Guide to a Course of Quantitative Chemical Analysis; Especially of Minerals and Furnace Products, Illustrated by Examples (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1872 edition. Excerpt: ... repeat the operation, after the weight has been determined, in order to be certain that the ignition the first time had not been stopped too soon, which is known by the fact that the weights in both cases remain the same. The direct determination of carbonic acid, in general, is seldom undertaken, and especially is this the case with those carbonates, whose bases suffer some change when ignited in the air. When such a determination has to be made, the ignition must be performed in some other indifferent gas, for instance, in carbonic acid itself and not in air. If the carbonate, whose acid is to be determined by ignition, contains also water, it is ignited in a small glass retort or some other similar apparatus, attached to a receiver containing chloride of calcium. 2. Estimation of the carbonic acid by another acid. Since the stronger acids liberate carbonic acid from all its combinations in the form of gas, they are had recourse to in all those cases in which the ignition of the substance is not applicable. This method is two-fold: either the volume of the evolved gaseous acid is determined over mercury in a graduated tube; or the loss of weight of the apparatus, which is caused by the evolution of the gas, is ascertained. The first method is not so frequently used, because it presupposes that the mercurial. apparatus is always at hand, and especially a practical experience in analytical investigations with gases. The second method is the one in general use. Although in principle it is exceedingly simple, yet certain precautions must be taken, especially such as aim to prevent the escape, along with the carbonic acid, either of water or of a part of the acid employed in producing the decomposition in the form of vapor. On this account the...