328 HEATS OF FORMATION OF THE CYANOGEN SERIES. 



they would share between them the base in the liquor. This 

 last supposition seems the more probable. 



In fact, on mixing the ferrocyanide with dilute sulphuric 

 acid we actually observe a progressive division of the base 

 between the acids and a displacement, which tends to become 

 total in the presence of a great excess of sulphuric acid. Among 

 the various experiments that were made with regard to this 

 question, the following only will be quoted : 



J[KJFe(CN) e (6 litres) + H 2 S0 4 (1 eq. = 2 litres)] disengages 



+ 1107. 



<L[K 4 Fe(CN)' 6 (6 litres) + 2eH 2 S0 4 (1 eq. = 2 litres)] dis- 

 engages + 0'181. 



Upon continuing the progressive additions of sulphuric acid, 

 an absorption of heat is produced owing to the formation of the 

 bisulphate. 



With a large excess, added all at once 



i[K 4 Fe(CN) 6 (4 litres) + 10H 2 S0 4 (1 eq. = 2 litres)] + 0-966. 



These phenomena may be compared to those in the reaction of 

 sulphuric acid upon chlorides, 1 although the values are some- 

 what different. They also show a progressive division of the 

 base between the two acids. If we admit that i[10H 2 S0 4 ] are 

 sufficient to abstract almost the whole of the potash from the 

 ferrocyanide, according to what happens in the case of chlorides, 

 nitrates, etc., we can calculate the heat, X, disengaged in the 

 action of dissolved hydroferrocyanic acid on diluted potash. In 

 short, + 15 '7 being the heat disengaged by the action of 

 sulphuric acid on potash, and 1/75 the heat absorbed in the 

 action of J[4H 2 S0 4 (diluted)] on [K 2 S0 4 ] in solution (so as to 

 form bisulphate), we shall get for the reaction we are seeking 



i[i(H 4 Fe(C]Sr) 6 = 4 litres) + K 2 (1 eq. = 2 litres)] gives off 

 X = 15-71 - 1-75 - J(0-97) = + 13-5. 



This number is, to all intents, the same as that which repre- 

 sents the heat disengaged (13'6) by the combination of hydro- 

 chloric and nitric acids with potash, whence it follows that 

 hydroferrocyanic acid is a powerful one, and may be compared 

 with the mineral acids. We know, in fact, that it displaces 

 carbonic and acetic acids. The apparent absence of thermic 

 reaction between hydrochloric acid and ferrocyanide in solution 

 is consistent with these results. 



6. Nothing is easier than to pass from this to the formation 

 of Prussian Uue. It was found, in fact, that - I 1 2[3K 4 Fe(CN) 6 

 = (4 litres) + 2Fe2(S0 4 ) 3 (1 equiv. = 2 litres) = (Fe 7 (CN) 18 

 (precip.) + 6K 2 S0 4 (diss.)] disengages + 2-54 to + 278, the 



1 " Annales de Chimie et de Physique," 4" s6rie, torn. xxx. p. 524. 



