A series of chemical problems with key for use in colleges and schools / by T.E. Thorpe. Rev. and enl. by W. Tate ; with a preface by H.E. Roscoe.

  • Thorpe, T. E. (Thomas Edward), 1845-1925.
Date:
1891
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Licence: Public Domain Mark

Credit: A series of chemical problems with key for use in colleges and schools / by T.E. Thorpe. Rev. and enl. by W. Tate ; with a preface by H.E. Roscoe. Source: Wellcome Collection.

    45/160 (page 33)
    .atmosphere. Barometer height, 754'8 mm. V'olume of fglobe, 250 c.c. Residual air, 245 c.c. at io'3 mm. and ii7'2°C. Excess of weight of globe, o‘8765 gram. Weight (of air displaced 0 3020 gram. AVOGADRO’S HYPOTHESIS ; DENSITY AND MOLECULAR WEIGHT; VALENCY, EQUI- VALENTS AND ATOMIC WEIGHTS. According to Avogadro's Hypothesis equal volumes (of gases, at the same temperature and pressure, contain tthe same number of molecules. Hence it follows that the molecular weights of bodies in tthe state of gas or vapour are in the same ratio as their ‘specific gravities or vapour densities : e.g. if H = i, the ‘sp. gr. of gaseous HCl. = i8'i8. Assuming the molecular weight of H to be 2, the -molecular weight of HCl is 36'36. The molecular weight of a gaseous element or compound :may be thus defined : The molecular weight of a gaseous ‘element or compound is a number which expresses how :many times greater than two unit masses of hydrogen is tthe mass of the specified element or compound which occupies (under the same conditions of temperature and :pressure) the same volume as is occupied by these two ■unit masses of hydrogen. The niaxiuitim atomic weight of an element is a number which expresses how many ttimes greater is the smallest mass of that element which ccombines with other elements to form a compound gaseous :Tnolecule, than the smallest mass of hydrogen which com- bines with other elements to produce a compound gaseous molecule, such smallest mass of hydrogen being taken as unity. (Watts’s I. p. 341.) That property of an atom which determines the number cof other atoms with which it can combine to form a com- pound molecule is termed its valency or atomic value. Valency is usually expressed as the number of hydrogen iatoms, or atoms chemically equivalent to hydrogen, which one atom of the specified element can combine with or 'replace when in the same state as in the compound considered. D