A F F 



willi any bafe. If, however, \vc put this caUuIation to the 

 tell of cxpeilmeut, we (liall fu.d whether the- !iqut)r be 

 dikited, or concentrated, or even brou>^ht to cryllalh/atiou, 

 that tlierc is not the fmallelt trace to be found of any difl'cn- 

 gaged acid. 



Btf;des the above, there are feveral other important ob- 

 j';ftions to Mr. Kirwan's theor)-, efpeeiully to thai part of 

 It in which he fuppofes equal quantities of re.il fulphuric, 

 iiitiic, and muriatic aeidj, to require for their faturation the 

 Liuic proportion of potarti. The force of thefe objeftions 

 has been acknowledged by Mr. Kiiwan in his treatife " on 

 the Jlrcnglh of acids anJ the compofition of neutral fahs ;" he 

 Jiaf, in confequence, deduced the proportion of real acid, in 



A F F 



nitrous and fulphuric acid«, from other lefs cxcopftiinabic 

 data ; fo that hii numerical ta!)l(; of the llrenglli of affinities 

 is now by far the moft coiiect of any that has yet been 

 conllrufted; and his fundanicntal principle, diat th« (jtianlity 

 ot bale required to falurate a given quantity of real acid, is i 

 true e:;preihon of the force of affinity between the acid and 

 the bafe, feems to receive additional confirmation in pio- 

 porlion to ihe advance of chemical knowledge. 



The following coneaed table of the quantity of bafe 

 taken up by loo parts of fulphuric, nitric, muriatic, and. 

 carbonic acids, is copied fr«n Mr. Kirwan's cfTay on tlir 

 analyfii of miueral waters. 



J V. I.a-ivs of AJfinhy. 

 Before tlie fubjeCl of affinity Wrts fo well underftood as it 

 io at prefent, or rather while ehemifts were net yet aware of 

 the extreme difficulty and uncertainty of their refeaiches, 

 all the known fatls were collcfted and claflitied, and from 

 them was deduced a mimber of general laws of affinity, 

 molt of which have been fince overturned, or tffentially 

 modified by later more accurate invelttgations. The enu- 

 meration of thefe laws, with fuch reftricfions as have been 

 induced by modem difcoveries, will form the fubjeft of this 

 feftion. 



1. Chemical affxmty t.-hes place only hetiveen bodies of different 

 natures. 



This necefTarily follows from the definition given in the 

 third feftion, by which chemical affinity was dilUnguifhed 

 from the attraction of aggregation or cohefion, by this very 

 circumftanee. 



2. ylfjimty tales place only hclween tie ultimate particles of 

 bodies. 



Where two fimple fubftances enter into combination, 

 this may be allowed to be the cafe, but certainly Joes not 

 happen when compound bodies unite with each other : thus 

 when oxygen and hydrogen combine together into water, and 

 oxygen and fulphur into lulphurlc acid, there is probably an 

 affinity between the rltiiiiate particles of oxygen with tliofc 

 of hydrogen in one cafe, and thoie oi lulphur in the other ; 

 but when water and fulphuric acid combine together, the 

 affinity takes place betweeu particles of water and of acid, 

 each of which is reloLvablc into its chemical elements, and 

 is, therefore, not in a ftate of ultimate diviiion. 



^. The afpnily which uny one body has for a fries of 

 others, is not equal it force towards each iiutividujl cf that 

 feries. 



It is probable that no t^vo fubftances can be found, xvhofe 

 feparate affinity for a third is perfeftly equal in fimilar cir- 

 cu:nllances ; that tuch inftanees, if they ever occur, are at 

 lead very rare, is obvious from all that has been faid con- 

 cerning- fingle and compound elective affinity ; the whole of 

 which effentially depends upun this law, and is at the fame 

 time a demonilration of its trutli. 



4. Chemical affinity may ad upon more than two fubjlances 

 at the fame time, and unite them into one compound. 



A confiderable number of triple falts has lately been dif- 

 icovered which feein to countenance thii law ; perhaps, 



Vol.. I. 



however, it is fcarcely yet eftabliflied beyond the rsach of 

 controverfy. In one fenfe, indeed, almoft all the-fah.s may 

 be faid to be compoimds of more than two fubftances,. 

 thus, fulphat of iron confifts of fulphur, iron, and oxygen ; 

 carbonat of ammonia, of carbon, hydrogen, azot, and oxy- 

 gen : but in thefe and fimilar cafes, it is univerfally allowed 

 that the affinity of a binary compound is totally different 

 from that of its elements : fo, the neutral fait, carbonat of 

 ammonia, is not held together by the concunent affinities of 

 its four primary elements, but by thofe of its two immediate 

 compound parts, carbonic acid and ammonia. Common 

 alum is ufually confidered as a proper triple fait, in which 

 the feparate affinities of fulphuric acid, alumine, and pota(h, 

 are afting on each other at the fame time ; of this, however, 

 there appears not the Icall evidence, for though the fait in 

 queftion may be made by adding together fulphuric acid, 

 alumine, and potaOi, yet the fame refult i-- obtained by 

 combining acidulous fulphat of alumine with lulphat of pot- 

 adi. Similar obicrvations m-ay be made on the ammofiaco- 

 magnefian and other triple i'ahs, as they are called. 



y. Chemical action icill not take place betiveen tzL'O bodiet 

 except one of them, at leaf}, is in ajluidflate. 



This, though more accurate than the ancient maxim, 

 " corpora non agunt nifi fint foluta," is obvioufly borrowed 

 from it. There are two kinds of fluidity, the elaftic and non- 

 elailic, and thefe require to be carefully dillingullhed from 

 each other : the firll, or the gaffeous, is for the moil part 

 very unfavourable to chemical combination, while the fc- 

 cond, or tiie liiiuid, (including both fufion and foluticn) is 

 one of the moll indilpenfablc circuiiifiances in all cafes of 

 affinity. 



a. Cbeniral affinity is in an in-crrfe ratio to the attraSion 

 of aggre^aiion. 



This would feein to be a neceffiiry dedudion from the 

 preceding law ; it is not, however, to be admitted without 

 many limitations. The aggregation of bodies may be de- 

 ftioyed by mete mechanical means to a certain degree ; fuch 

 is the effect of the operations of cutting, rafpiug, pound- 

 ing, &c. Now in all thefe, and fimilar cafes, the above law 

 holds llriAly ti-ue ; the cafe and rapidity with which bodies 

 are decompoled, or enter into new combinations bcin^r di- 

 reftly »s the quantity of furface that they prefent, or in- 

 verfely as their nialfes. Thus fluat of lime (fluor fpar) in 

 entire crrftals, ii whcJly unaffected by fulphuric acid, but in 

 O z pioportiufl 



