing- off of the atoms.