XXVI. On the nature of the salts termed triple prussiates, and on acids formed by the union of certain bodies with the elements of the prussic acid

• Published in: Philosophical Transactions of the Royal Society of London
• Format: Article in Journal/Newspaper
• Language: English
• Published: The Royal Society 1814
• Subjects: Carbonic acid
• Online Access: http://dx.doi.org/10.1098/rstl.1814.0027; https://royalsocietypublishing.org/doi/pdf/10.1098/rstl.1814.0027

Since the admirable experiments of Scheele on the Prussic acid, chemists have distinguished between the salts formed by the direct combination of this acid with alkaline or other bases, and those obtained either by adding to the salts just mentioned a certain portion of a metallic oxide, or by decomposing by the alkalies a prussiate of a metallic oxide. Thus for instance, the salt formed by the union of the Prussic acid with potash has been called the simple prussiate of potash, while that ob­tained by boiling a solution of potash on Prussian blue has been called the triple prussiate of potash and iron, it having been proved that the black oxide of iron enters into its composition. The differences between these salts are very remarkable, the simple prussiate is always alkaline, is soluble in alcohol, is incapable of forming Prussian blue when added to the salts of per-oxide of iron, gives a yellow precipitate with salts of per-oxide of copper, is decomposed at the temperature of boiling water, and has its acid displaced by the carbonic acid. On the contrary, the triple prussiate is neutral, is insoluble in alcohol, forms Prussian blue with the salts of per-oxide of iron, gives a reddish brown precipitate with salts of per-oxide of copper, is not decomposed at the boiling temperature, nor in the least altered by carbonic acid. To the black oxide of iron, therefore, existing in this salt, chemists have attributed its superior permanency to the simple prussiate, and also its conversion to the neutral state. The latter effect of the oxide of iron is without a parallel in chemistry, no other alkaline salt is known which can be rendered neutral by the mere addition of black oxide of iron, which in all other instances will neutralize acids instead of alkalies. This however is not the only anomaly which the triple prussiates present, the following being also very remarkable. The black oxide of iron contained in them cannot be thrown down by the addition of any of the hydrosulphurets, succinates, gallates, or any other ...