A cyclopaedia of physical sciences : comprising acoustics, astronomy, dynamics, electricity, heat, hydrodynamics, magnetism, philosophy of mathematics, meteorology, optics, pneumatics, statics &c. &c / by J.P. Nichol with the assistance of eminent scientific men.

John Pringle Nichol

Date:: 1860

Credit: A cyclopaedia of physical sciences : comprising acoustics, astronomy, dynamics, electricity, heat, hydrodynamics, magnetism, philosophy of mathematics, meteorology, optics, pneumatics, statics &c. &c / by J.P. Nichol with the assistance of eminent scientific men. Source: Wellcome Collection.

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$gases, whose coefficients of absorption are respec- tively a, a', a, &c. If V, v', v, represent tho proportions of each gas in the mixture, it can be shown that a v, a'v', a v, &c., are tlie measures of the volumes of the different gases absorbed by the liquid under any given pressure; and, con- sequently, that in a unit-volume of the com- pound gas absorbed, the following quantities of the several gases will be found, viz.:— a V a'v' aV-i-a'vf + av+ aV + a! v' + a (2.) Secondly, If the superposed atmosphere be limited, the pressure will change as absorption proceeds, and the problem becomes somewhat more complex. Suppose that the atmosphere at first, under the pressure P, contained v and v' volumes of two gases, whose coefficients of absorp- tion at zero temperature are a and a', and let X and x' designate the unknown final pressures of the two elastic fluids. The volumes absorbed, reduced to the pressure P, will evidently b& V'' + ' U ax and At first, one of the gases under the pressure P occupied a volume equal to v. There remains then unabsorbed a quantity capable of occupying, under the same pressure, a volume expressed by V — ; and as this gas really occupies a volume V + v' under the pressure x, we derive from the law of Mariotte the equation u ax (v + vf)x , V ^ = p i whence, _ vV V + v' + u a The quantity of this gas not absorbed, there- fore, is V + v' V ' . V + V' + U a And so of the other gas, or of any element of a more complex combination.—(3.) Buusen next ex- amines the effect of the variation of temperature, and, after elaborate investigation, he constructs a table, of which the following is an extract. It gives the coefficient of absorption of the gases by water under pressure 30 inches, and at any tem- perature i, Centigrade:— Nitrogen, c = 0,020346 — 0,00053887 i + 0,000011156 i« Hydrogen, c = 0,0193 Ethyle gas, c = 0,031474 — 0,0010449 t + 0,000015066 Gas from a marsh, c = 0,05449 — 0,0011807 t + 0,000010278 f Methyle gas, c = 0,0871 — 0,0033242 t + 0,0000603 f Carbonic oxide, c = 0,032874 — 0,00081682 t + 0,000016421 f Olefiantgas, c = 0,25629 — 0,00913631 t + 0,000188108 f Carbonic acid gas, c = 1,7967 — 0,07761 < + 0,0016424 f After exposing the theory of the subject in the general manner indicated above, Bunsen proceeds 10 develop certain valuable applications of his formula. Referring for his processes — which are exceedinglj' simple—to his second memoir, in the Philosophical Magazine for 1855, vol. i., we shall here make room for the more important of his results.—(a), Supposing that in the case of a mixed gas, the following quantities are known, viz.:—a, the absorption-coefficient of the first gas; ^, the absorption-coefficient of the second; V the common volume of both gases before absorption under pressure P; the residual volume after the absorption under pressure Fj ; and, lastly, the volume A of the absorbing water: then if two gases, reduced to pressure 1, may be deter- mined. In the memoir referred to, the formula is tried on two unknown mixtures of hj'drogen and carbonic acid gas; and for the sake of com- parison, the same gas was analyzed by the ordi- nary endiometric methods. The following are the results: The first experiment gave— 1. By endiometry, . '2. By absorptiometry, Hydrogen. 0'9246 0-9207 Carbonic Acid. 0-0754 0 0793 we have and W = VP A = (Vi + a, 7i) Px + H A) Pi « + 2/ W — B A A — B ' \V A_W B x+y A —B W from which x and y, the original volumes of the By the second experiment on other proportions of the same gases, Bunsen obtained— 1. By endiometry, 2. By absorptiometry. Hydrogen. 26-8L 2G-67 Carbonic Acid. 73-19 73 33 The correspondence in both cases is certainly suf- ficiently remarkable to establish the value of absorptiometry (b), But this mode of analysis may go much farther; it may determine also the nature of the component parts of an unknown gas, as well as their proportions in the compound, when once the absorption-coefficients of all the gases are determined. Bunsen justly remarks that any general re-agent, to distinguish between the con- stituents of a gaseous mixture, has hitherto been wanting. The quantitative composition of a gas$