220 Mr JOHNSTON on the Combination of Chlorine 



1 Chlorine, 4*5 ") 



2 Cyanogen, 13'03 



united to 4 atoms of potassium. Or, lastly, it may have united 

 with the whole of the cyanogen and the iron, as they exist in 

 the ferro-cyanic acid, forming a new acid, composed of 



1 atom chlorine, 4'5 } 



6 ... cyanogen, 19'5\=.31. 



2 ... iron, = 7'0\ 



and our new salt will consist of 



1 atom chloro-ferro-cyanic acid, 

 4 ... potassium, 



= 811 



= 20 1 81 ' 



forming a chloro-ferro-cyanide of potassium. 



The last of these views of the constitution of the salt is that 

 which I am inclined to adopt. For this preference various rea- 

 sons might be stated, but I am mainly influenced by the circum- 

 stance, that, when the chlorine combines with the prussiate of 

 potash as above detailed, it expels all the water, and therefore 

 seems to combine with the whole assemblage of elements as one 

 compound atom. 



10. The acid, as it exists in the above salt, can, it is obvious, 

 contain neither oxygen nor hydrogen. It may be obtained in a 

 separate state by various processes, some of which I shall ex- 

 plain in a future communication. I may here, however, men- 

 tion, that, when pure, it forms beautiful red four-sided needles, 

 not differing in appearance from those of any of its salts. In this 

 state it contains either water or its elements, and may be viewed 

 as a hydracid, though in the salt of potassium it acts precisely as 

 chlorine does in the chlorides. 



I have formed the various salts resulting from the union of 



