A F F 



proportion as its furfaccs art multiplied by grinding it do'.vn 

 to powder, fo in its altradlion of agi!;rt'^atiiin diminillicd ; 

 and the adioii of tlio fulphuric acid on the lime, to the ex. 

 cUilion of the tliioHo atid, bcconirs nioif energetic. It 

 would be more corrett to fay, that the ifficncy of chemical 

 atriuity is inverftly as tlic attraftiim of iigsjrcgation ; bc- 

 taufe its .iWoliUc force remains coulhuitly the fame, and it 

 only appc ars to iiicreaftf on account of the diminution of its 

 an'.agonilS attraCition. Thus, let the chemical affinity of lime 

 and fluoric acid be = ic, and the force of its coheiivc ?.t- 

 tradion, wheli cryllallized = 6, the fnm of its quiefcent 

 alRnities will be = 16. Let the affinity of fulphuric acid 

 for lime, or the divellent affinity be := 13 ; it is obvious 

 that no decompofition cati take place, aliliough the chemi- 

 cal divellent affinity is fupcrior to the quiefcent one ; but, 

 thefc continuing the fame, let the attraction of aggregation 

 be reduced by mechaniciJ triture to be only = 2, then the 

 ftrongtll chemical affinity will become efficacious, and a de- 

 compofition will take place. 



The aggregation of bodies is, however, more frequently 

 overcome by the aftion oi fokition by water, or fufion by 

 fire, and tb.efe menllrua arc fo commonly made ufe of that 

 the habit is infenfibly acquired of coufuicring folutions of 

 fubihinces in water or fire, as equally limple with the iame 

 bodies when in a concrete Hate. It is from this overlight 

 tliat all the apparent exceptions to this law have originated. 

 " If, fays Morveau, we apply heat to a mixture of acid 

 «' and water, or of alcohol and water, v/hich are real chemi- 

 " c;J combinations, we only augment the degree of their 

 " rarefaftlon ; but inllead of thus promoting their union we 

 " fcparate them ; the fame is the cafe with thofe metallic 

 " oxyds that are decompofable by mere heat, and of all 

 " thofe co;npound falts, one of the principles of which is 

 " more fixed than the other." It, however, caloric is capa- 

 ble of being exhibited in an uncombined Itate, and of being 

 diilinguiflied from all other fubftances by peculiar fenfihle 

 pi-opcrties, if thefe are modified and changed by combina- 

 tion v/jth different bodies, if caloric may be transfeired 

 from one body to another, according to an afcertaincd or- 

 der of chemical affinity ; and finally, if it may be feparated 

 from its combination, and again exhibited with all the ori- 

 ginal properties that were at firft charafteriftic of it, what 

 rcafon is there to deny that it is fo far a material fubflance, 

 as to be capable of chemical combination ? To recur, there- 

 fore, to the examples adduced by Morveau : if to the com- 

 pound of alcohol and water a certain quantity of caloric be 

 added, it wiU be divided between the two ingredients, ac- 

 cording to their refpective affinities, and in proportion to 

 the addition of this new fubllance will the original affinities 

 of the water and alcohol be weakened : the alcohol being 

 the fooneft faturated with caloric, will afTume a gaffeous 

 form, and being afiiiled by the attraction of gravitation, 

 will fcparate from the water. In all this there is nothing 

 inconfiilent with the general order of chemical agency ; 

 whereas the realoning of Morveau involves a contradiction 

 in terms : for if the force of chemical affinity is capable of 

 being overcome by rarefaction, and if rarefa&ion is no- 

 tiinig but the greateft poffible refolution of an aegregate, 

 it follows that the abfohite force of chemical affinity may 

 be overcome by the negation of the attraftion of aggrega- 

 tion. 



7, IVh^n iiuo or more fiibjlances uiijte to form a chemiml 

 compound, th.'y lofe their otun peculiar properties, and' thufe of 

 theneiu compound are r.ot to be inferred from the propertief of its 

 elements. 



