Licence: Public Domain Mark
Credit: Qualitative chemical analysis / by C. Remigius Fresenius. Source: Wellcome Collection.
Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.
114/526 page 90
![than in the wet way, and also with far greater delicacy, by the fliime coloration. We have seen, indeed, tliat the soda coloration com- pletely obscures the potassa coloration, even wlien the potassa salt contains but a trifling admixture of soda salt. With the aid of the spectrum apparatus, however, the spectra of the two are obtained so distinct and beautiful that a mistake is altogether impossible. And even without a spectrum apparatus the potassa coloration can always be distinctly recognized through the indigo or permanganate prism, or through a blue glass, even in a flame coloured strongly yellow by soda; the soda coloration again may be placed beyond doubt, if neces- sary, by the aid of iodide of mercury paper, or green glass, in the manner already described. The following methods serve for the detection of ammonia in ex- ceedingly minute quantities, as for instance in natural v/aters ; they depend on the separation of certain mercury compounds which are in- soluble in water, and which contain the nitrogen, or the nitrogen and part of the hydrogen of the ammonia. a. If water containing a trace of ammonia or carbonate of ammonia is mixed with a few drops of solution of mercuric chloride, a white pre- cipitate is formed, even in very diliite solution ; the precipitate consists of ]SrH,Hg.,Cl [NHoHgCI], and may be considered as a double amide and chloride of mercury, or as chloride of dimercurammonium: 2NH3 + 2HgCl = ]S]-H,Hg,Cl + NH^Cl [2NH. + HgCI,---- NH.HgCI + NH,CI]. If the solution is extraordinarily dilute, no turbidity occurs, but on the addition of a few drops of solution of carbonate of potassa or carbonate of soda, the Hquid will become turbid or opalescent after a few minutes. This reaction takes place when water containing a trace of a neutral salt of ammonia is mixed with a few drops of solution of mercuric chloride and a few drops of solution of carbonate of potassa or carbonate of soda. The precipitate which separates on the addition of carbonate of soda consists of 1 equivalent of the previously mentioned precipitate with 2 equivalents of oxide of mercury : NH3 -I- 4HgCl + 3(K0,C0,) = NH,Hg,Cl,2HgO + HO + 3KC1 + SCO, [2NH3 + 4HgCI, + 3K,c63=2(NaHgC!,HgO) + H,0 + 6KCI + 3CO,]. Too much mercuric chloride and carbonate of soda must not be added, otherwise a yellow precipitate of oxychloride of mercury would be formed. (Bohlig, Schliyen.) h. On adding to a solution of mercuric iodide and potassium con- taining potassa* a liquid containing ammonia, or an ammonia salt, a reddish-brown precipitate is formed if the ammonia is present in some quantitv; and even if only the most minute trace of ammonia is present, there is always a yellow coloration produced. The precipitate consists of tetramercurammonium iodide NHg J,2H0 [NHgJ,H,p]. The reaction is : 4(HgI,KI) + 3(K0,H0) + NH„ = NHg J,2H0 + 7X1 + 4H0 [2(Hgl..,2Kl) + 3KHO + NH,= NHgJ,H,0 + 7KI + 2H,0]. The application of heat promotes the separation of the precipitate. * Prepared as follows -.-Two grams of iodide of potijssium are dissolved iu 5 CO. water, the solution is heated and iodide of mercury added until the last por- tions remain undissolved. The mixture is then allowed to cool, and diluted with 20 c c, water. This solution is allowed to remain for soi](ie time, hitered, and U c.c of the filtrate mixed with 30 c.c. of a concentrated solution of potassa. isbouid the liquid turn turbid, it is allowed to stand for a time and the clear portion poured off for use.](https://iiif.wellcomecollection.org/image/b21966953_0114.jp2/full/800%2C/0/default.jpg)
