LIQJJIDITY. 



Sir Ifaac Newton and the philofophers of his time fiip- 

 pofed, that fluidity was occafioned by the fpherical form of 

 the particles of the bodies by which they were fuppofed to 

 move with facility in all direftions. Since, however, the 

 conftitiition of bodies in different Itates is better under- 

 ilood, fuch an hypothefis is not neceflary. Haiiy has ren- 

 dered it very probable, that the particles of bodies are of 

 the form of their primitive cryftals, which are flat-fided 

 folids of the fame regular form. 



When we recoUetl that the particles of bodies, in the 

 moft folid ftate in which we find them, are far from touching 

 each other, their fpherical figure would not avail in giving 

 them fluid properties, when they are changed into that form 

 by the agency of heat. 



Since bodies are found to expand by heat, and contraft 

 when the heat is withdrawn, it feems obvious, that the 

 particles of bodies are afted upon by two forces ; the one 

 attraftion, refiding in the particles of the bodies ; and the 

 other, the repuliion of the particles of caloric for each ; and 

 which being combined with the attraftive particles, give 

 them the tendency to recede from each other, at the fame 

 time that the attraction is not altered. 



The eqnihbrium, between the two forces, is kept up by 

 the different diftances of the particles, on which the relative 

 volumes belonging to different temperatures depend. If 

 we gradually raife a rod of tin, or any other metal, from 

 the common temperature to its fufmg point, we firft ob- 

 ferve its progrefSve expanfion, by which we are to infer, 

 that the coheiive force is diminifliing in fome ratio of the 

 expanfion. When it has 'arrived at a certain temperature, 

 the pillar of metal will lofe its form, and if it were not 

 confined by the fides, it would become extended into a flieet 

 of a thicknefs proportionate to its degree of fluidity. In 

 Other words, when the cohefion of the particles is fo dimi- 

 niflied, as to be exceeded by the atlion of gravity upon the 

 particles individually, the folid will affume the liquid form. 

 This hypothesis perfetlly explains all the phenomena at- 

 tendant on the liquefadion of thofe bodies which are not 

 fufceptible of cryllallization, fuch as wax, refin, tallow, 

 and feveral other fubftances. Such bodies, we obferve, firft 

 begin to foften by the partial lofs of cohefion, and gra- 

 dually become more and more liquid, till tlie degree nf the 

 heat fliall occafion their deconipofition, or give them the 

 elaftic form. 



Thefe bodies, as we (hould expeft, increafe in volume to 

 the point of extreme liquidity, and the fohd mafs is of much 

 greater fpecific gravity than the liquid. 



The clafs of bodies that ■ are fufceptible of the cryf- 

 talline form, which takes place at the point of liquidity, 

 appears to depend upon fome other caufe than the mere 

 prefence of caloric, and on that account will prefent many 

 anomalies to the above theory. Thefe anomalies, however, 

 are alone obvious at the point when cryftallization is taking 

 place. In fome of thefe bodies, fuch as water, we do not 

 obferve any medium between perfeA folidity and almoft per- 

 feft liquidity. 



The folids are in general of lefs fpecific gravity th^n the 

 liquids, and confequently float upon them. And it is ob- 

 ferved, that the point of maximum denfity is at a higher 

 temperature than the point of congelation. The greateft 

 denfity of water is, according to the enquiries of Dalton, 

 at ^6 , the point of congelation being at 32°. If, however, 

 a mafs of water be cooled, while the veflel holding it be 

 kept at reR, it may be reduced as low as 18 , and even 16 , 

 without congelation, contrafting in volume all the time. 

 When, however, the veflel is agitated by giving a tremulous 

 Jnotion to the table, the whole becomes inftantly folid, with 



a certain degree of expanfion, and the temperature rifes tc 

 32^ at the fame moment of time. It would therefore feem, 

 that the contraction and expanfion by the prefence or ab-- 

 fence of caloric would be perfeftly confonant with the chapge 

 of temperature, were it not for the interference of this myf- 

 terious law of cryftallization. 



'I'he circijmftances under which the congelation of cryf- 

 talhnc bodies takes place, clearly fliews that fomething more 

 is wanting than the mere abftraftion of caloric. Salts are 

 found to cryftallize by ftanding for a certain time, although 

 the temperature and quantity of water remain the fame. It 

 would therefore appear, that the integrant particles re- 

 quire time to arrange themfelves ; and that the falted form, 

 as well as their regular form, is dependent on their arrange- 

 ment : or that attraftion of aggregation is the greateft 

 when the integrant particles are placed in one particular 

 direftion. And it appears, fince the ftrongeft aggregation 

 exifts when the cryftals are beft formed, that the attraftion 

 caufing folidity is the greateft when the homologous fides of 

 the particles are parallel to one another, taking it for granted, 

 that the particles are of the form of the primitive cryftal. 



The idea of a polarity in the particles of bodies is not 

 new ; and, from many recent fadls, does not appear very 

 gratuitous. Bodies which are magnetic or eleftrical, 

 appear to be capable of arranging themfelves in fuch order, 

 that their poles fliall be reverfed to each other, from the 

 attraftions of oppofite poles. We have already a ftriking 

 inftance of this eleftrical polarity in cryftals of the tour- 

 nuilin. And from fome late experiments by Malus, it ap- 

 pears that even the particles of light are pofleffed of 

 polarity, confirming what Newton had before conjectured. 



When we apply heat to a folid cryftalline body, fuch as 

 a piece of ice, caloric does not effeft its hquefaftion by re- 

 moving its particles to a greater diftance, becaufe the ice is 

 not fo denfe as the water ; confequently, the particles are 

 nearer in the liquid than in the folid form. It would ap- 

 pear, in this inftance, that the caloric had the power of lef- 

 fening, and perhaps deftroying altogether, the polarity of 

 the particles, an effeft which is not more unlikely than that 

 of a certain temperature deftroying the polarity of a magnet. 

 When, however, the caloric is removed, the polarity may 

 return, but this alone is not fufficient to render the water 

 lolid. A certain time, with a certain degree of agitation, 

 is neceffary to allow the particles to affume their moft 

 favourable pofition for conftituting the greateft aggregation, 

 and their greateft Regularity. We alfo fliould infer, that 

 during this change, in which much force is exerted, the 

 particles occupy more fpace, by which the expanfion is 

 occafioned. Similar effefts take place in the congelation 

 of moft of the metals ; and it will, doubtlefs, be found, that 

 the folids of" all bodies will be of lefs fpecific gravity than 

 their reipeftive liquids, in proportijn to the fufceptibility of 

 cryftallization, or, if we may be allowed the expreffion, as 

 the polar force of their panicles. 



The particles of thofe bodies which are not fufceptible 

 of cr)'ftallization may have little or no polarity, and hence 

 may owe their fohdification to the mere abfcnce of caloric. 

 Their tranfition from the folid to the liquid form will be 

 gradual and flow, and their hardnefs will be iuverfely as the 

 caloric they contain. This is not the cafe with cryftalline 

 bodies ; their tranfition from the liquid to the folid form 

 is governed by feveral circumftances, and their hardnefs is 

 not immediately in the inverfe ratio of their caloric, but 

 more dependent upon their polar arrangement. In all pro- 

 bability, if it were not tor this latter caufe, the point of 

 congelation would be much lower in the thermometrical 

 fcale. What we termed confufed cryftallization, may be 

 9 a ftate 



