528 Dr. R. Hare on the Explosiveiiess of Nitre. 



9. I owe it to my friend, Augustus A. Hayes, to state, 

 that I might have adopted the more general impression, had 

 it not been for his inferences and experiments made with the 

 view of accounting for the explosion of a vessel, loaded with 

 nitre, while lying at anchor in the harbour of Boston. It was 

 ascertained by this able chemist, that when, by an experiment 

 made in his laboratory, between 100 and 200 pounds of nitre, 

 intensely heated in a crucible, were suddenly sprinkled with 

 water, an explosion ensued*. 



* The subjoined quotation from the Boston Daily Advertiser, will serve 

 to show the point to which Mr. Hayes had attained in elucidating the 

 mysterious explosions produced by incandescent nitre, when my efforts 

 to afford a further elucidation commenced. 



Roxbury Laboratory, 28th July, 1845. 



Dear Sir, — Your note of yesterday, in relation to the explosive action of 

 saltpetre, has this moment come to hand. I most cheerfully comply with 

 your request in placing before you the facts connected with the subject of 

 the action of saltpetre on substances usually called combustible. 



Saltpetre, or the nitrate of potash or soda, alone, does not burn or ex- 

 plode by heat, however intense. It parts with one of its constituents, oxygen, 

 by heat, and it is to the combination of its oxygen with other bodies that it 

 owes its power of burning with them. Wood and other fibrous substances 

 do not burn with saltpetre until they have become partially charred ; they 

 then produce deflagration, or burn with sparks. A large quantity of salt- 

 petre, enclosed in gunny bags, as it is usually stored, after fire was commu- 

 nicated to it, would burn with the bags, emitting much smoke and sparks, 

 precisely as paper which has imbibed saltpetre would. It would not be 

 consumed ; only the small quantity required to burn with the bags would 

 be changed. If an addition of burning wood or charcoal were made to the 

 extent of one-fifth the weight of the saltpetre, ah intense and continued 

 deflagration would result, and all the saltpetre would be changed. No ex. 

 plosion would follow from applying fire to mixtures of charcoal, or wood and 

 saltpetre] the rapid combustiou called deflagration would be produced, but, 

 unlike explosion, time would be required for the mutual actions; and 

 where the quantities were large, many hours would be necessary before 

 they would cease. The recent destruction of life and property in New 

 York, the loss of a homeward-bound Indiaman and her cargo, by a similar 

 cause, have created an anxiety which has led to many inquiries respecting 

 the origin of the explosions attending the burning of saltpetre. I need not 

 remind you of a case which occurred at Central Wharf, about ten years 

 since, when the Hartford Packet was destroyed. The testimony obtained 

 in the last instance led me to make some experiments on the effects pro- 

 duced by dropping water on a burning mixture of saltpetre and charcoal. 

 It was ascertained that a very small weight of water, relatively to the salt- 

 petre, caused explosions, which might be made successive, so long as the 

 materials remained. The quantities of the substances acting being in- 

 creased to between 100 and 200 pounds, the addition of water, in the form 

 of spray, caused an explosion which destroyed the vessel, and shook all the 

 buildings in the vicinity. The temperature of a burning mixture of salt- 

 petre and charcoal, at the points of contact, is superior to that of " white 

 hot " iron, and the form is that of a bubbling fluid. Water falling on the 



