Text-book of medical and pharmaceutical chemistry . d.—By the decomposition of the mineral acids with somemetal, as zinc, iron, or magnesium. In this case, the metal takesthe place of hydrogen, which is crowded out of the acid mole-cule. Zn + H^SO, = ZnSOi + H^ 65 grams of zinc give 2 grams = litres of hydrogen. HYDROGEN. 109 Water is added to dissolve the zinc sulphate formed, and toprevent it from crystallizing on the surface of the zinc. Chemi-cally pure zinc, however, will not dissolve in very dilute acid,unless it be made one pole of a galvanic couple. This method is the one usually
Text-book of medical and pharmaceutical chemistry . d.—By the decomposition of the mineral acids with somemetal, as zinc, iron, or magnesium. In this case, the metal takesthe place of hydrogen, which is crowded out of the acid mole-cule. Zn + H^SO, = ZnSOi + H^ 65 grams of zinc give 2 grams = litres of hydrogen. HYDROGEN. 109 Water is added to dissolve the zinc sulphate formed, and toprevent it from crystallizing on the surface of the zinc. Chemi-cally pure zinc, however, will not dissolve in very dilute acid,unless it be made one pole of a galvanic couple. This method is the one usually employed for the preparation ofhydrogen in the laboratory. The apparatus is shown in gas prepared from commercial zinc and acid is not pure, how-ever, as it contains other gases derived from impurities in the ma-terials used. Pure hydrogen in small quantities, may be preparedby the first method, or by decomposing water with an alloy ofsodium and mercury—sodium amalgam. log. Properties.—When pure, at ordinary temperatures Fig. PREPARATION OF HYDROGEN. and pressures, hydrogen is a colorless, transparent, odorless,tasteless gas. It is 14I/2 times lighter than air, being the lightestgas known. One liter of it at 0° C. and 760 mm. pressure, weighs .0896grm, =: the crith. It is almost insoluble in alcohol, and at atemperature of —140^ C. and under a pressure of 650 atmos-pheres, it has been condensed to a steel-blue liquid. It is thebest conductor of electricity and heat among the gases. It isvery diffusible, and a vessel to contain it, must be made of glassor some very compact material. Certain metals absorb largequantities of it. Palladium will absorb 900 times its volume of MEDICAL CHEMISTRY, Fig the gas : spongy platinum, sodium, potassium and iron alsoabsorb considerable quantities of it. This action of the metalsis called occlusion. During the condensation of the gas in thepores of the metal, the latter is heated to a considerable jet of hydro
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