ALL 



ALL 



llii; fluid to tlie folij tlate. Let A B tlienbe a binan' mix- 

 ture of three parts A, and one B ; A is the leall fiilible of 

 the two and contratis Icafl in coohng ; it will iieccfrarily 

 liappcii therefore, upon the fuppofition that no ciiemical 

 silinity fubfilh between them, that when they are well 

 mixed by fiifion and then allowed to cool, A will harden 

 firll, and by it:* excefs in quantity will entirely envelope all the 

 iiK-lted particles of B with a crull impenetrable to the air, 

 : il capable of fupporting the whole atniofpheric prefTnre ; 

 . iierwards B will become folid and contra^, kaving 

 [art of the cell which it occupied while fluid, a perfedi 

 vacuum, at the fame time that thefc pores may cafily be 

 iiivllible even to common magnifiers; hence the rcfult 

 will be a mixture of Icfs than the mean fpccilic 

 [(ravlty. 



The change that takes place in the duclility of metals 

 wlien mixed together is generally brought forwards as one 

 of the moil llriking proofs of chemical combination ; even 

 here, however, difficulties occur that have not yet been ex- 

 jilained. Macquer lays it down as a conftunt fa6t that alloys 

 are lefs duftile tlian tlie metals of which they are compofed, 

 and Gellcrt in his C/jimie Mctallur^iquc infers, that the mix- 

 tare of gold with iilver is not a true alloy on account of its 

 ]unfecl duftility ; from the want of accurate experiments 

 it is perhaps impoffible at prefent to determine the queftion ; 

 but, fo far from the pofition of Macquer and Gellert being 

 iniiverfally true, the general rcfult of the fiifts which have 

 liL'cn hitherto afcertained, if rightly underftood, feems to 

 render the direft reverfe highly probable ; and that the 

 brittlenefs of alloys from duftile materials is in all cafes a 

 proof of fuperfaturation, or of mere mechanical mixture. 

 When to any quantity cf pure copper one third of zinc is 

 added, the alloy called brafs is produced ; and that this is a 

 chemical combination between the two metals may be in- 

 ferred from the remarkable change of colour and fufibility 

 of the mafs ; the duftility however of brafs is fully equal 

 to that of copper. But if the proportion of zinc is in- 

 creafed to an equality with the copper, the colour of the 

 alloy, inftead of being yellow like gold, will be nearly a 

 medium between that of brafs and of zinc, and its duftility 

 will be deftroyed ; thus fhewing, that the point of mutual 

 faturation of thefe metals is between one third and a half of 

 zinc to two thirds and a half of copper, and alfo that 

 brafs has little or no affinity with zinc. The duftility of 

 any metal depends on the ftrong cohefive attraftion of its 

 particles, which flide upon each other when inipreffed by any 

 external force inlUad of feparating ; now it may readily be 

 conceived that two duftile metals being intimately mixed fo 

 as that every particle of the one is in contaft with a particle 

 of the other, provided no very powerful affinity fubfiils 

 between them, may be broken by a blow which would only 

 liave nightly altered the relative pofition of homogeneous 

 cohering particles ; and therefore, that a brittle mixture of 

 two ductile metals does not neceflarily infer a chemical com- 

 bination between them. 



Change of colour, in the few cafes in which it occurs, 

 provided it is not intermediate between thofe of the elements 

 of any alloy, may be confidered as a very probable evidence 

 of chemical union ; of this kind is the golden colour of 

 brafs, and the filveiy white of arfenicated copper. But the 

 general fimilarityof colour between all the white metals and 

 their alloys, confines the apphcation of this external charafler 

 lo a very few inflances. 



One of the moft ftriking proofs of aftual combination 

 between the parts of an alloy, or at leaft. what is the molt 



difficult of explanation upon the thcon' of mere mechanical 

 mixture, is a remarkable increafe of fufibility ; this, in almoft 

 all cafes, is much greater than could be inferred from the 

 mean fufibility of its component parts ; thus equal parts of 

 tin and iron will melt at the fame temperature as is required 

 for equal parts of tiii and copper, or bronze, nutwith- 

 ftanding the great difference between the fufing heat 

 of copper and iron, when they are each of them pure. 

 So alfo an alloy of tin, bifmuth and lead, will melt in 

 boiling water, which is a lefs heat than is ncceffaiy for 

 the liquefaction even of bifmuth, the moft fufible of the 

 three. 



The oxydability of an alloy is generally either greater or 

 lefs than that of the fimple metals. Tin and lead for inllance 

 being mixed together and expofcd to alow red heat take fire 

 and oxydate almoft inllantaneoufly. 



Elective affinity takes place in the combinations of ractals, 

 as in thole of all other fubllances ; thus an alloy of copper 

 and filver is dcconipofable by lead. Again certain metals 

 refill luperfaturation, while others maybe mixed in almoft all 

 proportions, as cobalt may be combined with a certain pro- 

 portion of lead, but cannot even be mixed with a larger 

 quantity. Thefe enquiries, however, though highly interelt- 

 ing and intimately connefted with many of the ufeful arts, 

 have been almoft wholly negledled during the laft fifty years ; 

 and the experiments of Gellert, Kraaft and Lewis, ilill con- 

 tiiuie to be our only authorities. JVIany peculiar difficulties 

 attend the inveftigation of the general principles, according 

 to which metals att on each other, and the general ])henomena 

 ncceffarily attending fuch aftion ; it is a fubject that may 

 demand the abilities, and will recompence the attention, of the 

 grcatefl and moil accurate philofopher, and which unfor- 

 tunately has hitherto received lefs notice than any other 

 branch of chemical enquiry. 



Alloy of coinage. See Assay. 



ALL-SAINTS, \n Geography. See ALV-Saints. 



ALL-SEED, in Botany. See Linum and Cheno- 



PODIUM. 



ALL-SPICE. See Myrtus. 



ALLSTADT, or Allstett, in Geography, a very 

 ancient town of Germany, in the circle of Upper Saxony, 

 and principality of Eifenach ; 26 miles north of Weimar, 

 and five fouth-fouth-eail of Sangerhaufen. The emperor 

 Otho had a palace in this town, and held a diet here in 974, 

 It belongs to a bailiwick of the fame name, lying bctweea 

 that of Sangerhaufen in tlie eleftorate of Saxony, the prin- 

 cipality of Qiierfurt, and the bailiwick of Bocklledt, in the 

 county of Mansfcld. 



ALLUDSJE, a town of Arabia, 14 miles eaft-north- 

 eaft of Beitel Fakili. 



ALLUM. See Alum. 



Allv mbaddy, in Geography, a town of Hindoftan, in the 

 country of the Myfore, 63 miles call of Seringapatam, and 

 50 fouth of Bangalore. 



Allum Bay, lies round the Needles point, or north 

 eaft from the rocks fo called, at the weft end of the Ifle of 

 Wight, on the coaft of Hampfhire. It has good anchorage, 

 and a fufficient depth of water, not far from the bottom of 

 the bay, and out of the ftrong run of the tide, which is fre- 

 quently very rapid, and accelerates or retards the motion of 

 a vefiel, as a fhip falls with or againft its diredtion, to an 

 aftonifliing degree. 



ALLUME'E, Fr., in HeraHry, a term applied to the 

 eyes of a bear, or other beall, when th-y are drawn fparkling 

 and red. 



7 ALLUMETiE, 



