1821.] the Composition of Prussiates. 9 



I have already spoken in another place * of this phenomenon 

 and of the conjectures which may be made as to its cause. If, 

 at the time of decomposing some cyanurets, the temperature is 

 too high, the phenomenon of combustion would coincide with 

 the disengagement of azotic gas ; and it would appear that one 

 ouo-ht not to occur without the other, as we know with respect 

 to the superoxide of hydrogen, and also with the muriatic radical 

 (oxide of chlorine), that combustion and oxygen gas are produced 

 together at the same instant. With the cyanurets, this pheno- 

 menon is divided into two periods, as we have seen — that of the 

 decomposition of the cyanuret, and of the ignition of the remain- 

 ing carburet of iron. This circumstance gives fresh support to the 

 opinion, that, as happens with the superoxides, the igniferous 

 decomposition is composed of two operations, one of which con- 

 sists in the disengagement of a portion of oxygen, and the other 

 in the more intimate union with that which remains, and that 

 consequently any exceplion to our general experience, as that 

 the separation of two simple bodies should be accompanied by 

 'gnition, as happens in the combination of the stronger elements, 



ought not to exist. 



*& 



VI. On the Combination of Cijanurets with Sulphuric Acids. 



The cyanurets when treated with concentrated sulphuric acid 

 are more or less dissolved without being decomposed. Those of 

 iron and potash, of iron and barium, dissolve without any resi- 

 duum, and yield colourless solutions which sustain a heat 

 much above 212° Fahr. without decomposition. Some others 

 alter in appearance, a very small quantity being dissolved by 

 sulphuric acid, the greater part remaining undissolved by it, and 

 possessing new properties. When sulphuric acid is poured upon 

 a cyanuret reduced to powder, the mixture frequently becomes 

 considerably hot; the cyanuret increases in volume, becomes 

 pulpy ; and, if it is soluble in the acid, it disappears gradually, 

 and the mixture becomes liquid. It is requisite to have a great 

 excess of sulphuric acid to dissolve even the most soluble. If to 

 this solution a little water be added, it becomes turbid, and 

 deposits a part of that which it held in solution ; that is to say, a 

 part of the compound of the cyanuret with sulphuric acid. If 

 much water be added at once, the compound of the cyanuret 

 with the acid is decomposed, and superhydrocyanate of iron, 

 and a supersulphate of the other base are obtained ; or if the 

 cyanuret is insoluble, it reappears with its usual characters. 



If the acid solution of a cyanuret be left exposed to the air, 

 it gradually attracts moisture, and the new compound dissolved 

 is proportionally deposited, sometimes in a crystalline, and at 

 other times in a powdery form. On the other hand, if the solu- 

 tion of a cyanuret in sulphuric acid be heated, there is a certain 



* Essay on the Theory of Chemical Proportions, &c. Paris. 1810- Page'81. 



