A D H 



A D II 



Achard ronned the following Table of the adhcfiv* forae of 

 a glafs dilk, 1 1 inch in diameter, to water at different tem- 

 peraturci. 



TABLE I. 



Of the accuracy of this Table of M. Achard's there feems 

 no reaion to doubt, fmce, in the individual inilances, the dif- 

 ference between the force of adhefion found by e.-^periment, 

 and that afcertsined by calculation, is fo confiderable as to 

 exclude the idea of fiAion; while, upon the general average, 

 the diiference is fo fmall as to give a high opinion of the 

 precillon with which the enquiry has been condutlcd. 



We learn from this Table, that for every degree of Sulzer's 

 thermometer ( i.i565Fahren.) taken in adefcending feries,the 

 force with which a gbfs difl': 1.5 inches in diameter adheres to 

 the furface of water, is increaicd by 0.1876 grains according 

 to calculation, or 0.1858 by experiment, in an uniform 

 ratio : now two things take place during the coohng of the 

 water, viz. a portion of caloric is feparated, and the bulk 

 of the water is leffened : each of thefe caufes may account 

 for the increafed adhefive force, but upon different pnnciples. 

 If it is owing to the cfcape of caloric, it may be accounted for 

 in the following way. Water at any tlate of liquidity is, pro- 

 perly fpeaking, a compound of caloric and water, which 

 combine together by a flight degree of affinity ; and in pro- 

 portion to this force refill the union of any third fubftance 

 either with the caloric or the water : if part of the caloric is 

 taken away, the water is more difpofed to union with a third 

 fubftance by the whole quiefcent affinity of the water and the 

 abftradled caloric ; therefore the force by which a plate of 



glafj adheres to water is increafed, exactly in proportion to 

 the diminution of the temperature, or, in oilier wordj, tlie 

 increafc of weight is the exponent of the quiefcent alfinity 

 between the mafs of water and the calorie taken away. Ac- 

 cording toMon-eau'aobfervationson this fame Table ; " The 

 " adhefion is ftronger whtiv the water is colder, becaufc 

 " containing more ponderable matter in a given volume, it 

 " prefents to 'the glafs-plate more points of contafl ; and 

 " the force of adhefion being proportional to the futn of 

 " thefe points, it ought to augment or diminiPi, asthelluid 

 " is condenfed by cold, or rarefied by heat." Tliife few- 

 words exprefs the aim and objeifl of all the experiments of 

 Morveau on this fubieCt ; namely, that chemical affiiiitv is 

 only a modification of the attraction ofcohefion, and in like 

 manner fubjedt to mathematical computation. The general 

 reafonings on which this opinion is founded will be diicuffed 

 hereafter in the article chem'ual affinity ; all that is nccef- 

 fary here, is to flicw, that the argument juft mentioned, de- 

 duced from M. Achard's Table, is liable to a very llrong oh- 

 jedion. The fadl being allowed, that the adhefion ber jme« 

 uniformly greater in proportion to the diminidied tempera- 

 ture of the water, it follows, that if this adhefion is owing 

 fiinply to the cohefive altraftion of the proximate particles ot 

 the glafs and water, the degree of this force will be accord- 

 ing to the number of proximate particles in a given fuper- 

 ficies ; or, in otlier words, dirciitly as the fpecific gravity. 

 Now, by the experiments of Achard, the adhefion Ijetweeii 

 the glafs-plate and water at 152° Fahren. is equal to 80 

 grains, and at 96° Fahr. equal to 89 grains. From Kir- 

 wan's experiments on fpecific gravity (Phil. Tranf. vol. Ixxv. 

 pt. 1. p. 267.) it appears, that the weight of a cubic inch 

 of water at 152'' Fahr. is equal to 248.7 grains; and the 

 fiime at 96 Fahr. equal, to 252.47 grs. ; if, therefore, the 

 adhefion is as the fpecific gravity, the adhefive force at 

 96 Fahr. ought to be only 81.21, inllead of 89. for 



248.7 : 80 : : 252.47 : 81.21 . 

 Having afccitained the influence of temperature on tlie ad- 

 hefion of furfaces, the next objeft with M. Achard was to 

 detemiine the ratio between the force of adhefion and the 

 fuperficial magnitude of the folid. For this purpofe he pro- 

 cured round plates of glafs of different diameters, from 

 1.5 inch to 7 inches, and havhig firfl. determined the 

 force of their adhefion with the different fluids, by the 

 number of grains neceffary to overcome it, he afterivards 

 calculated the fame by the following equation. Let /> be 

 the force of adhefion belonging to a dilk of glafs, wliofe 

 diameter is a ; and y the adhefive force of a fimilar dilk, 

 whofe diameter is b, we fliall then have «' : i' : '• p • y i 



and V = . 



■^ a' 



From thefe materials the following Table has been cou« 



Umaed. 



VoL.L 



Ff 



TABLE 



