A F F 



A F F 



ArnxiTY is more particularly ufcJ iii fpcakiiig of tlie 

 relation or rmllitude between lascuaces, occafioniil by 

 tiieir bein;^ Ji-rived from the fame fource. 



We ule iihb affinity of words, fouiuis, &c. 



Arris IT V, jiffin'tli, Yv. I'tiivnnilfchiifl., Gcnn. Fni- 

 ntiitt/t, Swcd. yltlruHion of compojUion — Elective tilh-n^liun 

 iti Bergman. 



Tiiis term, wliich in its pi-oper and oripjinal fenfe fignitics 

 a prc'),i!nity of relationlhip, lias been adopted by niodcni 

 pliilurnphcrs as tlio expivHion of a foive purely chemical, 

 bv which fiibllaiices ot dilfereiit natures arc made to com- 

 bine with i-ach other. Tin's paiticiilnr metnphorical ule of 

 the word is not, however, of very old Kandinjj. I'archiifcii 

 is probably the firll who introduced it ; fpcaking; ot the 

 liitlWiilty of obtaining chemical elements perfectly pine, he 

 accounts for it in the following way, " Archim cnim atqiie 

 reciprocam inter fe habent a^imtalem." Boerliaave, how- 

 ever, contributed more than any other to bring the word 

 into common uft ; thus we tind in his Klementa Chemix ; 

 " Particulse folventes et t'ohit;c fe nffimlate fuic naturae, 

 collignnl in toqiora homogenea." Bergman has preferred 

 the tenn nllmilion, as more conformable to the precifion 

 of fcientific language; fince, however, all bodies in nature 

 attract each other, while chemical afTuiity cxitls only between 

 particular fnlillanccs, it feenis upon tlie whole more co'i- 

 vcnient to appropriate a term to the ixpreirion of this par- 

 ticular force, v.ithout, however, rigoroiidy excluding the 

 fyuonvmous phr.ife e/eiiive alliacl'rm, which the high au- 

 thority of Bergman has introduced into the chemical nomen- 

 flature. 



In treating of fo important a fubjeft as chemical affinity, 

 it will be neeelTar)-, for the fake of clearnefs to divide it 

 into fix fectioiis. 



The full will contain a (l;etch of the progrefs of dilcove- 

 ries in affinity. 



In the fecond the caufe of affinity will be difcufTed. 



The third will treat of fingle and compound affinity, and 

 the conilniiSlion of tables and fchemes. 



In the fourth the feveral methods of ellimating numerically 

 the force of affinity will be conlidercd. 



The fifth will contain the laws of affinity. 



The iixlh will be appropriated to the confideration of 

 pertain anomalies. 



§ I. H'tjlory of jlfuiily. 



The general fart that all fubitances have not the fame 

 relative degree ot affinity for each other, mull have been 

 obferved as foon as the fmalleft attention began to be paid 

 to chemical piienomena, and in the firll rude attempts to 

 explain the caufe of this difference of force, recourfe was 

 iiad to the maxim of Hippocrates, 0;lcoi» sfjjslKi ^p-,,- to oijiont, 

 Jtmilc v-nif ail Jimile. This doctrine of the old fchool we iUU 

 find in Heccher, who fuppofcd that there was a hidden prin- 

 ciple of fimilitude in all fiibftances capable of mutual che- 

 mical combination. Another feci, at the head of whom 

 was Lemery, endeavoured to explain chenVical agency by 

 confitieriug folvents as compofed of a multitude of fine 

 points, and thus mechanically predifpofed to enter the pores 

 iTid feparate the particles of fublhmces cxpoicd to their 

 aclion. 



Stnhl, h.owever, re'icAing the hypothefis of mere mechani- 

 cal forces, attributed the power of menilrua to the attradion 

 of contact or intimate cohelion ; for, to ufe his own lan- 

 guage, " eombiniiliones quafcumque non alitcr fieri quam 



" per arclam appofitionem." " Non per modum cuuei, 



"•' neque per modum incurfus in unam particulam feparan- 

 " d^m, fed putius per modum appreheolionis feu ajctae ap- 



" plicationis." Tliis eminent cheu'.ifi alfo diduced from 

 his experiments a variety of fafts and oblei-vations, tending 

 to prove that an union cmce formed could not be difiblved 

 without a luoiv intimate union of one of its conllituent parts 

 with another lubllance. 



