36 PHOSPHORESCENCE 



nutes, and increases in brilliancy as the tempera- 

 ture rises. 



Potassium also becomes incandescent when em- 

 ployed in the preparation of boron, as must have 

 been remarked by any chemist who has prepared 

 this metalloid. For this purpose vitrified boracic 

 acid, in fine powder, and potassium are heated in 

 a metallic tube. 



In fact, light, often accompanied by heat, is 

 evolved, wherever chemical action is very intense. 

 For instance, when sulphur and lead are melted 

 together, light is produced whilst the combination 

 of these two substances takes place. The same 

 is remarked when phosphorus and iodine act upon 

 each other : the experiment is very striking, and 

 occurs when small quantities of phosphorus are 

 covered over with iodine, at the ordinary tempe- 

 rature of the atmosphere. In a short time the 

 whole takes fire spontaneously. I have seen the 

 same occur when a crystal of nitrate of copper 

 was enveloped in a thin sheet of tin. 



When arsenic or antimony are thrown into chlo- 

 rine gas at the ordinary temperature, the metals 

 (which must be in fine powder) burst into flame 

 while combining with the chlorine. When caustic 

 baryta is placed in a capsule and concentrated 

 sulphuric acid poured upon it, the baryta becomes 

 incandescent. 



If a drop of water fall into a bottle of anhydrous 



