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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![Presence of chlorides of the alkali metals, or of salts of the alkalies with oxygen acids does not interfere with the reaction; but the presence of cyanide of potassium, or of sulphide of potassium, will prevent it (J. Nessler). § 93. Special Reactions of the rarer Oxides of the first group. 1. Csesia (Oxide of Caesium), CsO [Cs,0], and 2. Rubidia (Oxide of Rubidium), EbO [Rb,0.] The CEesium and rubidium compounds are, it would appear, found pretty widely distributed in nature, but in very minute quantities only. They have hitherto been found chiefly in the mother liquors of mineral waters, and in a few minerals (lepidolite, melaphyr, carnallite). Cesium has been found in considerable quantities in poUux, and rubidium has been found in beetroot molasses and in the ashes of plants. The CEesium and rubidium compounds bear in general a great resemblance to the potassium compounds, more par- ticularly in this, that their concentrated aqueous solutions are precipitated by tartaric acid and by chloride of platinum, and also that those of them that are volatile at a red heat tinge the flame violet. The most notable characteristic differences, on the other hand, are that the precipitates produced by chloride of platinum are far more insoluble in water than the platinochlo- ride of potassium ; 100 grams water at 10° will dissolve 900 mgrm. of platino- chloride of potassium, but only 154 mgrm. of the platinochlonde of rubi- dium, and as little as 60 mgrm. of the platinochloride of caesium. Again,, the alums show great diftereiioes as regards their solubility in cold water; thus 100 parts of water at 17° dissolve 13-5 parts of potassium alum, 2'27 parts of rubidium alum, and 0'619 parts of cEesium alum. But above all, the flames coloured by cesium and rubidium compounds give spectra quite differ- ent fi'om the potassium spectrum (see plate of spectra). The CECsium spectrum is especially characterized by the two blue lines a and ^, which are remarkable for their wonderful intensity and sharp outline; also by the line y, which, however, is less strongly marked. Amongst the lines in the rubidium spec- trum, the splendid indigo-blue lines marked a and ^ strike the eye by their extreme brilliancy. Less brilliant, but still very characteristic, are the lines S and y. To detect both alkalies in presence of each other by the spectroscope, the chlorides should be taken and not the carbonates, as with the latter salts the rubidium spectrum is not always distinct in the presence of the caesium spectrum. (Allen, Heintz.) Lastly, we have still to mention that carbo- nate of CEesia is soluble in absolute alcohol, whilst carbonate of rubidia is in- soluble in that menstruum; a separation of the two oxides, however, is effected only with difSculty by this means, as they seem to form a double salt which is not absolutely insoluble in alcohol. It is more easy to separate them when they are in the form of acid tartrates; the acid tartrate of rubidia dissolves in 8'5 parts of boiling water, and 8457 parts of water at 25°, while the corresponding salt of cgesia dissolves in 1'02 parts of boiling water, and 1032 parts of water at 25° (Allen). (The acid tartrate of po- tassa requires 15 parts of boiling water, and 89 parts of water at 25°.) A separation may also be effected by adding stannic chloride to a hot solu- tion of the salts containing a rather large excess of hydrochloric acid ; under these circumstances caesium stannichloride separates as a sparingly soluble precipitate whilst the rubidium and potassium remain in solution. Care must be taken not to mistake the sparingly soluble ammonium stannichloride for ca)sium stannichloride (S t o 1 b a). 3. Lithia, LiO [Li,,0]. Lithia is also found pretty widely distribiited in nature, but in minute quantities only. It is often met with in the analysis of mineral waters and ashes of jjlants, less frequently in the analysis of minerals, and only rarely](https://iiif.wellcomecollection.org/image/b21966953_0115.jp2/full/800%2C/0/default.jpg)
