Instruction in chemical analysis : (Qualitative) / With a preface by Prof. Liebig. Edited by J.L. Bullock.
- Carl Remigius Fresenius
- Date:
- 1846
Licence: Public Domain Mark
Credit: Instruction in chemical analysis : (Qualitative) / With a preface by Prof. Liebig. Edited by J.L. Bullock. Source: Wellcome Collection.
55/412 page 33
![§ 24.] REAGENT PAPERS. 38 which are soluble in potass, and insoluble in ammonia, for in- stance, alumina, oxide of chromium, &c. &c. In this process, the elements of the sal ammoniac transpose with those of the potass, and this transposition results in the formation of chloride of potassium, water, and ammonia. Sal ammoniac is applied also as a special reagent for the precipitation of platinum as ammonio- chloride of platinum. c. Reagents which serve principally to separate or otherwise to characterize groups of substances. % 24. 1. REAGENT PAPERS. a. BLUE LITMUS PAPER. Preparation.—One part of litmus of commerce is to be digested with six parts of water; the solution is subsequently to be fil- tered, and the intensely blue filtrate divided into two equal parts ; —the free alkali in the one part is then to be saturated by stirring with a glass rod which has been dipped previously into very dilute sulphuric acid, and repeating this process until the fluid begins to look red; the other part of the filtrate is now added to the reddened fluid, and the whole mixture poured out into a basin, where slips of fine unsized paper are finally drawn through it. These slips are afterwards suspended over threads, and left to dry. The color of litmus paper must be perfectly uniform, and neither too light nor too dark. Uses.—Litmus paper serves to detect the presence of free acid in fluids, since acids change its blue colour to red. It is to be borne in mind, however, that the neutral salts of most of the heavy metallic oxides produce the same effect. ft. REDDENED LITMUS PAPER. Preparation.—Blue tincture of litmus is stirred with a glass D](https://iiif.wellcomecollection.org/image/b29300940_0055.jp2/full/800%2C/0/default.jpg)
