Publisher's Synopsis
This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1894 edition. Excerpt: ...ammonium salts are no longer present; but NH4Cl is necessary to prevent the precipitation of magnesium as hydroxid, and the consequent danger of missing it in its proper place. The addition of ammonia here will precipitate a small portion of the members of this group as hydroxids; but a study of the work that follows, and comparison of the solubility of hydroxids and sulfids of the members of this group, will make it clear that these hydroxids cannot be left as such after the treatment with (NH4)2S without leaving the way open to serious errors; that, nevertheless, the precipitate formed by NH40H can be left undissolved indicates another case of metathesis where only one of the reacting substances is in solution. All of the sulfids precipitated are quite insoluble in (NH4)2S except the NiS, which is slightly soluble; on this account any unnecessary excess of the reagent should be avoided. Two of the sulfids, FeS and CoS, are liable to be oxidized to sulfate on exposure to the air, or even perhaps by the oxygen dissolved in water ( 66): washing, as directed in 48 following, serves to avoid the error that one might fall into, if such oxidation were permitted, these sulfates being soluble in water. In the solution of such portion of the precipitate as is dissolved by HCl, the iron, in whatever form it was originally, is present now as a ferrous salt: but both for its final test and its precipitation by BaC03 in 58 h, it must be in the ferric form: only those hydroxids corresponding to the so-called sesquioxids, having the general form M203 in which M2 represents two atoms of a triad metal, are precipitated by BaC0 under the conditions of the treatment by that reagent: hence the treatment with HN08 in 52, Table VI. The separation..."
