3-16 On Numerical Proportions 



of oxygen more tliaii the particles of nitrous gas, and will con- 

 sequently have, as the representative form, an octohedron com- 

 posed of two molecules of azote and four of oxygen ; hut then, 

 as in all the other combinations where tlie volume of one of the 

 comj>onents is doui)lc that of the other, the volume of nitrous 

 gas will not change by the addition of oxygen : the greatest con- 

 densation which takes place appears to me to be ascribable to 

 this, namely, that in proportion as these octohedrons are formed, 

 they are combined in hexa-docahedrons, with tetrahedrons of 

 nitrous gas. As two molecules of oxygen are then sufficient for 

 the formation of one of these hexa-decahedrons into which two 

 entire particles of nitrous gas enter, the volume of oxygen is 

 only the fourth part of that of the nitrous gas, and the volumes 

 of azote and oxygen are, in the nitrous acid, as 4:6. These 

 results agree with the experiments of M. Berzelius. On this hy- 

 pothesis, the condensation ought to be 3 -fifths of the total vo- 

 lume; but it will not take place completely except when, the 

 oxygen being introduced by small portions into the nitrous gas, 

 the octohedrons just mentioned, in proportion n.s they shall bo 

 formed, will meet an excess of tetrahedron of nitrous gas with 

 which they maybe combined. If we introduced, on the contrary, 

 the nitrous gas into oxygen, a part of these octohedrons might 

 remain isolated, and there might result combinations and con- 

 densations in variable proportions. 



It follows from the composition of the nitric acid, as deter- 

 n\incd by Sir H. Davy, and which is confirmed by the decompo- 

 sition of the nitrate of ammonia, that a particle of this acid, if 

 we can obtain it without water, will be composed of one particle 

 of azote and of two particles and a half of oxygen. It will then 

 contain four molecules of azote and ten of oxygen ; and we may 

 conceive it as formed by the meeting of two tetrahedrons of ni- 

 trous gas joined to an octohedrcm of six molecules of oxvgen *, 

 and forming with it a dodecahedron. But in the combination 

 wliich this acid ahvays forms with water, we must su])pose that 

 the octohedron of oxygen and two octohedrons of water form a 

 trioctohedron which is united in a trapezoidal form with the two 

 tetrahedrons of nitrous gas : we may hence conclude. wliat is the 

 cpiantity of water in the most highly concentrated nitric acid, 

 and we find by calculation that it is nearly what Dr. WoUaston 

 has determined by his experiments. 



In the nitrate of ammonia, a particle of drv nitric acid is 

 united to two particles of ammoniacal gas; so that one particle 



'" We may also suppose that, in the foiiiiation of the nitric acid, the 

 hcx;»-Hecahedron of litrous acici is joined to a tetrahedron of oxyf;t-n, 

 wliich always forms a combination of an octohedron with two tetrahedrons, 

 and changes nothing in the following explanations, 



of 



