324 Dr. Thomson on [May, 



by him in his well-known paper, entitled '* Of a new Eudiome- 

 ter," (Phil. Trans. 1783, p. 106). It is, therefore, rather singular, 

 that this method, which is easy and exact, seems to be quite 

 imknown both to Mr. Dalton and M. Gay-Lussac. The method 

 is this : Put into a small glass vessel open below 100 volumes of 

 deutoxide of azote. Into a small cylindrical glass vessel having 

 a small brass stop cock at its top, and a brass plate (with a 

 small hole in it) fixed to it by grinding below, put 100 volumes 

 of common air. Sink the cylindrical vessel under water, and 

 place the vessel containing the deutoxide of azote over it, tak- 

 ing care that its mouth is under the surface of the water. 

 Things being in this situation, open the stop cock. The 

 common air will make its way slowly, and bubble by bubble, 

 into the deutoxide of azote. Agitate the vessel containing the 

 deutoxide of azote the whole time that the common air is enter- 

 ing into it. If you measure the residual gas after the process is 

 at an end, it w ill amount at an average to 96 or 97 volumes ; so 

 that the quantity of gas that disappears when the experiment i& 

 made in this way amounts to 103 or 104 volumes. 



Now 100 volumes of common air contain 21 volumes of oxygen 

 gas ; so that 82 or 83 volumes of the gas which have disappeared 

 are deutoxide of azote and 21 volumes oxygen gas ; but 21 : 83 

 :: 100 : 395-2. 



In this mode of experimenting then, 100 volumes of oxygen 

 gas unite to 395-2 volumes of deutoxide of azote. Now 395-2 is 

 only about one per cent, less than 400. I conceive, therefore, 

 that there can be no doubt when the experiment is made in this 

 way, that 100 volumes of oxygen gas really unite with 400 

 volumes of deutoxide of azote. 



Deutoxide of azote consisting of equal volumes of azotic and 

 oxygen gases united without undergoing any condensation, it is 

 obvious that 400 volumes of it must be composed of 



200 volumes oxygen 

 200 volumes azotic gas 



Therefore, when 100 oxygen unite with 400 deutoxide of azote, 

 the compound formed is in reality composed of 200 volume!3 

 azotic and 300 volumes oxygen ; or, which is the same thing, of 

 100 volumes azotic + 150 volumes of oxygen gas. Now this is 

 the compound called hi/ponitrous acid. 1 have never attempted 

 to collect this acid in order to examine its properties, the great 

 quantity of water with which it was diluted in all my experi- 

 ments precluding the possibiUty of obtaining it. But as this- 

 mode of experimenting gives uniforai results, I see no reason to 

 doubt that such a substance as hyponitrous acid actually exists. 

 4. 1 have never found any difficulty in obtaining a compound 

 of 100 volumes oxygen and 200 volumes of deutoxide of azote. 

 My method of proceeding is this : I introduce 100 volumes of 

 common air into a cylindrical glass tube, the internal diametev 



