204 On the Prussic and Prussous Acids. 



I wish also to observe, that the proportion of prussian 

 blue I have mentioned for boiling with the sulphuret is 

 much larger than is necessary, as 1 have since succeeded in 

 obtaining prussite of potash when the proportion of prussian 

 blue was only equal to that of the sulphuret, but long boiled 

 with the latter in two distinct and' equal portions. The 

 prussite of potash thus obtained is, however, mixed with a 

 much larger quantity of hydroguretted sulphurct than when 

 a greater portion of prussian blue is employed. 



Whether the prussous acid can be applied to any use, 

 time and future experiments must decide. It appears to me 

 to be a very delicate test of silver and of iron in solution. • 



The preceding experiments, by proving the presence of 

 oxygen in prussic acid, give it a stronger claim than it be- 

 fore possessed for being placed among the acids. 



The prussous acid possessing stronger acid properties 

 than the prussic is a curious, though not a solitary, instance 

 of the effect of oxygen in diminishing acidify, when its 

 quantity exceeds a certain fixed proportion; in this respect 

 the prussic acid is analogous to the oxy-muriatic. - 



To recur to the attempt which gave rise to the researches 

 that are the subject of this memoir, I beg leave to state, 

 that I have succeeded in producing pure triple prussiate of 

 potash, by stopping the process before the change which 

 produced the prussite ensued, and by subsequent purifica- 

 tion of the lixivium from sulphates and sulphites, by acetate 

 of barytes ; from sulphur by acetate of lead ; and, lastly, 

 from the acetate of potash thus formed by crystallization 5 

 but on account of the complication of this process, 1 hesi- 

 tate to recommend it for general use. 



Tower, London, April 21, 1809. ROBERT PoRRETT, Jun. 



p.S. — It is essential to the success of the experiment, in 

 which the prussicacid is regenerated from the liquid B by the 

 nascenthy per-oxygenized muriatic acid, that the excess of 

 acid remaining in the liquid, after the oxygenizing process, 

 should be neutralized by an alkali previous to pouring it into 

 the solution of iron, which should likewise be perfectly 

 neutral. 



May S, 1S09. PiOBERT PoRRETT, Jlin. 



XXXVII. Memoir 



