places \\-ith ilif metal M an<l thus form the insoluble basie hydroxide, 

 or. a- it i- -aid. ijive a precipitate. The mechanism of this double 

 < le.-oiii.p< >-it it 111 is a> f ill iws : 



Thu-. for instance, if aqueous ammonia is added to a solution of a 

 -alt of aluminium. Ai, then hydrous alumina is separated out as a 

 colourless uvlat inous precipitate. '-- 



In order to ^ra^p the relation between ammonia and the oxygen 

 compounds of nitrogen it is necessary to reci i:_;ni.-e the general /<t/r of 

 fiiihxtitnt'ioii, applicable to all eases of substitution between elements,-'* 

 and therefore -howing what may be the cases of substitution between 

 ox\x f en and hvdrogen as component parts of water. The law of sub- 

 stitution may be deduced from mechanical principles if the molecule be 

 conceived as a system of elementary atoms occurring in a certain 

 eliemieal and mechanical equilibrium. \*>\' likening the molecule to a 

 ,-vstem of bodies in a state of motion for instance, to the sum total of 

 tin- sun. planets, and satellites, occurring in conditions of mobile equi- 

 librium then we should expect the action of one part, in this system, 

 to be etjual and opposite to the other, according *:o Newton's third law 

 of mechanics. 1 fence, being i^iven a molecule of a compound, for 

 instance. !!.,(). N I I :t , .Nad, IK'l. Arc., then its every two parts must 

 in a chemical respect represent something alike in force and capacities, 

 and therefore <//// tiro part* into ////!/// <i mo/ccn^- <>f compound ///"// 

 /,. ,l',,-'i'l'-<l di'i <-<ij,<thl< of ri'iiliH'luy eachothvr. In order that the api>li- 

 eat ion of i he la\\ p should become clear, it is cvidenl that amoii' f com- 



\ ' 'i lij i liyl rates ttii'iii pt'ciuijir c 



I pi in- iif an nia aili 



Mi' imi nf a t'n-sli iiiiant it y 

 l|. Mini .if tl... !M- l, 



:h-, 



it fliLii-iiir. a- wi- -li.ill afteruanls mmv iull\ l.-iii 



: , ,. n. III. -n ll." ivacti.m l,y \\hicli sudi an ^xrha !,-, i, a.T, .ni| .1 i-hr,! pr,,- 

 nl.-'itin .All CI, \('l ; HCI, M. tliiit two Mil-planers. All siinl clili.riiH-, 



litiil ..I .me i-li-iuriil. .1. li\ an. .tin r. A. ilm-s n..| aluay^ pro- 



. r;. r.i ' i..-.-..i.ipli -linl l,\ lli.' jn-ti.-u nf III.' f n-.- .-li-iu.-iMs. Lilt tin- snl.sti- 



. i -i -i ' i ' ' 1 1 . "in' I'm- aiml IHT. t'.irniN t In- nni-1 i-iniiii t-a-r "f (t.xidat ion 



! '1 tin' 1 i .'...; nl i-l it nt i"! i. I ha \ . i n \ ic\\ t \\,- nl ,-,) il lit imi 



.i'-,'- ill n t! "I ,, ;,,. n i-i. i-iit. if n I'ru of 



:. c..Jii|i..iiii<l In- K-II..UII. 



