. The principles of chemistry . the liquid: this gives a vapour which displaces the air, and fills the sphe-rical space. When the air and vapour cease escaping from the sphere, it is fused up orclosed by some means; and when cool, the weight of the vapour remaining in the sphereis determined (either by direct weighing of the vessel with the vapour and introducingthe necessary corrections for the weight of the air and of the vapour itself, or theweight of the volatilised substance is determined by chemical methods), and the volumeof the vapour at t and the barometric pressure 7/ are then calcul
. The principles of chemistry . the liquid: this gives a vapour which displaces the air, and fills the sphe-rical space. When the air and vapour cease escaping from the sphere, it is fused up orclosed by some means; and when cool, the weight of the vapour remaining in the sphereis determined (either by direct weighing of the vessel with the vapour and introducingthe necessary corrections for the weight of the air and of the vapour itself, or theweight of the volatilised substance is determined by chemical methods), and the volumeof the vapour at t and the barometric pressure 7/ are then calculated. The volumetric method {h) originally employed byGay-Lussac and then modified byHofmann and others is based on the principle that a weighed quantity of the liquid tobe experimented with (placed in a small closed vessel, which is sometimes fused up before MOLECULES AND ATOMS 30B tion of definite chemical compounds, shows that the volumes of the react-ing substances in a gaseous or vaporous state are either equal or are in n. Fm. 54.—Hofmaiins apparatus foi-(letermiiiiiig vapour densities. Tlieinternal tube, about one metre long-,which is caUbratfd aud graduated,is filled with mercury aud invertedin a mercury bath. A. small bottle(depicted in its natural size on theleft) containing a weighed quantityof the liquid whose vapour density isto be determined, is introduced intothe Torricellian vacuum. Steam,or the vapour of amyl alcohol, &c.,is passed through the outer tube,and heats the internal tube to thetemperatiu-e t, at wliich the volumeof vapour is measured.
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