SILVER. 



Mr. Prouft found this tarnifhing matter to be a fulphuret 

 of filver. The thinneft coat of gum, or of varnifh, com- 

 pletely defends the furface of filver from tarnifhing. 



Silver combines vnth phofphorus, forming a phofphurct 

 of filver. This combination is effefted by heating in a 

 crucible equal parts of filver and phofphoric glals, with 

 one-fourth their weight of charcoal powder, or, what is 

 better, faw-duft. This compound is of a white colour. It 

 is brittle, but may be cut with a knife. It is, like the ful- 

 phuiet, decompofable by heat. 



Silver combines with f;veral metals, forming alloys. 

 The alloy of filver with gold, wlien the former is in a very 

 fmall quantity, is of a much paler colour than gold. Thefe, 

 like all other compounds, are doubtlcfs definite, and hence 

 we ftio«ld expeft, that when thefe metals combine in the 

 ratio of the weights of their atoms, which will be loo filver 

 to 140 of gold, the alloy would be the mod perfeft. And 

 the next perfedl would be two atoms of one to one of the 

 other. It is ftated by Mufchenbroeck, that the hardeil 

 alloy of thefe two metals is with two parts of gold to one of 

 filver. 



Silver, as well as rendering gold much paler, gives it a 

 greenifh tinge. This alloy is more fufible than gold, and 

 hence is employed as a folder for that metal. 



Silver does not form any linking alloy with platinum. 

 Indeed it rather appears to be a mixture than a combination. 

 As is the cafe with lead and zinc, the two metal? feparate, 

 when kept fome time in a ttate of fufion. This faft is cor- 

 roborated by the circumftance, that filver can fcarcely be 

 made to unite two pieces of platinum together, when ufed 

 as a folder, while gold can be employed for tliat purpofe 

 with the greateft fuccefs. For the other alloys of filver, 

 fee the relpeftive metals. 



Salts of Silver. — Thefe confift of the oxyd of filver com- 

 bined with an acid, fome of which only are foluble in water. 

 The prefence of the foluble falts of filver is eafily de- 

 tefted by muriatic acid, or any foluble faline compound 

 with that acid, by occafioning a denfe white precipitate, 

 which foon changes to a purple colour when expofed to 

 the fun's light. 



The infoluble falts of filver have the property of coating 

 bright copper with filver, when rubbed upon it with a little 

 moifture. Salts of mercury would give the fame white ap- 

 pearance, but this would be diftinguifhed from filver by 

 being capable of diflipation by heat. Salts of filver be- 

 come black with the hydro-fulphurets of the alkalies. And 

 gallic acid gives a brown precipitate. 



Sulphate of Silver. — Sulphuric acid has no aftion upon 

 filver at the common temperature. When, however, this 

 metal is boiled with the acid, the filver becomes oxydated, 

 fiUphurous acid gas is difengaged, and fulphate of filver is 

 formed, which is a white mafs, fparingly foluble in water, 

 except an excefs of fulphuric acid be prefent. The latter, 

 on evaporation, affords cryllals of a brilliant filvery while- 

 nefs, in the form of needles or tine prifms. 



This fait is foluble in nitric acid. 



When heated, it firft fufes, and if the heat be raifed, it 

 is decompofed, fulphuric acid and oxygen efcaping, leav- 

 ing the filver in its metallic form. 



This fait is decompofed by the alkalies and earths, and all 

 thofe foluble falts, the acids of which form infoluble com- 

 pounds with filver. Bergman has ilated, that 100 parts of 

 metallic filver, precipitated from nitric acid by fulphuric acid, 

 give 134 of the fulphate. Allowing the 100 of filver to 

 have taken 7 of oxygen, there will remain 28 for the ful- 

 phuric acid. This, in 100, will give fulphuric acid 22, 



and 78 of oxyd of filver. If this fait be compofed of 

 one atom each of acid and bafe, then, by Dr. Wol- 

 lalton's fcale, the proportions would be 25.5 acid, and 

 74.5 oxyd of filver. Dalton's numbers would give very 

 nearly the fame refult. 



Sulphate of Silver. — This fait, like the latt, is fparingly 

 foluble in water. In other refpcds, it is but httle known. 



Nitrate of Silver. — The nitric acid afts with confiderable 

 violence on filver, affording red lufFocating fumes, occafioned 

 by the copious difengagemcnt of nitric oxyd. If the acid 

 and the filver be pure, the folution becomes clear and co- 

 lourlefs, without refiduum : if the acid contains muriatic 

 acid, which is often the cafe with the acid of the (hops, 

 then a denfe white powder will fall down, which becomes 

 purple in the fun-(hine, and is the muriate of filver : if the 

 filver contains gold, a purple powder will be left at the hot- 

 torn of the velfel : if it contains copper, the folution will be 

 of a green colour, of greater or lefs intenfity, depending 

 upon the quantity of that metal. 



The folution of filver affords cryftals on evaporation : 

 they are of a prifmatic form, but differ in their number of 

 fides ; they do not change by expofure to the air, but are 

 very foluble in water. Thefe cryftals, when heated, firll 

 melt ; the heat being raifed, the water of cryftallization 

 efcapes, but the mafs ftill remains liquid : in this ftate it is 

 frequently caft into moulds, in which it aflumes a folid form 

 on cooling. Thefe (ticks, which are employed in furgery 

 under the name of lunar catiflic, are of a grey colour, and 

 when broken exhibit a cryflalline appearance. 



A more violent heat than that required for its fufion 

 decompofes it, nitrous gas and oxygen being difengaged. 



This decompofition is much more rapid when it is heated 

 in contaA with inflammable matter. If thrown upon burn- 

 ing coah, it detonates. 



If filk, cotton, leather, ivory, and many other bodies, be 

 moiftened with nitrate of filver, and the part be afterwards 

 moiftened, when a ftream of hydrogen gas is applied to it the 

 filver becomes reduced, and appears with its metallic lullrc. 

 A (lick of phofphorus dipped in nitrate of filver foon becomes 

 coated with metallic filver. 



This fait has the property of detonating with fulphur or 

 phofphorus, by being (truck fmartly with a hammer. 



Nitrate of filver is decompofed by all the earths which 

 form falts, and by the alkalies, by combining with the acid. 

 Ammonia, however, does not only precipitate the oxyd, but 

 afterwards combines with it, forming a compound having 

 alarming fulminating properties. The following is the pro- 

 cefs recommended for its preparation. 



From the nitrate of filver precipitate the oxyd by means 

 of lime-water : feparate the oxyd, and dry it upon blotting- 

 paper : upon this oxyd pour pure cauitic ammonia : let this 

 remain for twelve hours. If a pellicle be formed upon the fur- 

 face, add a httle more ammonia, which will take it up. A 

 black precipitate will be found at the bottom of the veffel, 

 which is the ammoniate of filver, and is the fulminating 

 fubftance to be obtained. This precipitate is to be carefully 

 coUefted, and laid in very fmall quantities upon feparate bits 

 of blotting-paper, to dry. When dry, the flighted touch 

 or rubbing motion caufes a violent explofion. Thofe unac- 

 cuftomed to it (hould begin with the fmalleft pofllble quan- 

 tities, as ferious accidents have happened by exploding it 

 in too large quantities. The liquid part from which the 

 fubftance was feparated will be found to be a folution of the 

 fame : if it be heated in a glafs retort, a portion of it is de- 

 compofed, and the gafeous produfts difengaged : in a little 

 time, fmall brilliant cryftals of the fame fubftance appear ; 



thefe 



