Dr. R. Hare on the Explosiveness of Nitre. 529 



This statement of Hayes caused me to recollect, that upon 

 one Occasion a mischievous explosion had occurred in my 

 laboratory, when a fissure taking place in an iron alembic 

 holding about twenty pounds of fused nitre, on hoisting the 

 alembic off the fire, a jet of the liquefied salt fell accidentally 

 upon some water in a tub, which was unfortunately too near. 

 It also brought to mind that potassium, when thrown upon 

 the surface of water, is, by combustion with the oxygen of 

 that liquid, converted into a fused globule of red-hot oxide, 

 which, in the act of combining with water, detonates violently. 

 This detonation struck me as being clearly owing to a sort of 

 double reaction, in which, while one portion of water, by 

 uniting with the oxide of potassium, converts it into hydrate 

 of potash, another portion, uniting with the heat, flies off ex- 

 plosively as steam. 



10. In a letter to Hayes, immediately after his explanation 

 appeared, I stated these facts and inferences ; and moreover, 

 I endeavoured to illustrate the subject by referring to the ex- 

 plosion so frequently produced by blacksmiths, through the 

 forcible contact with moisture, of incandescent iron struck by 

 a hammer. It has been ascertained that globules of oxide of 

 iron, as they fall in a state of fusion from a wire ignited in 

 oxygen, do not at first produce any commotion in water. 

 This arises from the generation of a protecting atmosphere of 

 rarefied aqueous vapour, which renders contact with the liquid 

 water impossible. Widely different would be the result, were 

 the liquid suddenly forced into contact with the globule by a 

 blow from a hammer, as above mentioned. Analogous causes 

 operate when globules of the most volatile liquids or solids are 

 retained for a time in the cavity of an incandescent metallic 



mass is instantly converted into steam, having the elastic force of that used 

 in steam-guns; exceeding gunpowder in destructive energy. The red-hot 

 particles, dispersed by the sudden action, pass over considerable spaces, 

 and the appearance of flame is produced. 



In cases where water falls on highly heated polished surfaces, such as 

 melted glass, copper, or silver, steam is formed rapidly, but silently ; the 

 water does not touch the hot surface. The spreading of a film or crust 

 over the polished surface instantly alters its relation to water, and causes 

 steam to form with explosive violence, attended by a loud report. 



I do not hesitate in expressing my belief, that the disastrous effects pro- 

 duced in New York were caused by water or other fluid falling on salt- 

 petre, while burning with the bags investing it. The facts which I have 

 stated may have interest or importance in connection with attempts made 

 to extinguish fire in buildings containing saltpetre. The danger of throw- 

 ing water on the fire is manifest, while the loss to the owner of the salt- 

 petre would doubtless be greater from water than from fire. 



Respectfully, 



Henri/ Williams, Esq. A. A. HAYES. 



Phil. Mag. S. 3. No. 253. SuppL Vol. 37. 2 M 



