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.
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![Acid tartrate of soda answers us n test for potassn still l^etter than free tartaric acid. The reaction is tlip same in kind, liut different in degree, being much more delicate with the salt than with the free acid, since where the former is used the soda salt of the acid combined with the potassa is formed, whereas Avith free tartaric acid the hydrate of the acid combined with the potassji is formed, and this tends to increase the solvent action of the water present on the acid tartrate of potassa, and consequently checks the separation of the latter, KO,NO, + NaO,HO,C,H,0,„ = KO,HO,C,Hp,, + NaO,NO, [KNO3 + NaHC,H,0„= KHC,H,0„+ NaNO,]. 5. If a potassa salt which is volatile at an intense red heat is held on the loop of a fine platinum wire in the fusing zone of the Bunsen gas- lamp (p. 23), the salt volatilizes, and imparts a blue violet tint to the part of the flame above the sample. Chloride of potassium and nitrate of potassa volatilize rapidly, the carbonate and sulphate less rapidly, and the phosphate still more slowly; but they all distinctly show the reac- tion, although decreasing in degree. If a more uniform manifestation of the reaction is desired, that is, a manifestation independent of the nature of the acid that may chance to be combined with the potassa, the sample need simply be moistened with sulphuric acid, dried at the border of the flame, and then introduced into the fusing zone. With silicates, a,nd other compounds of potassa which volatilize with difiiculty, the reaction may be ensured by fusing the sample first with pvire gypsum, as in this way silicate of lime and sulphate of potassa are formed, and the latter then readily colours the flame. Decrepitating salts should be ignited in a platinum spoon before they are attached to the loop. The sample of the potassa salt may also be held before the apex of the inuer blow- pipe flame produced with a spirit-lamp. It should be noted that the presence of a salt of soda completely obscures the potassa coloration of the flame. The spectrum of the potassa flame as observed by the spectroscope (p. 28, or p. 29) is shown in the coloured plate of spectra. It contains two characteristic lines, the red Hne a and the indigo blue Hue /3. If the potassa flame is observed through the indigo prism (p. 27) the coloration appears sky-blue, violet, and at last intensely ciimson, even through the thickest layers of the solution. Admixtures of lime, soda, and lithia compounds do not alter this reaction, as the yellow rays can- not penetrate the indigo solution, and the rays of the lithia flame also are only able to pass through the thinner layers of that solution, but not through the thicker layers; the exact spot where the penetrating power of the rays of the lithia flame ceases has to be marked hj the operator on his indigo prism. But organic substances Avhich impart luminosity to the flame might lead to mistakes, and must therefore, if present, first be removed by combustion. Instead of the indigo prism, Oornwall's permanganate prism (p. 27) or a blue glass may be used; if lithia is present, the absorbent medium must be sufliciently thick to keep out the red lithia rays. 6. If a salt of potassa (chloride of potassium answers best) is heated with a small quantity of water, alcohol (burning Avith colourless flame) added, the mixture heated, and then kindled, the flame appears violet.. The presence of soda obscures this reaction, which is altogether much less dehcate than the one described in 5.](https://iiif.wellcomecollection.org/image/b21966953_0110.jp2/full/800%2C/0/default.jpg)
