206 ANNUAL OF SCIENTIFIC DISCOVERT. 



PRECIPITATION OF METALS BY MEANS OF MAGNESIUM. 



!M. Roupsin has piibli^hod a ])apor on the action of ma'jnesiura 

 on mct;illit' sohitioiis, and on its a|)i)licalion to toxii-olot^^ical nv 

 scari'hcs, whit-ii shows tliat niaqncsiiun ispartirnhirly well adapted 

 for the precipitation of otlier metals fnjui sohitions of their salts. 

 It is a general prineiple, tiiat one metal will jn-ecipitate from a 

 saline solution any other wiiich is less readily oxidal)le tlian itself; 

 but some metals, by no means amon<^ the most oxidalile known, 

 had, nevertheless, when M. Roussin began his reseai'ches on this 

 subjeet, resisted all attemjits to precipitate them by the contact of 

 anothi'r metal witii their saline sohitions. With two exeejjtions, 

 however, all the metals alhuled to an; precipitated in the metallic 

 state by maiinesiiim, the two exceptions being chromium and 

 manganese, whii-h appear to be prei-ipitated as oxides. Among 

 the metals which M. Roussin has precipitated in the metallic state, 

 by means of magnesium, from slightly acididated solutions of 

 their salts, are gold, silver, platinum, bismuth, tin, mercury, cop- 

 per, lead, cadmium, thallium, iron, zinc, cobalt, and nickel. The 

 j)recipilati'd metals, when washed from the saline liijuid, and then 

 dried and compressed, possess a very remarkaljle degree of l)ril- 

 liancy. Iron, cobalt, and nickel, so precipitated, are highly mag- 

 netic; zinc takes the form of a large spongy mass, which the 

 least compression renders brilliant. Magn<,'siuni does not jirecipi- 

 tate aluminium at all, and chromium and manganese, as already 

 mentioned, it precipitates as oxides. It does not precipitate 

 arsenic or antimony, though it decomposes their salts, the arsenic 

 or antimonv living oil" in combination with hvdrogen. M. Rous- 

 sin shows that great advantages result from the substitution of 

 magnesium for the metals ordinarily employed in toxicological 

 researches for the detection of these and other metallic poisons ; 

 but into that part of his subject it would be beyond our province 

 to follow him. Ills onl}' further statement respecting magnesium, 

 calling for mention here, is one relating to its use as a voltaic 

 element. " The foregoing qualities," he says, " encouraged the 

 hoj)e that a substitution of magnesium for zinc in ordinary jiiles 

 would oQer a great electro-motive force ; and experiment con- 

 firmed this theoretical inference. A small plate of magnesium, 

 0.1 grain in weight, placed beside a plate of copper in a small 

 tube of glass of six centimetres cube, filled with acidulated cop- 

 per, produced in less than ten minutes an electro-magnetic ap- 

 pearance, and illuminated a Geisler's tube ten. centimetres long. 

 If magnesium should ever become cheap, this would decidedly 

 be the best way of producing electiicity." 



In a note to his paper, M. Roussin states that he has obsei'ved 

 that a sodium amalgam, shaken up with an acidulous solution of 

 a salt of chromium or of a salt of manganese, changes to an 

 amalgam of chromium or of manganese, as the case may be ; 

 and that an amalgam of either of these metals, obtained in the 

 manner indicated, when distilled in a current of hydrogen, after 

 haAing been first carefully washed in acidulated water, leaves the 

 pure metal in the form of a pulverulent sponge. " The amalgam 



