A M A 



A M A 



hfrts to mercury when applied to its furface ; aiid, vk'.icn a 

 pintc of this, fiifper.dcd to the arm of a balance, is brought 

 in contaCl with mercury, a greater or lefs cour.terpoifc will 

 be required to break, the adhefion, as the chemical affinity 

 between the two is flronger or weaker. (See Adhesion.) 

 Nor is this adhcfion an effee'l taking place merely at the 

 pline of contact, but an actual penetration or abforption of 

 the mercury is produced by the ether metal : thus, when a 

 plate of gold is placed in contact with mercury, not only the 

 lurface of adhellon is whitened by the mercury, but, after 

 remaining in this ftatc a few hours, the gold will become 

 brittle, and particles of mercury- may be obftrved through 

 its whole fubftance, having no doubt been drawn up through 

 its minutell porcs by the force of chemical attraftion. 



During amalgamation, as is the cafe in all other inllances 

 of fir.iple folution, a confiderable quantity of caloric is ab- 

 forbed, producing the fenfation of cold, and lowering the 

 tliermonieter. This is rendered very fenfible to the touch, 

 by rubbing together in the palm of the hand equal parts of 

 an amalgam of bifmuth and an amalgam of lead ; the two 

 folids will almoft immediately become fluid, and a very con- 

 fiderable cold will be produced. The fa:ne may be (hewn 

 by the thei-momcler : if a quantity of mercury is heated to 

 about 80'' Fahr. and the bulb of a thermometer wrapped 

 round with tmtoil is then imrnerfed in it, a fpeedy folution 

 will take place, and at the fame time the mercury in the 

 thermometer will dcfcend a few degrees. 



Another remarkable phenomenon of amalgamation is the 

 difpofiticn to oxydate which both metals exhibit while the fo- 

 lution is going on, and even after it is completed : it is im- 

 poffibie to combine biimuth, tin, or lead, with mercury, 

 without obferving as the proccfs advances the formation of a 

 quantity of black powder, which rifes to the furface of the 

 metals, and is a compoui:d oxyd of mercury and the other 

 metal. Upon this alfo depends Dr. Prieftley's fimple and 

 ingenious method of feparati.ig from mercury a large pro- 

 portion of the lead, &c. with which it is ufually contami- 

 nated ; for this purpofe nothing more is neccfiary than agi- 

 tation of the mercury in a bottle, with a little water, till it 

 ceafes to be dilcolourcd, or, in other words, tiU the amal- 

 gam is almoil wholly decompofed. Hence too is explained 

 the obfervation of Ifaac HoUandus, that gold and fiber may 

 be calcined in a reverbcratory furnace, if they have been 

 previoufly mixed with mercuiy. 



§ 3. General Properties' of y^mafgams. 



The fpecific gravity of amalgams, as of all other alloys, 

 is different from the mean fpecific gravity of their com- 

 ponent parts : fometmies it is greater, at other times lei's ; 

 and, according to Gellert, the amalgam of filver is of fupe- 

 rior fpecific gravity even to mercury, the weightiell; of the 

 two ingredients. This takes place, however, only at a low 

 tempei-ature ; for it was found by Sage that the amalgam of 

 ■ filver, when heated, floats on the furface of mercury. 



