rubhi>h heap- l'ir instance, lime rubbish (in tin- presence of a base 



1 ' . ' ;i . 1 1 a IIKIIV or less considerable a ii K MI n t of nit re. ( Mu- 

 ff the>e nitres tin- sodium nitrate is extracted from the earth in 

 lai'u'e quantities in ('hill, \\here it \\a- probably formed li\" the oxida- 

 tion < >f animal refuse. Thi- kind of nitre is employed in practice for 

 the manufacture of nitric acid and the other oxygen compounds of 

 nitro-en. Nitric arid is obtained from Chili *<i/tji>-frv by heating it 

 with > -a! i>]< a r'i<- nfiil. The hydrogen of the sulphuric acid replaces the 

 sodium in t lie n it re. 1 he sulphuric a eid then lorm> either an acid -alt . 

 Nal 1S< .. or a norina] salt. Xa ,S( >,. while nitric acid is formed from the 

 nitre and i- volatilised. The decomposition is expressed 1 >v the equations : 

 (1) NaN< , II, S( ), = H N( ).,-u NallS* ),. if the arid salt he formed, 

 and (L ( ) L'.\aN< ).. + J I,S< ),=:Na,S< ), L' 1 1 N ( * . if the normal sodium 

 sulphate i> formed. \\'ith an excess of >ulphuric acid, and at a 

 moderate heat, and at the commencement of the reaction, the 

 decomposition proceeds according io the lirst etjuation : and <>n 

 furiher heating \\itli a >utlicient amount of nitre, according to the 

 second, because the acid .-alt NalIS(), itself acts like an acid (its 

 hydrogen bcin-- replaceable as in acids), according to the e<|iiation 

 N;i N < '., -f Nal IS( ) ,= Na,S( ) , + 1 1 N( ).,. 



1 he sidpliurie acid, as it is said, here displaces the nitric acid from 

 it - compound with the base. This not unfre<[tiently gives rise to the 

 supposition that sulphuric 1 acid has a particularly high degree of alhnity 

 or ener^v as compared with nitric acid, but. as we shall afterwards 

 see, the idea of a relathe allinity in acids and in bases is. in many 

 instances, untrustworthy; it should not be had recourse to so long 

 as ii be poible to explain a phenomenon without its introduc- 

 tion, inasmuch as the decree of atlinily cannot be measured. 1 he 

 aetion of the -ulphurie acid can be explained bv the fact that the 

 intrie aeii] formed is volatile. Nitric acid alone, ot all the sub- 

 stanee- ta]<in^ r part in the reaction, i^ capable of being converted into 

 \apour ia< the temperature emplo\'ed). and it alone volatilises : the 

 remainmir sub-tances are not volatile, or. more -trictlv speaking, are 

 \eryslighily \datile. I f we stijtpose thai the sulphuric acid is able to 

 .-et 1 fee e\en onl\" a >mall <|iiantl(v of nitrie acid tl'om its salt, it IN 

 ullicieiil for explaining e\ cnttially the complete decomposit i(n of the 

 nitre 1\ the suljihuric acid, bei-au.se, onee the nitric acid is separated, 

 it i -. on heating, eon \erted into \apour, and pa--es trom the sphere 

 of action of the remaining substances: the free .sulphuric acid then 

 a 'ja i n et - free ;i } Ye- 1 1 -mall < | u a 1 1 1 1 1 v of 1 1 it fie acid, a nd so on until the 

 nitric acid i- completely di-pku-ed from the nitre. It is c\ ident that, 

 according to this explanation, it is necessary that the sulphuric acid 



