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.
151/526 page 127
![9 Ferrocyanide of potassium throws down green ferrocyanide of cobalt Co Cfy [Co,Fe(CN)„], insoluble in hydrochloric acid. 10 Perricyanide of potassium throws down browmsh-red ferri- oyanide of cobalt, Co3Gfdy [Co,Fe,(CN),,], insoluble in hydrochloric ''^^^ If bitartrate of potassa or chloride of ammonium is added to a solu- tion of a cobalt salt, then excess of ammonia, and lastly ferricyanide of ■Dotassium to the clear strongly ammoniacal solution thus formed, a deep vellowish-red hquid is obtained if it is concentrated, but rose-red'when Very dilute (Skey, Gintl). This is a very delicate reaction, adapted for the detection of cobalt in the presence of nickel. _ 11. The addition of cyanide of potassium to a cobalt solution ffives a brownish-white precipitate of protocyanide of cobalt, CoCy lCo(CN)..], which dissolves readily in excess of the precipitant as the double cyanide of cobalt and potassium. Acids precipitate cyanide of cobalt from this solution ; but if it is previously boiled with cyanide of potassium in excess, in presence of free hydrocyanic acid (liberated by adding one or two drops of hydrochloric acid), or if the solution is . mixed with potassa or soda and chlorine is passed through it without warming, or bromine water added, the double cyanide is converted into cobalticyanide of potassium, KJJoJJy^^KJJcdj [K,Co„(CN)i,], and acids will no longer produce a precipitate (essential difference iaetween cobalt and nickel). Mtrite of potassa and acetic acid added to the unaltered solution of the double cyanide produces a blood-red colour in consequence of the formation of nitrocyanide of cobalt and potassium; when the solution is very dilute, the colour is orange-red. Solution of soda added to the double cyanide produces a brown colour when the liquid is shaken up, oxygen being absorbed (C. D. Braun) : if yellow sulphide of ammonium is added, it turns blood-red (Tattersall ^nd Papasogli. These reactions distinguish cobalt from nickel). 12. Sulpliocarbonate of potassa, added to solutions which have been rendered alkaline by ammonia, produces a dark-brown colour, almost black; very dilute solutions become pale straw colour. 13. Carbonate of baryta behaves in the same way as with solu- tions of nickel. 14. If nitrite of potassa is added, in not too small proportion, to a solution containing protoxide of cobalt, then acetic acid to strongly acid reaction, and the mixture allowed to remain in a moderately warm place, all the cobalt separates in the form of a beautiful yellow crystal- line precipitate, from concentrated solutions very soon, from dilute solu- tions only after sometime (Fischer, Stromeyer). Stromeyer con- siders this precipitate to be a nitrite of sesquioxide of cobalt and potassa, Cop^.SKO.GNOg.SHO [K,Co,(NO,),,,3Hp]. The pre- <;ipitate is very perceptibly soluble in water, almost insoluble in concen- trated solutions of potassa salts and in alcohol, insoluble in presence of nitrite of potassa. When boiled with water, it dissolves, although not <;opiously, forming a red solution, which remains clear on cooling, and from which alkalies throw down hydrate of protoxide of cobalt. This excellent reaction serves well to distinguish and separate cobalt from nickel. 15. Borax dissolves compounds of cobalt in the inner and outer .flame to clear beads of a magnificent blue colour, which appear violet ■by candle light, and are almost black in the presence of a large quantity](https://iiif.wellcomecollection.org/image/b21966953_0151.jp2/full/800%2C/0/default.jpg)
