GAS, ANALYSIS OF. This department of analysis originated in the attempts of vari ous chemists, during the last quarter of the 18th, and the first quarter of the present century, to determine the volume of oxygen in specimens of atmospheric air taken from different localities. The general principle on which the early eudiometers (q.v.) were constructed, was that of exposing atmospheric air to the action of some substance which combined with its oxygen. Various eudiometers and eudiometrical processes were devised by Priestly, De Marte, Guyton, Seguin, Volta, Berthollet, Hope, Henry, Pepys, Eire, etc., which are now only of interest in an historical point of view. They were not only almost exclusively limited to the determination of the quantity of oxygen, but they were more or less imperfect in their action; and the analysis of the gases generally did not become developed into a system until prof; Bunsen of Heidelberg, some 80 years ago, began to devote himself•to the subject. Ingenkins instruments for the analysis of gaseous mixtures have recently been devised, not only by Bunsen, but by Regnault and Reiset,. Williamson and Russell, and Frankland and Ward. The instrument devised by the last-named gentlemen we shall presently describe; but before doing so, we must say a few words on the collection of gases for analysis. In collecting gases, we usually employ small glass vessels, the contents of which, consisting of water, mercury, or air, are displaced.by the gas to be analyzed. Of these three fluids, water is the least capable of general application, inasmuch as it gives rise to phenomena of absorption and diffu sion, which modify the composition of the gas that is to be collected, and gases are more or less soluble in it. For the best methods of collecting gases from mineral springs and waters, from volcanic lakes, geysers or boiling springs, from openings in rocks, clefts of glaciers, furnaces, fissures in volcanic craters, etc., we must refer to Bunsen's Gasometry, translated by Roscoe, 1857. Again, it must be recollected that the nature of the gas that is evolved often varies with the progressive phases of a decomposition, as, for example, iu the process of coking, or in the•phenomena of combustion and decomposition occurring in the strata of a furnace. In these cases, it is necessary to collect a series of specimens
during the progress of the decomposition.
Our limited space will not allow of our entering into the various details of the com plicated apparatus employed by Frankland and Ward, which is regarded as the best that has yet been invented. A full account of it may be found in their memoir in the Quarterly Journal of the Chemical Society, or in Williams's Handbook of Chemical Manipulation. The following remarks, which we take with slight modifications from their memoir, will, we trust, sufficiently explain the manner of using this apparatus. We take as an example an analysis of atmospheric air. A few (three or four) cubic inches of air, freed from carbonic acid, having been introduced into the tube I, it is trans ferred into F for measurement by opening the cocks /, 1', and placing the tube F in connection with the exit-pipe lb; the transference can be assisted, if necessary, by elevating the mercurial trough C. (The part marked b in the figure is merely the tubular well of the mercurial trough C.) When the air, followed by a few drops of mercury, has passed completely into F, the cock 1 is shut, and f turned, so as to connect F and 11 with h. Mercury is allowe.d to flow out until a vacuum of 2 or 3 in. in length is formed in H, and the metal in F is just below One of the graduated divisions; the cock f is then reversed, and mercury very gradually admitted from G, until the highest point in F exactly corresponds with one of the divisions upon that tube: we will assume it to be the sixth division, there being ten divisions in all. This adjustment of mercury, and the subsequent readings, can he very accurately made by means of a small horizontal telescope, placed at a distance of about 6ft., and sliding on a vertical rod. The height of the mer cury in H must now'be accurately determined; and if from the number thus read off, the height of the sixth division above the zero of the scale in H is deducted (the scale on H is not marked in the figure), the remainder will express the true volume of the gas, no corrections being required for variations of temperature, atmospheric pressure, tension of aqueous vapor, etc.