Hydrogen
2 of the 7 encyclopedias on this shelf carry an entry for Hydrogen. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
hi'dro-jen, an element in the form of a gas, discovered in 1766 by Cavendish. It is without color, smell, or taste. It is not poisonous. Hydrogen is the lightest substance known. A balloon filled with hydrogen and set free will be forced upward with a bound by the heavier surrounding air. The weight of hydrogen is taken as a standard for gases. Thus we say the weight of hydrogen is 1 and that of oxygen 16. It may be burned in air, producing water. Hydrogen is difficult to confine. It passes through a stone jar or a brick or an ordinary plastered wall. In 1878 it was liquefied and frozen free, that is to say, uncombined. Hydrogen occurs in enormous quantities in the sun. It is found free in the openings of volcanoes and in certain salt mines and gas wells. It usually occurs in combination with other elements. It forms a trifle over one-ninth of water by weight. In addition to its presence as part of moisture, hydrogen enters into the tissues of all animal and plant life. See Oxygen ; Water ; Gas
Collier's New Encyclopedia (1921)
a monatomic metallic element, which exists in the state of gas. Symbol H; at. wt., 1; density, 0.06927; air being 1; weight of a liter of hydrogen, 0.0896 grammes, called a crith. Hydrogen can be obtained by the electrolysis of water, H₂O, the H being liberated at the platinum pole; by the action of metallic sodium and water; also by passing steam over iron filings, 3Fe + 4HOH = Fe3O4 +8H'; by boiling zinc with caustic potash, 2KHO + Zn = K. ZnO2 +2H'; but H is generally made by the action of dilute H2SO4 on zinc. Hydrogen can be purified by passing it through a solution of two parts of K2Cr2O7 in 20 parts of water and one part of H2SO4, then washing it with KHO, and drying it by passing it through concentrated H2SO4.