A D II 



A D H 



H'lhefion ill prefence of the Dijon academy, (Joum dc Pliy- 

 fiqiii;, i. p. 172 aiul 41^0.) ck'inoiilliating, as indeed Hniikf- 

 bee iiad done before iiim, not only tluit water alcends be- 

 tween two parallel plates of tallmv fepavatcd from each other 

 f of a line, but alio that the atmofpheric prefluie is not in 

 the lead decree the caule of the phenomenon, whieli is folely 

 attributable to attraelion : in proof of this, a pollflied dil1< of 

 glafs, 30 lines in diameter, was fufpended to the arm of a 

 balance, and brought into contatl with a furface of mer- 

 cury ; the countcrpoife required to feparate it was equivalent 

 to 9 gros, and a few grains, and upon moving the apparatus 

 into the -receiver of an air-pump, and forming as perfect a 

 vacuum as pofiible, precil'ely the fame couiUeipoife was re- 

 quired as before. 



In the profecution of his inquiries on this fubjeCt, which 

 hitherto had pnncipally interelled the mathematical jjhilo- 

 fophers, Morveau was led to difcoveries, wiiich promiled at 

 firll to reduce the intricate fcience of chemical affinities to 

 the certainty of algebraic computation ; and, if that hope 

 has fince been deceived, it Hill remains an intereiling objeft 

 to the chemift, and affords much fubfidiary afTillancc in the 

 inveftigation of the general laws of chemical agef.cy. 



He obferved, that the fame dilk of glafs which, when in 

 contatl with pure water, adhered to it with a force ctpial to 

 2j8 grains, required a countcrpoife of only 210, in order to 

 feparate it from a folution of potafli, notwithftanding the fu- 

 pei-ior denfily of this lad. This inequality of effefts on 

 equal diameters, and in an invcrfe order to that of the re- 

 fpecflive fpecific gravities of the two fluids, appeared not 

 only to be decifive in favour of Dr. Taylor's method, but 

 to encourage the hope of applying it to the calculation of 

 chemical affinities. 



In order to verifv this propofition f Elcmens de Chym'e. 

 de I'Acadcmie do Dijon, vol. i. p. 63.) plates of the difTe- 

 rent metals in their higheft flate of purity were procured, 

 perfectly round, an inch in diameter, of the fame thicknefs, 

 well poliihed, and furaiflicd with a fmall ring in the centre of 

 each fo as to keep them lufpended pvecifely parallel to tlie 

 plane of the horizon. Each of thefe plates was in turn 

 fufpended to the anri of an alfay balance, and exaclly coun- 

 terpoifed by weights placed in the fcale attached to the 

 oppofite arm ; the plate thus balanced was applied to the 

 furface of fome mercuiy in a cup about two lines beneath 

 it, by Aiding the plate over the mercury as in the filvering 

 of mirrors, fo as to exclude every bubble of air, weights 

 were then fucccfiively added till the adhefion between tlie 

 plate and mercury was broken. Frelh mercury was ufed 

 for each experiment. The following is the Table of refults. 

 Gold adheres to mercury with a force equal to 44.6 grains. 

 Silver - ■. - 429 



Tin - - - 418 



Lead - - - 397 



. Bifmuth - - - 372 



Zinc - - - 204 



Copper - - - 142 



Antimony (regulus) - - 126 



Iron - - - 115 



Cobalt ... 8 



The Pcriking differences in the above Tabic fhew that the 

 prefTure of the atmcfphere has no (hare in them, fince in 

 this refpeft the circumftances of each were precifely fimilar : 

 nor do they depend on the refpeflive fpecific gravities ; for 

 if fo, filver fhould rank after lead, cobalt before zinc, and 

 iron before tin. The only order which agrees with the 

 above is that of the chemical affinity of thefe metals, or the 

 rcfpedlive degrees of their folubility in mercury (See amal- 



gam! : it is highly probable, therefore, that at leall the 

 principal part or the adhefive force thus found by experi- 

 ment is owing to chemical alfinity, and that the above nu- 

 merical feries 446, 429, 418, 397, &c. is an apprcximation 

 towards the ratio of the relative aflinities of gold, filvcr, tin, 

 lead, See. for mercury. 



M. Achard, of Berlin, convinced by Morveau's difcoveries 

 of the accuracy of Dr. Taylor's iriethod, toUov.'cd them up 

 by a great multitude of experiments which were publiOied. 

 in 1780, along with other trafts in his Chym!j'r/.i Pls^J'iche 

 fchnp.en. Tlie rehilts of thefe, if accurate, would make a 

 conliderablc aceellion to the fcience of cheir.ical philofophy, 

 but as there are tome rather fufpicious circumllances, it 

 will be UeCL-fTaiy to inveibgate M. Achard's lyllem with 

 fome minutenefs. 



He lays down three conditions as efFentir.! to the accuracy 

 of each experiment. I. Tliat the iclid, whole adhefion with 

 the fluid is to be afcertaiued, fliould be fufpended by its 

 true central point, in order to be in a truly hori/onval po- 

 fition, and that the force employed to feparate the adhefion 

 fliould always form a right ar:gle with the fluid. 2. That 

 no air bubble fliould remain interpofed between the folid 

 and fluid ; which is eafily perceived when ufing dlfks of 

 glafa, but can only be inferred when ulir.g opaque folids ; 

 to obviate this caufe of inaccuracy he has found no method 

 an'wer fo well iis Aiding the plates on the furface of the 

 PiUid as explained above. 3. In adding the counttrpoife, 

 elpecially towards the end, care mu ft be _ taken to ufc very 

 fmall weights, fuch as pieces of paper, a quarter of a grain 

 each, and to place thefe in the fcale, gently and gradu:Jly, fo 

 as to avoid any jerk or fuddcn action. 



The lirft point to be afcertaiued was, -whether tlie tem- 

 perature remaining the fame, the difference of atmofpherical 

 prefiure, as evinced by the barometer, had any influence on 

 the adhefion of furfaces.; he found that in this refpecl there 

 was no difi'ererice in the adhefive force between a plate of 

 glafs and dlfliUed water. 



The refults were, b.owever, no longer tjniform, when ha 

 operated at different temperatures with the fame elevation 

 of the barometer, nor did this variation arife from the 

 different temperatures of the furrounding air, bat folely 

 from that of the water : purfuing this train of experiment 

 he found that the adlicfiou of folids to fluids is conflantly in 

 an inverfc ratio to tlieir temperature : and for the verilica- 

 tion of his experiments he inftituted a number of calcula- 

 tions from the following data. Let s be the temperature 

 of the water ; y, the correfpanding adhefion ; h, its co-effi- 

 cient ; and a the conltant force ; hence we have the equa- 

 tion x:=a — hy. To find the value of a and 3 he made 

 ule of two experiments, the one in which water at, 104° of 

 Sulzer's thermometer (152°. 278 Fahrenheit) adhered to 

 the glafs difk with a force equal to 80 grains, the other 

 where water at 56° S. (96^. 764 Fahrenheit) adhered with 

 a force equal to 89 grains. Proceeding from thefe two 

 terms 104=1; — 80 3 

 56=:(Z— 89 b 



we have, n = 530 



3=-ili 



Hence the relation of the temperature of the water to its 

 adhefion to the glafs, may be thus expreffed, .v=530 — V J* » 

 and from this are deduced the correfponding values of 

 .V and y for all the adhefions of glafs to water at any tem- 



perature. 



From thefe data. 



and the correfponding experiments, M. 



Achard 



