A F r 



potafh will alfo be uncomhiiied, but a certain proportion 

 will be imited with tlie fulphuric acid wliicli the barytes 

 has lotl, in the form of fnlphat of potafli. To make this 

 matter plainL'r, kt us exsniiue the rclults of the decompofi- 

 tion of iulphat of barj'tea by potalli, aud of iulpliat of pot- 

 afli by barytes, as calculated from Mr. Kirwau's data, bul- 

 phnt of barytes contains 3.33 parts ot lulphuric acid and 

 6.66 of barytes : it thereiore we take ten paits of this 

 fait and an equal quantity of potafli we have, 



3. 33 fulph. a. 

 6. 66 barytes 



10. pota(h. 

 and the affinity of equal parts of barytes and potafli for 

 fulphuric acid being : 2 : 1.2 1 the acid, if Ihared between 

 them in the compound ratio of their niafs and their affinity, 

 will be 13.32 to barytes, and 12. 1 to potafli: now the 

 coniiwlition of fulphat of barytes beins^ as already Hated, 

 and that of fulphal of potafh being 54 of alkali to 'I J of 

 acid, there will remain undecompoicd 5.22 parts of barytic 

 fnlphat; 5.18 of barytea will be fet at liberty; 3.47 of 

 fulphated potafli will be produced, and y.ll of potalh will 

 continue uncombined. If, on the other hand, we mix equal 

 parts of fulphat of potafli and batytes we fliall have 

 5. 48 potafli 



4. 52 i'ulph. a. 

 10. barytes 



and the acid being divided between the bafes in tne com- 

 pound ratio of their niaffes and force of affinity, will give 

 6.63 parts to the potaih and 20. to the bai-ytes : there will 

 then be 2.48 parts fulphat of potafh remaining undecom- 

 pofed,and 3.24 baiytes uncombined; 4. 12 parts potafh will be 

 fet at liberty, and 10.14 fnlphat of barytes will be produced. 



It is not merely in a few ini^aiices that this partition of 

 one body between two others, according to their refpeftive 

 maffes and affinities, takes place, there being fcarcely any 

 example to the contrary. Lime has a weaker affinity than 

 potafh for fulphuric acid ; yet lime, when afting on an equal 

 weight of fulphat of potafli, is capable of partly deconi- 

 pofing it : the fame happens with phofphat of lime and 

 potafli, with fulphat of potafhand foda, &c. 



From thefe and fimilar experiments it follows, that when 

 a compound of two fubflanccs is atted on by any third 

 body, that part of the compound which is the fnbjctl of 

 combination, is fliared between the two remaining elements, 

 not only in the proportion of their refpeftive degrees of 

 affinity, but alfo according to their quantity ; thefe two 

 fubflances therefore mufl: be confidered as oppofite forces, 

 dividing between them the fubjeft of combination, accord- 

 ing to the ratio of their intenfity, and this intenfity depends, 

 not only on the energy of affinity, but alfo on the quan- 

 tity, fo that by varying this in cither, the effeft produced 

 will be proportionably modified. 



Another confequence is, that the aftion of a fubftance 

 in oppofition to any particular combination decreafes, as it 

 advances towards faturation ; and as the force of this is 

 continually diminifhing, fo the power of the fubftance 

 eliminated is enlarging according to its increafed quantity, 

 and this efTeft takes place till the antagonifl forces txaftly 

 countei-polfe each other. 



