238 



ASSAYING-ATHLONE. 



ASSAYING, (a.) This process has been very 

 much improved of late years, chiefly by the labours 

 of Gay Lussac in Paris, who turned his attention to 

 it when made master of the mint. The method 

 formerly employed has been explained in the arti- 

 cle in the body of the Encyclopedia, under the 

 same title. Its disadvantages, as applied to silver, 

 were the length of time taken in the operation, and 

 its not affording a sufficiently accurate result. The 

 cause of the inaccuracy is, that when silver fuses in 

 contact with air, it absorbs a considerable quantity 

 of oxygen, with which it parts again at a lower 

 temperature. This frequently causes a spirting, 

 and consequent loss of material. The workman 

 was long familiar with this phenomenon of the 

 spirting of the metallic button, but the true cause of 

 it was but comparatively recently discovered. The 

 oxygen is not supposed to be in a state of chemical 

 union with the silver in this state ; that is, no oxide 

 of silver is formed, but the oxygen is supposed to 

 be in a state analogous to that in which it exists 

 when in platinum sponge. (See Absorption, Sup- 

 plement.) Another cause of failure arose from 

 the aptitude of a little silver to sink into the pores 

 of the cupel. From these causes, the differences 

 in two trials made with the same silver often 

 amounted to p. c. notwithstanding all the care 

 and attention which could be bestowed on the 

 process. Where the operator was not very care- 

 ful, the error amounted even to , or -^j of a per- 

 centage. This uncertainty was particularly felt 

 where the alloy contained from 50 to 90 p. c. sil- 

 ver. In the cases of purer, and also of more adul- 

 terated alloys, the process by cupelation gave 

 pretty uniform results. But it is exactly silver of 

 the above content that is most frequently submitted 

 to analysis. 



The plan now had recourse to is at once sim- 

 ple and effective, and has proved of immense 

 service in the arts and manufactures. Formerly, 

 from the imperfect state of analysis, manufactured 

 silver articles which should contain by law a cer- 

 tain percentage of silver, were generally made 

 somewhat richer, in order to avoid all risk of col- 

 lision with the law. The loss sustained in this 

 way, in Paris alone, used to be enormous. Such 

 precautions are now unnecessary. The mode of 

 analysis followed is all but perfect, and the true 

 percentage in silver of the article analysed can be 

 determined with the utmost accuracy. Gay Lus- 

 sac's plan consists in dissolving a certain weight of 

 the alloy in pure nitric acid, and measuring exactly 

 the quantity of a solution of common salt of known 

 strength, that is, required to precipitate the whole 

 silver in the form of chloride of silver, which is 

 quite insoluble in water and dilute acids. The 

 content in silver is not estimated by the weight of 

 the precipitated chloride of silver, but according to 

 the measure of the solution of salt that is found 

 necessary. It is known that the silver is entirely 

 precipitated when, on the addition of another drop 

 of the solution, no milkiness is produced. In a 

 solution weighing 1000 grains, a quantity of silver, 

 amounting to the -j^j of a grain, causes a distinct 

 milkiness ; and if the solution be allowed again to 

 clear itself, the precipitation of the -^ grain may 

 still be observed. The milky solution should be 

 strongly shaken a minute or two, when in a few 

 seconds it becomes clear enough to admit of any 

 further precipitation being seen. If we suppose 

 the quantity of alloy operated on to be 10 grains, 

 the exact quantity of common salt necessary to 

 precipitate 10 grains of pure silver should be dis- 



solved in a vessel graduated lo 1000 parts. It 

 will be obvious, that whatever part of the 10 

 grains be silver, must be indicated by the measure 

 of the solution that is required before an additional 

 precipitate cease to be formed, when a drop of the 

 solution is added. The presence of lead, copper, 

 or other metals, does not alter in the least the 

 quantity of common salt required. In the manner 

 above described, a much greater degree of accuracy 

 is attained than is possible by the process of cupel- 

 ation, and where many trials are made much time 

 is spared. The chloride of silver which is precipi- 

 tated, is not thrown away, but is reduced, by 

 bringing it well washed in contact with pure muri 

 atic acid, and iron, or zinc ; chloride of zinc or iron 

 is formed and dissolves, while silver, in the metallic 

 state, remains. 



The process for assaying gold has been so 

 imperfectly described, that it may be well to add 

 here a short additional description of the pro- 

 cess really employed. The piece of gold is first 

 tried with the needles and test-stone. These 

 needles are composed of different alloys of gold 

 with silver and copper. The test-stone is a variety 

 of black-slate. A streak is first made with tlie 

 alloy, to be tested by rubbing it upon the test-stone, 

 and beside that, another streak with a needle, the 

 composition of which is known, and which is sup- 

 posed to be nearest that of the alloy under exam- 

 ination. If the streaks resemble each other in 

 colour, to determine which a considerable amount 

 of experience is required, the alloy is supposed 

 to have the same composition. When by these 

 means the composition of the alloy is approxima- 

 tively determined, it is hammered out into thin 

 sheets, and mixed with 3 times as much pure sil- 

 ver as there is of gold ; and to this mixture is 

 added three or four times its weight of lead, and the 

 whole tixed together in a cupel. The gold and 

 silver remain behind, the copper is oxidated and 

 sinks into the pores of the cupel, along with 

 the lead. The gold is then separated from the 

 silver by solution in nitric acid. For the success 

 of this operation, it is essential that the gold 

 amount to about \ of alloy of gold and silver, as 

 in this case the gold that is left retains the form 

 of the alloy, and can be readily taken out, washed 

 with pure water, and weighed. 



ASTORIA; the name given to a small fort, or 

 trading post, formed by Mr Astor, at the moutli of 

 the Columbia river, as a settlement for fur traders 

 belonging to the company which he undertook to 

 establish. One of the main objects in this com- 

 mercial enterprize was to establish a company of 

 traders belonging to the United States, as a rival to 

 the great North-West Company, the Mackinaw 

 Company, and other associations belonging to Great 

 Britain, and thus to cause the traffic in peltries, 

 and the wealth arising from it, to centre in New 

 York. On the breaking out of the war between 

 Great Britain and the United States, Fort Astoria 

 fell into the hands of the British, and the trade in 

 peltries was forthwith engrossed by the North- 

 West Company and other associations. See Wash- 

 ington Irving's interesting work, entitled "Astoria." 



ASTRABAD. See Persia, in Supplement. 



ATHLONE; a town of Ireland, situated on 

 both sides of the Shannon, fifty-nine miles west from 

 Dublin. It is conjectured that Athlone is only a 

 corruption of Ath-Luain, Moon Ford, or Ford of 

 the Moon. The portion of the town which lies on 

 the eastern bank of the Shannon was termed Eng- 

 lish Town, and is situated in the county of West- 



