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That a folid may be diflolved in a fluid, it is neceffary 

 that the force of affinity between the two (hould be fuffi- 

 cient to overcome the force of cohefion between the particles 

 of the folid ; and hence it is, that Iieat fo much affilts iolu- 

 tion by lellening the force of cohefion between all particles 

 of matter. 



M. Gellert, liowever, reprefents as folvents, the bodies 

 which are generally confidered as diflolved, and hence, he 

 fays, that fand difl'blves alkali. If, indeed, we allow the 

 aftion of the combining bodies to be mutual, it fignifies 

 little which we call the folvent, and which the body dif- 

 folved ; though it feems more clear and accurate to call that 

 body the folvent, whofe integrant parts are already fepa- 

 rated before the folution, and that the body diflolved, 

 whofe integrant parts are only difunited during the att of 

 folution. The folution of bodies may be eff'efted either 

 by the humid, or by the dry way ; of the former kind are 

 thofe folutions, in which the integrant parts of one or both 

 of the two bodies are diftributed in an aqueous fluid, e. g. 

 of acids ; and thofe folutions, in which one or both bodies 

 are rendered fluid by fire, as in vitrification, and in alloys 

 of metals with each other, are of the latter kind. A per- 

 fect folution requires, that each of the integrant parts of 

 one body be united to one of the integrant parts of an- 

 other : hence, if one of them be tranfparent, we ought to 

 have, after the mutual folution, a tranfparent compound, 

 fuch as occurs in the folutions of calcareous ftones and acids, 

 and thofe of earths by alkalies : whereas the folution of 

 foap in water is incomplete ; and the fame may be faid of 

 glafles that are not perfcftly tranfparent. 



As the folution of two bodies can only be efFefted by the 

 mutual attraction of their parts to each other, thefe parts, 

 after the folution, are found to adhere together : fo that 

 heavy bodies, e. g. corrofive fublimate, may be fufpended 

 in the thinneft and lightell liquids, e. g. fpirit of wine, 

 when they are truly diflolved by each other. 



In all cafes of folution at a common temperature, it 

 generally happens, that the mixture in the aft of folution 

 becomes either warmer or colder than the ingredients were 

 before the mixture. This is owing to an evolution or ab- 

 forption of free caloric, from the mixtures having a lefs or 

 greater capacity for caloric, than the mean capacity of the 

 two fubftances taken feparately. See Cilgric. 



It happens alfo, in the greater number of cafes of folu- 

 tion, that the mixture has a greater fpecific gravity than 

 the mean gravity of the ingredients, relatively to their re- 

 fpeftive quantities. Hence they occupy lefs fpace than be- 

 fore, which may be feen by putti;ig into a bottle any foluble 

 fait [e. g. fulphate of foda), and filling it to the brim with 

 water ; after the folution is effefted, the liquor will appear 

 to have funk through a certain interval below the firft level, 

 without any lofs of the ingredients. See Affinity. 



When folutions of falts are congealed, the ice often af- 

 fords very pretty figures ; but it is to be obferved, that the 

 fame fait does not always give the fame figures. Thus, 

 the fame folution of verdigris, frozen by means of fno.v 

 and fait, affords a different figure, from what is produced 

 by the natural cold of the air. And the former ice being 

 tha-.ved, and left to freeze in the fame phial, did not give the 

 fame figures as at firil. See Boyle's Works Abridged, 

 p. i68. 



Solution, in Metallurgy, is dirtinguiflied into dry and 

 moill. The dry folution is the blending imperceptibly a 

 fmall quantity of a metal or mineral, with a very large one 

 of fome other body, dry, liard, and not fluid when cold. 

 The moifl fcJution is the diftributing a body tliroogh the 



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very minuteft parts of an aqueous, or in great part aque- 

 ous fluid, in fuch manner, that both may turn into a fluid, 

 to appearance homogeneous, which goes through all filters, 

 without being detained or feparated by them, and the 

 fmalleft part of which contains in it a proportionable quao- 

 tity of both the meuftruum or difiolvent, and of the dif- 

 folved body. The folution of gold in aqua regia, and of 

 filver in aqua fortis, as alfo that of any of the falts in water, 

 are folutions of this kind. Cramer's Art of Aflaying, 

 p. 194. 



In the making of the feveral metallic refolutions, for the 

 neceflary procefles in chemiltry, the operator is fubjeft to 

 great danger in his health, from the noxious vapours. This 

 has been an accident complained of indeed by many, but 

 fcarcely attempted to be remedied or obviated by any, in a 

 rational way, till M. Geoffrey, whofe experiments fub- 

 jefted him greatly to the mifchief, employed his thoughts, 

 for his own fake, as well as that of the world in general, to 

 the effeftual prevention of it. 



The diffolution of the metals in the corrofive acid fpirits 

 are thofe, which lend out the moil copious and mod dan- 

 gerous vapours. The exhalation of quickiilver, of anti- 

 mony, and of lead and copper, arc all in themfelves greatly 

 hurtful, as well as the fiery vapours of fpirit of nitre, fea- 

 falt, or vitriol ; and if either of thefe is fingly fo, how 

 pernicious mufl they need be in thofe cafes, where two of 

 them are joined together in fuch a manner, as that this 

 union fends up infinitely more vapours than would other- 

 wife arife ; in this cafe the utmoft care is neceflary to pre- 

 vent the chemift from falling a facrifice to his zeal for his 

 difcoveries. 



The common way of avoiding this danger, is by making 

 the folution either abroad in the open air, or in a chimney ; 

 but fometimes thefe cautions cannot be ufed, and under 

 fome circumitances they are ineffeftual. This gave occa- 

 fion to M. Geoffroy to ufe a method, which he afterwards 

 propofed to the public, of flopping the nfe of the vapours 

 entirely, or at leafl of diminifhing them fo greatly, that 

 they fhall be harmlefs and unperceived. All that was necef- 

 fary to this, feemed to him to be the contriving to cover the 

 furfaceof the fluid with fome body, capable of retaining thofe 

 vapours, yet not capable of dillurbing the operation of the 

 menflruum on the metal ; and the common expreffed oils 

 of fruits, as the oil of olives, almonds, or the like, were 

 found capable of happily performing this efi'eft ; and that 

 particularly, as they would eafily receive into themfelves 

 the acid falts which arife in the conPiift. The thing which 

 gave this gentleman the hint of the difcovery was, that in 

 the boiling of fugars, honey, or the like fubftances, when 

 there is any danger of their boiling over the veffel, the 

 pouring in a little oil flops the fwelling. In the metallic 

 folutions it has the fame effecl ; and that heightened by 

 this good confequence, that by keeping in the fiery vapours 

 of the acid, it returns them back upon the metal, and by 

 this means does, in effeft, add greatly to the power of tjie 

 menflruum. 



This method of ufing oil has indeed three advantages. 

 I. The preferving the operator from the injuries of the 

 vapours. 2. The greatly moderating of that violent rare- 

 faftion, which is often of ill confequence. And 3. The fame 

 quantity of t^-e menflruum, by this means, diflfolves more of 

 the metal. The bell method of making folutions with this 

 advantage is this : firft, wet the furface of the metal to be 

 diflolved with water, or fpirit of wine ; then pour a little 

 water, or fpirit of wine, into the glafs in which the folution 

 is to be made, this will prevent the d\\ from flicking to the 

 furfnces of either ; then put the metal into the glafs, and 

 9 pour 



