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Of all the metallic fubftances, 

 mercury feems to be the beft to 

 obtain nitrous air of a conftant qua- 

 lity ; but heat muft be applied, if a 

 large quantity is required in a ihort 

 time. I made ufe, a long while 

 ago, of pin-duft, of which a fmall 

 quantity, put in diluted fpirit of ni- 

 tre, yields all on a fudden a large 

 quantity of nitrous air of an equal 

 degree of ftrengih : but as the fo- 

 lution is very tumultuous, and a 

 great deal of the pin-duft, together 

 with the nitrous acid, is apt to rum. 

 out of the phial, I found it at laft 

 better to ufe common copper. I 

 coil flrong copper wire, neeled fo as 

 to be flexible, up in fmall curls, 

 and fill the phial with them. Thus 

 the nitrous acid, diluted with five 

 or fix times its quantity of water 

 being poured in it, finds a large 



and 