It is not meant by this, that the properties of a com- 



A F F 



pound are always, and in every particular different front 

 thoie of its conlUtuent parts, only that they arc by no 

 means intern. ediate between them. Tlie reverie of this 

 was maintained by the earlier chemiRs, and accordingly 

 Slahl taught that falts were compofed of earth and water, 

 becaufe he fancied their properties to be a medium between 

 thofe of thefe two fubllances. It will probably be thought 

 at present that the ver)' inllance which Stahl has felected to 

 prove his maxim is rather conclufive on the contrary fide ; 

 but niunbeilefs other more unexceptionable examples occur 

 in cverv department of chemillr)-. Tin and iron arc both 

 of them very duftile, but if equal parts of the two are 

 melted together, the refiilt is a brittle alloy. Magnefia is 

 tallelefs, fulphuric acid is intenl'ely four, con\bine them, and 

 we obtain a bitter fait. Alkali is colourlcfs, fynip of vio- 

 lets is purple, the produft upon mixture is green ; carbo- 

 nic acid and amiuoni'., when fcparate, are gafieous, mix. 

 them, and they become folid. Amalgam of lead, and of 

 bifnuith are folid, by combination they form a liquid. 



8. The capacity for caloric is akvays changed Ly chemical 

 combination. 



This law is, in faft, only an offset from the preceding ; 

 and for the explanation of it, fee caloric. 



§ VI. Anomalies. 



All thofe cafes of chemical affinity, which either really 

 or apparently contradift the general laws that have juil 

 been cited, may be reduced to two claffes ; -viz. thofe 

 depending on the variable force of afihiity itfclf, and' 

 thofe occafioned by the aftion of other antagonill attrac- 

 tions. 



I . The whole fyftem of Bergman depends on the abfo- 

 lute uniformity of eletlive attrattion, on its lieing a conllant 

 force, fo that if (the temperature and menftmum remaining 

 the fame) the combination A B is deconipofed by C, to 

 the exclufion of B, the new fubilance A C, cannot b^ 

 again feparated by B, fo as to reproduce A B, and leave 

 C at liberty. With Hill more rigour does this apply to all 

 the methods of eftimating numerically the excefs of one 

 affinity over another, independently of the relative quanti. 

 ties of the fubftances employed. It appears, neverlhelefs,. 

 from BerthoUct's treatife on this fubjcd, that in almoft all 

 cafes of change produced by elective affinity, there is not 

 a total transfer of the bafe, but a partition of it betweeu- 

 the two oppofite attracting fubllances in a compound ratio- 

 of the relative force of affinity and quantity of each. That 

 in many cafes the excefs of quantity may fupply the defi- 

 ciency of force, and therefore that the raafs mufl be care- 

 fully taken into conilderation, together with the fpecific 

 force in the conftruction of tables of affinity. Barytes is 

 properly placed by Bergman at the head of the column of the 

 affinities of fulphuric acid, in water ; not however becaufe it 

 is impoffiblc for fulphat of baiytes to be decompofe(» by 

 any other fubftanec, but becaufe, if equal quantitiss are 

 taken of all the fubftances that combine with fulphuric 

 acid, barytes will be found to dec* mpofe the greatell pro- 

 portion of any other fulphat ; and of the fulphat of barytes 

 the largtft part will remain iindecompofed by a quantity of 

 any body equal in weight to the barytic part of the fait in 

 qucRion. Thus, if equal parts of pure potalh and fulphat of 

 barytes are boiled together to drynefo in a fmall quantity 

 of water, it will be found that the fulphunc acid has been 

 divided between the two bales in the compound ratio of 

 their mafs and their force of affinity ; the greater part of 

 the barytic fulphat will be found undecompofed, a fmall 

 quantity of barytes* will be fouiid at liberty, moll of the 



potath 



