130 NITRE DISCOVERED IN 



In the winter of 1799 I made those experiments on the 

 production of air from the freezing of water, an account of which 

 is published in the 5th Vol. of the Transactions of the Philo- 

 sophical Society of Philadelphia, p. 36; And having made 

 use of the same salt, mixed with snow, in every experiment, 

 always evaporating the mixture till the salt was recovered dry, 

 I collected the salt when I had done with it, and put it into a 

 glass bottle, with a label expressing what it was, and what use 

 had been made of it. 



This quantity of common salt having been frequently dis- 

 solved, and evaporated in an iron vessel, remained till the 26th 

 of last October ; when, having occasion to make a large quan- 

 tity of marine acid, and this salt appearing to be of little value, 

 I put to it an equal weight of acid of vitriol and about twice 

 the quantity of water, and began the distillation in the usual 

 way. But I was soon surprized to observe that red vapours 

 rose from it, first filling the retort, and then the adopter, &c. 

 and when the process was finished, returning to the retort, ex- 

 actly as in the process for making spirit of nitre. 



Not doubting, from this appearance, but that the produce 

 was the nitrous acid (though having used much water, the acid 

 was of course weak, and nearly colourless) I immediately 

 dissolved copper in it, and found that it yielded as pure nitrous" 

 air as any that I had ever procured in the same way. 



Examining the salt separately, I observed that when it was 

 thrown upon hot coals, whether those portions of it that were 

 white, or those that were brown from a mixture of the calx 

 of iron, it burned exactly like nitre; so that from this appear- 

 ance, I should have concluded that it had been wholly so. 

 But that it contained some marine salt, and that the acid pro- 

 cured from it had a mixture of the marine acid, could not 

 well be doubted ; and this appeared to be the case both by the 

 acid becoming turbid by a mixture of the solution of silver in 

 nitrous acid, and by its dissolving gold with the application of 

 heat, so that it was a weak aqua regia. 



This conversion of common salt into nitre appeared so ex- 

 traordinary, that I first thought there must have been some 

 mistake in the label, though few persons I believe are more 



