A system of instruction in quantitative chemical analysis / by C. Remigius Fresenius.
- Fresenius, C. Remigius, 1818-1897. Anleitung zur qualitativen chemischen Analyse. English
- Date:
- 1854
Licence: Public Domain Mark
Credit: A system of instruction in quantitative chemical analysis / by C. Remigius Fresenius. Source: Wellcome Collection.
61/680 page 41
![§ 18.] ESTIMATION OF WATER. the larger the amount of substance, the less harm can result from slight inaccuracies in weighing. For largish cjuantities of substance, the accuracy of weighing may be safely limited to within about one milligramme; for minute quantities, to about ^ a milligramme. If several different quantities of a substance are to be operated upon, the best way is to weigh off the several portions successively ; which may be accomplished most readily by weighing in a glass tube, or other appropriate vessel of known weight, the whole amount of substance intended to be devoted to the analytical process. Out of this tube the portions required for the several operations are taken, and the weight is ascertained each time from the diminution in the weight of the tube (compare § 10, 5). § 18. 2. ESTIMATION OF THE AMOUNT OF WATER CONTAINED IN A SUBSTANCE. If the substance to be examined contains water, it is usual, in the great majority of cases, to begin by determining the amount of this water. This Operation is generally simple; in some instances, however, it lias its difficulties. This depends upon various circumstances, viz., whether the compounds intended for analysis yield their water readily or not; whether they can bear a red heat without suffering decomposition, or whether, on the contrary, they give off other volatile substances, besides water, even at a lower temperature. The correct knovoleilye of the Constitution of a substance depends frequently upon the accurate estimation of the quantity of water contained in it; in many cases—for instance, in the analysis of the salts of known acids—the estimation of the amount of water contained in the analysed compound suffices to enable us to deduce the formula. The estimation of the amount of water contained in a substance, is, therefore, one of the most important, as well as most frequently occurring operations of quanti- tative analysis. The proportion of water contained in a substance may be determined in two ways, viz., 1, from the diminution of weight consequent upon the expulsion of the water; 2, by weighing the amount of water ex- pelled. A. ESTIMATION OF THE WATER FROM THE LÖSS OF WEIGHT CON- SEQUENT UPON ITS EXPULSION. This method, on account of its simplicity, is almost invariably resorted to in quantitative analysis, except in cases where it is inapplicable, from](https://iiif.wellcomecollection.org/image/b28133742_0061.jp2/full/800%2C/0/default.jpg)
