1818.] of the Elements of Nitric Acid. 351 



I employed the decomposition of nitrate of potash by heat ; 

 one of the first chemical experiments which I ever made.* 



The capacity of a luted porcelain retort was ascertained by 

 filling it with fine sand : 15 grammes (231-66 gr. troy) of pure 

 and dry nitre were put into it. From the beak of this retort, a 

 tube passed to a ^top-cock, which was fixed in the upper end of 

 a glass jar filled with water, and standing upon the water 

 trough. The retort was heated at first slowly, and at last 

 exposed to all the heat of a reverberatory furnace, surmounted 

 with a tube six decimetres (29*6 inches). The whole was 

 allowed to cool. Water was then poured into the water trough 

 till the surface of the water in the jar and the trough were upon 

 a level. The stop-cock was now shut, and the retort broken ; 

 the potash was found united with the surface of the porcelain. 

 Sulphuric acid being poured upon this compound, no effervescence 

 took place. This shows us that the nitre had been entirely 

 decomposed, and that the potash had not retained oxygen. 

 However, there was sublimed in the tube a small quantity of 

 salt which weighed nine centigrammes (1-4 grain), and was a 

 mixture of nitrite and nitrate. 



The bulk of the gas disengaged was 4-8073 litres (293*38 cubic 

 inches) ; at the temperature of 53*6°, and when the barometer 

 stood at 0*7613 metre (29*973 inches), the volume of gas con- 

 tained in the retort before the experiment was 0*2997 litre 

 (18*29 cubic inches). 



Four analyses were made of the gas collected in the glass jar, 

 three by means of Volta's eudiometer, and one by means of the 

 hydroguretted sulphuret of lime saturated with azote. The 

 results were as follows : 



First analysis 65*96 per cent of oxygen. 



Second ditto 65*98 



Third ditto 66*16 



Fourth ditto 66*00 



Mean 66*02 



It was supposed that the gas remaining in the retort after the 

 process was precisely similar to that in the glass jar • because 

 the communication was very free, and the great change of tem- 

 perature which took place ought to have occasioned an equal 

 mixture. 



* I presented on Jan. 17, 1778, to the Academy of Sciences, a memoir, in 

 which 1 showed that the acid of nitre could be entirely converted into gas by the 

 action of heat, or at least that the only poition not thus changed was quite insigni. 

 fic.int : that by that method 580 cubic inches of gas might be obtained from an 

 ounce of nitre : that this gas consisted chiefly of oxygen, which afforded an expla- 

 nation of the effects of nitre upon charcoal and sulphur: that dried nitre contained 

 no sensible quantity of water ; and that at a certain stage of the decomposition the 

 nitrate was changed into a phloghticalrd nitre, or into a nitrite, which preserved 

 its neutrality. — Memoires del'Academie des Sciences, 1761. 