The more decidedly crj'ftalline form of amalgams, owing 

 to their foft or femi-fluid itate, at a moderately warm tempe- 

 rature, is a circumllancc that remarkably diftinguiflies them 

 from the pure metals. Any metal, when melted and cooled 

 very ilowly, will exhibit in its fracture a cryftalline ftrufture, 

 and the cryilals of which it is compofed may, by particular 

 management, be exhibited in a ftate of feparation from each 

 ether ; but fimilar appearances may be produced with much 

 greater eafe in amalgams. All amalgams are brittle, and 

 any of them, being broken, will exhibit a granular or lami- 

 nated texture, which, by the microfcope, will be found to 

 be owing to a multitude of minute cryllals, applied by the>r 



furface.^ to each other, but not adhering with any tonfider- 

 able force. Induced by thefe appearances, M. Sage, after 

 many trials, fucceedcd in obtaining regular cryftals of inoi'k 

 of the amalgams by the following method. Having pre- 

 pared a very fluid amalgam, by adding four, five, or fi:t 

 times a greater quantity of mercury than of the other me- 

 tal, he put it into a retort, and proceeded to d'llillation in 

 a fand-bath, till a fourth, or even a third, of the mercury 

 had been driven off"; the refidue, being then allowed to cool 

 very gradually, was found regularly cryftaUized at the bot- 

 tom of the veffel. He thus obtained filver amalgam in the 

 form of articulated tetrahedrons and aluminiform octahe- 

 drons, refembling the native dendritic filver. In the fame 

 manner the amalgams of gold, bifmuth, tin, and zinc, af- 

 fumed the form of regular cryilals, but thofe of copper, 

 arfenic, and antimony, reiuled to cryflallizc. 



Amalgams may be decompofed by heat, but the laft por- 

 tions of mercury are not driven off" without a much greater 

 heat tlian is required for the volatilization, of pure mercury. 

 Hence a large projioition of the volatile metals, fuch as 

 zinc and arfenic, unites with the mercury, and is carried 

 over with it, and even the more fixed ones, as gold and fil- 

 ver, arc thus rendered in part volatile. 



As each metal has its peculiar affinity for mercury, it is 

 cbvious that an amalgam may be decompofed by the addi- 

 tion of a metal that has a flronger attraction to mercury 

 than that of which the amalgam is compofed : upon this 

 lub']ei£t, however, no accurate experiments have as yet been 

 made, which is the more to be regretted, as it would much 

 aflilt the inveiligation of the difficult but important fubjetl 

 of metallic alloys. One amalgam may even decompofe an- 

 other in a great meafure, as is the cafe with the amalgams 

 of lead and bifmuth : thefe being made feparately, with a 

 quantity of micrcury ce'^ual to the other ingredient, will be 

 folid and friable, but, upon mixture, will combine into a 

 fluid fcaicely to be diilinguifhed by its appearance from pure 

 mercury : by flanding fome days, however, in a temperature 

 not exceeding 40° Fahr. cubic cryllals will be oepofited of 

 almott pure bifmuth. For otlier particulars lee the feveral 

 amalgams under the word Mercury. Encycloped. me- 

 thod, art. Amalgame. 



AMALGAMATION, in Metallurgy. See Silver 

 ores, extraSlon of. 



AMALI, in Ancient Gcographv, a people comprehended 

 under the appellation of Getas. 



AMALIA, in Entomology, a fpecies of papilio in the 

 Ihyinphales feftion, with indented wir.gs : upper fide brown, 

 underfide yellow with two ftreaks and fpots of blue, the lower 

 ones marked with black dots. Fabr. Ent. Syft. tom. iii. 

 p. I. p. 129. fp. 398. Obf. In addition to this fpecific 

 character Fabricius fays, above the brown colour of the 

 wings inclines to fulvous, and the pofl.erior pair is marked 

 with an obfolete row of fulvous fpots. Beneath, the apex 

 of the anterior wings has a black mark, and two blue fpots 

 with a black character in the middle of each ; the exterior 

 margin, two ftreaks, and feven fpots on the pofterior wings 

 are blue, the latter with black dots in the middle. Inha- 

 bits SieiTa Leon. 



AMALLOBRIGA, in Ancient Geography, a town of 

 Spain, upon the Dwrius, to the fouth-eaft of Pallentia. 



AMALRIC, AuGERi, in Biography, an ecclefiaftical 

 hiftorian of the 14th century, dedicated to pope Urban V. 

 a hiftory of the popes, under the title of " Chronicon Pon- 

 tificale," brought down to pope John XXII. and faid to be 

 collected from more than 200 writers. 



AMALTHiEA, in Alytholo^x, the Cumxan Sibvl, who 

 6 ^' ii 