A third inference is, that in cafes of precipitation the preci- 

 pitate neceffarily retains a portion of the iubflance with which 

 it had before been combined ; for during the inftant of this 

 aftion, a partition is made of the fubject of combination in 

 proportion to the affinities and maffes of the fubftances em- 

 ployed, 



2. The variable ratio of the force of affinity between 

 the two elements of particular coi?ipounds, is another ano- 



A F F 



maly and occafional fource of error. Thus the black oxyd 

 of mangancfe readily parts with a portion of its oxygen, 

 by the aftion of fucii a portion of caloric as will juft niife 

 it to ignition ; but after it has parted with this excefs of 

 oxygen, the aOFinity which unites it to the remainder, fol- 

 lows a Ir.uch higiier ratio, fo that the ntmofl poffiblc ac- 

 cumulation of caloric is unable to produce any further de- 

 compofluon : hence the affinity of metallic mangancfe for 

 oxygen is reiy high, and the affinity of tlie wliite oxyd 

 ot mangancfe for oxygen is much lower than it ought to 

 be, provided the affinity of thefe two fubftances was in an 

 uniform ratio, according to their relative proportions. So 

 again, the acidulous fulplmt of barytes is deconipofcd by 

 nn equal quantity of water into the common barytic ful- 

 phat and fulphuric acid, yet no addition of water can pro- 

 duce any further decompofition of this earthy fait ; tlie 

 general tac't, therefore, of mafs compenfating for inferiority 

 of attractive force does not here hold good. Another 

 flriking example of the fame is the decompofition of tar- 

 trite of potafh by acetous acid, into acidulous tartrite of 

 potafli and acetite of potalh ; and the refift:ance made by the 

 acidulous tartrite to all further decompofition by any quantity 

 of acetous acid. The fame may be faid of the affinity of mu- 

 riatic acid to oxygen, and of its bafe for the fame fubftance. 



3. The order of chemical affinities is often modified 

 by the attraftion of faline vegetation, a power belonging to 

 all but the dehqucfcent falts, which caufes them to feparate 

 from the water that holds them in folution, and rife in the 

 form of vegetations up the fide; of the veflel in which they 

 are contained ; the efflorcfcent falts are more particularlv- 

 fubject to this attraftion, and confequently their affinities 

 are the moft frequently dlflurbed by this force. Muriat 

 of foda is fcarcely, if at all, decompofed by carbonated lime 

 in water; but if, according to Scheele's procefs, hnie and mu- 

 riat of foda are mixed witli only fo much water as will make 

 the mafs into a parte, and this is expofed to carbonic acid 

 gas, a faline efllorefcence will fliortly make its appearance, 

 poffcfling all the properties of carbonated foda, and the. 

 muriat of lime in a deliquefcent flate will be found at the 

 bottom of the veflel : but if the carbonat of foda is dif- 

 folved and added to the muriat of lime, an immediate de- 

 compofition will take place, and carbonated hme and mu- 

 riat of foda will be produced. A fimilar cfleft happens 

 when iron is moiftened with muriat of foda and expofed to 

 carbonic acid gas. 



4. The laft caufe of anomaly that need be mentioned, 

 arifes from the affinity of water with fubftances diffolved in 

 it, and this is a very important circumilancc to be aware of, 

 as it accounts for the otherwife inexphcable phenomenon of 

 what are called wcompat'ilk falts in certain mineral waters. 

 Bergman, Kirwan, Cavendifti, and other eminent chemifts, 

 have difcovered in mineral waters the co-exiftence of fmall 

 quantities of various falts, which, in common circumftancet^, 

 deconipofe each other; thus the waters of Rathbone-placc, 

 according to Cavendifh, contain in the pint 0.9 of a grain ' 

 carbonated ammonia, and 1.2 grains of fiflphat of lime. 

 A gallon ot Harrowgate water contains 13 grains niuriated 

 lime, and 5 grains fulphated magnefia. But in both thefe 

 cafes, on account of the fmall quantity of fait compared to 

 that of the water, the affinity of this laft, aided by its mafs, 

 is capable of overcoming the excefs of the divellent, over 

 the qulefccnt afrinitics of the falts that it holds in folution ; 

 and is obvioufly the truereafon of the fatt, for if, by e\a- 

 poration, a confiderable proportion of the water is taken 

 away, the divellent affinities of the two falts become effica- 

 cious, and decompofition takes place. 



For other fubjeds in fome meafure conncAcd with the 

 Z z 2 important 



