If 3 2 PRELIMINARY OBSERVATIONS. 



rr - ) for hydrocyanic acid -f^, and not-^-^. That the hy- 



C/ 2 v^2 ^2 



drogen of hydrocyanic acid is chlorous and not basic, appears 

 in its being replaced by chlorine, with formation of hydrochloric 



NCI 



acid and the chloride of cyanogen, _ .. Hence, also, the lit- 

 tle action of potash and strong bases upon hydrocyanic acid 

 (page 989), its hydrogen, unlike that of ordinary hydrogen acids, 

 being chlorous, while the same hydrogen is readily replaced by 

 the more chlorous metals, such as mercury, the cyanide of mer- 

 cury being . The latter salt is not decomposed by strong 

 acids, as it would be if its constitution resembled that of cya- 

 nide of potassium . But cyanide of mercury is readily 



decomposed by sulphur and sulphuretted hydrogen, and by 

 hydrochloric acid, sulphur and chlorine assuming the mercury 

 and forming sulphuret and chloride of mercury respectively, 

 while hydrogen is left in the place of the abstracted mercury, 



and hydrocyanic acid -^ reproduced. 



The two atoms of cyanide of hydrogen, which exist in ferro- 

 cyanic acid, FeCy -4-2HCy, have, on the contrary, the constitution 

 of an ordinary hydrogen-acid, the hydrogen being strongly basic 

 and easily replaced by the basic metals, potassium &c. while 



the iron is not. It thus contains ^TTJ-' But the * ron ^ t ^ ie 



associated cyanide of iron not being precipitated by potash (re- 

 placeable by potassium), must be chlorous; and this metallic 

 cyanide, therefore, resembles ordinary hydrocyanic acid in con- 



NFe 

 stitution, or is 



Ferrocyanic acid ... 

 Ferrocyanide of potassium. _ 



^2 * 4--2 



The molecular formulae for ferricyanic acid (H 3 -}-Fe 2 Cy 6 ), 

 and forferricyanide of potassium (K 3 + Fe 2 Cy 6 ), deducible from 

 the same principles, are : 



