90 CHLORINE AND IODINE. 



now explain. I formed a quantity of hydriodate 

 of potash, and by a careful analysis, satisfied 

 myself that it is composed of an atom of hydrio- 

 dic acid, united to an atom of potash. When this 

 salt is exposed *to a pretty strong heat in close 

 vessels, it gives out water, and is converted into 



iodide of iodide of potassium. After a variety of trials, I 



potassium. *- J 



found that when 2O5 grains of this iodide of 

 potassium are dissolved in a small quantity of 

 distilled water, and the solution mixed with a 

 solution of 20 '7<5 grains of dry nitrate of lead, a 

 double decomposition takes place : iodide of lead 

 is precipitated, and the residual liquid is trans- 

 parent and colourless, and neither altered by 

 sulphate of soda, nor by nitrate of lead, showing 

 that it contains no sensible quantity of oxide 

 of lead, or hydriodic acid. The residual liquid 

 being evaporated to dryness, furnished 12'7<5 

 grains of salt-petre. But 12'75 grains of salt- 

 petre (as will be seen in the next chapter) con- 

 tain 6 grains of potash, equivalent to 5 grains of 

 potassium. Consequently, the 2O5 grains of 

 iodide of potassium contained just 5 grains of 

 potassium. The remainder consisted of iodine. 

 From this it appears that iodide of potassium is 

 a compound of 



Potassium 5 



Iodine 15-5 



20-5 



