216 Mr JOHNSTON on the Combination of Chlorine 



Now the chlorine may either have united itself to the entire 

 elements of the salt, or it may have expelled a portion of the 

 cyanogen, and have taken its place. The whole loss of gaseous 

 matter, which he concluded to be all cyanogen, but which was in 

 reality the sum of the two gases, GMELIN found to amount to 

 49 per cent. Now 3 atoms of cyanogen n 38'2 per cent, leaving 

 upwards of 10 per cent, for the chlorine added to the original 

 constituents. This is not far from half an atom (iz 8*82 per 

 cent.), which we shall afterwards see is the true quantity. 



4. Failing to satisfy myself by analysis of the true amount of 

 the chlorine, I endeavoured to ascertain how much the prussiate 

 of potash would absorb. And first, as the new salt contains no wa- 

 ter, 40'3 grs. of the anhydrous prussiate, the three atoms of wa- 

 ter being previously expelled by a gentle heat, were introduced 

 into a glass tube, and exposed for several days to an atmosphere 

 of chlorine : the white powder became of a beautiful bright yel- 

 low colour, and had gained T4 grs. Dissolved in water, it gave 

 a bright yellow solution, and by evaporation crystals partly red 

 and partly yellow, being a mixture of the new salt and the com- 

 mon prussiate. The powder, therefore, had not been saturated 

 with chlorine. 



5. I now introduced 150 grs. of the crystallized prussiate, re- 

 duced to a fine powder, conceiving that the presence of the 3 

 atoms of water might facilitate the combination. And to ascer- 

 tain if any gas were disengaged from the salt, I caused the one 

 end of the apparatus to terminate in a solution of the prussiate 

 of potash, through which the passage of chlorine would be indi- 

 cated by a change of colour ; while at the other, the chlorine was 

 generated and made to pass over chloride of calcium. As soon 

 as the gas came in contact with the powder, it gave it a deep 

 chrome-yellow colour, and a deposition of moisture took place on 



