Hydrogen, in the proportion of half the volume of the air used, must now be passed into I, and from thence into F, when the volume Of the mixed gases must be again de as before. An electric spark must now be passed through the mixed gases in F by Means of the platinum wires at m. ' A slight explosion occurs, after which we observe' a considerable contraction in the volume of the mixed gases. The determination of this contraction terminates the analysis. One third of the contraction thus determined represents the volume of oxygen contained in the air submitted to analysis, and in this case, as oxygen and nitrogen were the only gases present, the estimation of the former also determines the latter. Such an analysis as that which we have described is tefmed a direct determination; in other cases, we employ an indirect method.
1. The method of direct determination is applicable to mixtures of the following gases: carbonic acid, oxygen, olefiant gas, and carbonic oxide. If all these gases are present in the specimen to be analyzed, a few drops of a concentrated solution of potash is introduced into the apparatus„ measured quantity 9f the gas has-been transferred to it as before; the carbonic acid is speedily absorbed by the potash, and converted into carbonate of potash. The remaining gas is remeasured at'the same pressure as before, and the difference of the two measurements represents the volume of the carboniC acid that was present. The remaining gas is next brought into contact with a few drops of a strong solution of pyrogallic acid, which is introduced into the apparatus. In a few minutes, the whole of the oxygen is absorbed by the acid solution, which assumes a deep blood-red color. The remeasurement of the gas at the original pressure gives the volume of oxygen in the mixture.
The absorption of the olefiant gas is effected by the introduction into the tube I of a coke-bullet saturated with a solution of anhydrous sulphuric acid in oil of vitriol. This absorption occupies far more time than that of the preceding gas, an hour or more being required, and the residual gas contains Sulphuric acid and the vapor of anhydrous sul phuric acid, which must be removed by a few drops of a strong solution of potash. The residual gas being again measured in F, the diminished pressure represents the volume of olefiant gas. The qii-bonic oxide is then determined by a solution of dichloride of copper, which is best prepared by allowing a concentrated solution of the protochloride to be in contact with copper turnings in a stoppered bottle for some days. The gas must be brought in contact for ten minutes with a little of this solution, introduced into the apparatus. The pressure of the gas is again measured, and deter mines the volume of carbonic oxide that has been absorbed. This gas is, however,
usually determined by the indirect method. .
2. The method of indirect determination is especially applicable to mixtures of the following gases: hydrogen, light carbureted hydrogen, carbonic oxide, and nitrogen. We explode a known volume of the mixture of these gases in the tube an excess of oxygen, and determine (1) tlfe diminution of volume after the explosion, and (2) the volume of carbonic acid produced by the combustion. The gas that remains after the absorption of the carbonic acid (by a solution of potash), consists merely of nitrogen, with any excess of oxygen beyond what was necessary. The volume of oxygen deter mined by explosion with hydrogen, subtracted from the residual gas, gives the amount of nitrogen contained in the mixture.. For the determination of the respective volumes of nitrogen, hydrogen, carbonic oxide, and light carbureted hydrogen, we have the following data—viz. (1) the volume of the gas taken for analysis, which we will call A; (2), the volume of the- combustible gases contained in it, which we will call A', and is ascertained by deducting from A the amount of nitrogen determined as above; (3), the contraction of volume on explosion, which we will call C; and (4) the volume of carbonic acid generated on explosion, which we will call D; and we likewise know that on exploding one volume of hydrogen with an excess of oxygen, the contraction of volume is expressed by 1.5; that on similarly exploding one volume of carbonic oxide, the contraction is expressed by 0.5, while one volume of carbonic acid is produced; and that with light carbureted hydrogen the contraction is represented by 2.0, while one volume of carbonic acid is produced. Hence, if we call a', y, 2, the unknown volumes of nitrogen, hydrogen, carbonic oxide, and light carburetted hydrogen, we see at once that w=A—A', and x=A'—D-; and the above numerical data give us the equations.
C = + 22, and D = y ±z; whence y = 3A' — 2C + and z — +2C 2 2 3 8 which affords the complete solution of the analytical problem.
If, on the application of these formulm to the results of an analysis, one of the quan tities a', x, y, z is found = 0, or a small negative result, it obviously follows, that the gas whose volume is represented by the letter in question, is not present in the mixture.
For further details regarding this somewhat difficult branch of chemical analysis, we must refer to Bunsen's treatise, and to the articles "Analyze filr Gase," in the second edition of Liebig, Poggcndorff, and Wobler's Handw5rterbuch der Ohmic; arid " Gaso metric Analysis," in the English Cyc,lopcedia—Arts and Sciences, vol. iv.