1821.] the Composition of Prussiates. 11 



alcohol : the undissolved salt was washed with alcohol, contain- 

 ing a very little caustic ammonia, in order to satisfy myself that 

 the undissolved sulphate of potash was neutral. The alcoholic 

 liquors were afterwards diluted with water and precipitated by 

 muriate of barytes. I obtained nine parts of sulphate of potash 

 and 40 parts of sulphate of barytes. An experiment of this 

 nature cannot be very exact ; for the substance to be analyzed 

 always contains some sulphuric acid on the surface. Thus in 

 this analysis the sulphate of barytes contains rather more than 

 three times as much sulphuric acid as the sulphate of potash. 

 Considering the excess of sulphuric acid as adhering to the sur- 

 face of the crystals, it follows that the cyanuret of iron and 

 potassium must have been combined with a sufficient quantity 

 of sulphuric acid to form a bisulphate with the potash, and com- 

 mon sulphate with the protoxide of iron. 



2. Ci/anuret of Iron and Barium with Sulphuric Acid. — This; 

 compound is much less soluble in sulphuric acid than the fore- 

 going. It crystallizes readily when made to attract moisture 

 from the air. The crystallized salt is decomposed by water and 

 by alcohol, and gives sulphate of barytes, hydrocyanate of iron, 

 and sulphuric acid. An analytic experiment, but which is less 

 deserving of confidence even than the foregoing, because the 

 crystals of the barytic compound are smaller, and consequently 

 retain more sulphuric acid, gave me a quantity of sulphuric acid 

 necessary to form bisulphates both with the barytes and the prot- 

 oxide of iron. 



3. Cyanuret of Iron and Lead was strongly heated in sulphuric 

 acid, but the new compound is almost insoluble. The sulphuric 

 acid added in excess is rendered slightly turbid by the addition 

 of a little water; but 1 observed no traces of crystallization even 

 after many weeks' exposure to the air. 



4. Ci/amuct of Iron and Cobalt readily dissolves in, and gives 

 a red colour to, sulphuric acid. After some hours, the liquid 

 deposits a crystalline powder of a very fine rose colour, and 

 loses at the same time much of its colour. I thought at first 

 that the rose powder might be sulphate of cobalt ; but when 

 water is added to it, it becomes at first green, and afterwards, in 

 proportion to the action of the water, it assumes the reddish- 

 grey colour of hydrocyanate of cobalt. In order to explain what 

 happens in this experiment, I ought to add, that when a solution 

 of cobalt is poured into one of cyanuret of iron and potassium, 

 there is at first formed a green precipitate which gradually 

 becomes of a reddish-grey colour. If it be dried and then 

 heated, it yields water and a little ammonia combined with car- 

 bonic and hydrocyanic acid, and resumes its original green 

 colour. The changes of colour, which resemble those that 

 occur with the muriate of cobalt, appear to depend on water, 

 which, when the green colour of the anhydrous cyanuret 

 changes and becomes reddish-grey, is absorbed, whether it forms 

 an hydrocyanate, or produces water of crystallization. As then 