It is to Geoffroy, the elder, that chemifliy is indebted for 

 the happy idea of collecting thefe fcatlered facls, and 

 Ikctciiing the outlines of the general rules of analyfis and 

 compolition. In the year 171S, he prefented to the Royal 

 Academv of Sciences at Paris the firll table of affinity, or 

 as he calls it, •' Des diflerens rapports oblerves en chymie 

 entre dilicientes fubllances," (fome of the different relations 

 obferved in chemilliy between different fubllances). This 

 table, which merits prefervation, as a curious hiftorical 

 ineniorial, and the pattern of all that have appeared fince, 

 coi'.filfed of only feventeen c-olumns very imperfectly filled, 

 and prefented rules, which for the inoll part have been 

 changed or coiifiderably modified. With all its errors, 

 however, it ia jiillly to be confidered as the bafis and guide 

 to all our chemical knowledge : it has been enlarged and 

 improved, but llill retains its original form and eflence, and 

 as the great fabric of experimental fcience advances towards 

 peifeClion, fi> will this, which is its epitome and model. 



Ko very material improvement appears to liave been made 

 on Crcoifrov's table till C/ellert, the celebrated profeffor of 

 Frevburg, publilhed, in i^jo, his Ch\inia Metallurgica ; 

 in this work was contained a new table of affinity extended 

 to 2S columns, and at the bottom of each was a fill of 

 fubllances which he had found not to be acled on by the 

 body placed at tlie head of the column. Rudiger, in 1756, 

 inferted in his fyllem of Chemillrv a table of affinity reduced 

 to 15 columns, in which the fixed alkalies and lime are 

 placed parallel with each other, and before ammonia in the 

 column of acids : he alfo added, in a fmall fupplementary 

 table, thofe bodies which refufcd to combine without the 

 intervention of a third. 



In confequence of a prize offered hv the Academy of 

 Rouen, in 175H, a very important additicui was made to 

 the table cf affinities bv M. Limbourg ; he extended the 

 number of columns to 33 ; he afcertained that zinc (hould 

 be placed at the head of the metals in the column of acids, 

 and that it preciiiitated them all, even by the dry way ; he 

 maintained, that lime and the fixed alkaUcs acled by means 

 of affinity on animal matter ; and pointed out feveral cafes 

 in which the order of affinities was changed by the in- 

 fluence of temj)erature or the volatility of one of the in- 

 gredients. 



From this period, the importance of the fubjecl being 

 fully ellablilhtd, tables were multiplied and the general 

 fyllem of affinity was invelligated by fome of the ablell 

 chemills of the age, among whom the names of Erxlcben 

 and Weigleb Hand eminently dillinguilhed. At length, in 

 1775, the illullrious Bergman publilhed his diffcrtation on 

 eleclive attractions, in the tranfaclions of the Royal Society 

 of Upfal, and fucceffive editions of his tables made their 

 appearance in 1779 and 1783. Thefe tables may jullly be 

 confidered as a mallerpiece of Ikill and indutlry ; the 

 affinities of no lefs than 59 fubllances are afcertained with 

 gitat exaclnefs, and the dillindlion between thofe that take 

 place in the inoill and dry way is precifely Hated : the 

 method of regiltering cafes of compound affinity is per- 

 fected, and 64 of the mofl important are added to the ge- 

 neral Hock of chemical fcience. Since the death of Berg~ 

 man, fucceffive impreffions of his tables have appeared with, 

 little or no alteration, till Dr. Pearfon's in 1799. In this, 

 the nomenclature is changed, and in part reformed accord- 

 ing to the French fyfttm, a few articles to be found irk 



Bergman. 



