Hydrogen Dioxide
hydrogen peroxide, H₂O2, or HO - OH. Obtained by the action of dilute sulphuric acid and barium peroxide, BaO2.
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Single-source entries: H (95)
These 17 listings are so strange that each appears in only one of the 7 encyclopedias we compared. They include such classics as Hydrogen Dioxide, Hydrogen Peroxide, Hydrogen Sulphide.
Hydrogen Peroxide
a compound of hydrogen and oxygen, containing a larger proportion of oxygen than water, ater, the other compound of these elements.
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Hydrogen Sulphide
H2S, sulphide of hydrogen, hydric sulphide, sulphydric acid, hydrosulphuric acid, sulphuretted hydrogen. A gas obtained by passing hydrogen through sulphur, or by burning sulphur vapor in hydrogen.
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Hydrography
a branch of science which deals with the measurement and description of the seas, lakes, rivers, and other waters, as used for purposes of commerce or navigation; the art of marine surveying and of the construction of charts.
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Hydroida
in ZOology, a typical sub-class of Hydrozoa. They have an alimentary region or polypite provided with an adherent disk or hydrorhiza and prehensile tentacles. Unlike hydra, the type of the sub-class, most of the hydroida live in societies, each of which constitutes a polypidom so like a seaweed that it is often collected as such. But while the apertures on an ordinary seaweed are only minute pores, the Hydroida have little cup-like cells along the stem and at the extremities of the branches, in which the individual polyp lives. The cells have a small hole at the bottom, and the stock is hollow, so as to enable the individual polyps to remain part of a compound organism. The sub-class is divided into five orders, Hydrida, Corynida, Sertularida, Campanularida, and Thecomeduse. The Polyzoa or Bryozoa, once ranked with the sub-class, now figure as a distinct class, arranged under the subkingdom Molluscoida. See HYDROZOON.
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Hydrokinetics
that branch of hydrodynamics which treats of the application of forces producing motion in fluids, having thus to do with the flow of liquids in pipes, its issue from orifices under certain pressures, etc.
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Hydromechanics
a term sometimes used to include hydrodynamics and hydrostatics, as also hydraulics, or the department of engineering which deals with the application of liquids in motion to machinery. Hydromechanics is sometimes limited to the latter department alone. On the other hand, hydraulics is sometimes made to cover hydrodynamics.
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Hydrometer
an instrument for determining the relative densities of liquids. Distilled water is usually referred to as the standard of comparison. It consists essentially of a bulb or float weighted at bottom so as to float upright, and having an elongated stem, graduated to indicate the density of the liquid by the depth to which it sinks.
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Hydroscope
an instrument for measuring the dampness or moisture of the air or of any other gas.
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Hydrostatic Press
a machine in which the pressure applied to a small piston is by means of water transmitted to a larger one; great pressure is thus produced, the increase being in the proportion of the excess of the sectional area of the one piston over the other. In application the different parts of a hydrostatic press occupy every possible position with regard to each other, and in many the force pump is worked by hand. Great force, with slow motion, is communicated to a piston by means of water forced into the large cylinder in which it moves, by a forcing pump of small diameter, to which the power is applied, the principle involved being the same as in the hydrostatic bellows.
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Hydrostatics
a department of science which treats of the conditions of equilibrium in liquids. For a liquid to remain at rest in any vessel, first, its surface must be everywhere at right angles to the forces which act on the molecules of the liquid, and, second, every molecule of the mass of the liquid must be subject in every direction to equal and contrary pressure. If the same liquid be placed in several vessels freely communicating with each other, it will stand in them all at the same horizontal level. If two or more liquids be placed in the same vessel they will arrange themselves according to their relative densities, after which the equilibrium will be stable. According to Hallam, the real creators of the science were Castellio (1577-1644), and Torricelli (1608-1647).
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Hydrosulphuric Acid
or sulphuretted hydrogen or hydrothionic acid (H2S), is a colorless inflammable gas produced by the putrefaction of sulphurous organic matters. Many mineral waters contain it naturally. It may be artificially produced by burning sulphur vapor in hydrogen, or by passing hydrogen through sulphur. It has a sweet taste but a very nauseous odor as of rotten eggs. It has poisonous effects when breathed, and experiments have shown that birds perished in air which contained 1/1500th part of the gas.
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Hydrothorax
a name given to serous fluid occupying the pleura. It may take place as the result of inflammation, also in heart disease, in disease of the kidneys, and sometimes in anæmia. HYÈRES (ē-ār') a small town of France, 3 miles from the Mediterranean. It is celebrated for the beauty of the situation and the mildness of the climate, and is therefore much resorted to by foreigners suffering from consumption or nervous complaints.
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Hygeia
The goddess of health, daughter of Aesculapius . She was held in great veneration among the ancients. Hymenaeus or Hymen. The god of marriage among the Greeks, was the son of Bacchus and Venus , or, according to some, of Apollo and one of the Muses. 2026 Editor's Note: In Greek mythology, Hygeia is the personification of health and cleanliness, and her name serves as the etymological root for the modern word " hygiene ." She is typically identified as the daughter of Asclepius (Aesculapius) and is one of five sisters who each represent a specific facet of the healing arts, including Panacea (universal remedy) and Iaso (recuperation). (Ed: BR 2026-07-02)
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Hygieia
hi-ji-e'ya, or Hygeia, hi-je'-ya, in Greek mythology, the goddess of health. She was the daughter of Aesculapius, according to some accounts, while others make her his wife. In works of art she appears in a long robe, and is employed in feeding a serpent from a cup.
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Hygiene
the study of the prevention of disease, the art of preserving health, through wise sanitary precautions, such as attention to diet, regimen, etc.
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Hygrometer
an instrument for measuring the comparative moisture of the air. There are three kinds: (1) those which act by absorption; (2) by condensation, and (3) those in which the hygrometric condition is deduced from observations of a wet and dry bulb. Of the first class is the hygrometer of Saussure (died 1799). It consists a human hair boiled in ly lye, and acts by absorption and evaporation, lengthening or contracting as the air is more or less moist.
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