ASSAYING. 



tire quantity of this metal about thrice 

 the weight of pure gold. 



The proportion of lead to the alloy of 

 copper, or other base metal, is nearly the 

 same as for silver ; which will be shewn 

 particularly in the annexed table. The 

 heat necessary in the process is greater 

 than for silver, and may be used with 

 freedom, as none of the gold is lost by vo- 

 latilization. The lighting of the fused 

 globule of gold takes place as in silver. 

 The button is cooled, taken out and 

 weighed, then hammered flat and anneal- 

 ed, and afterwards laminated between 

 steel rollers to a thin plate about the sub- 

 stance of a wafer, again heated to red- 

 nesSj and then coiled up into a spiral roll. 

 The button of gold, when it lightens, still 

 retains a minute portion of lead ; this may 

 be got rid of by its being kept a little time 

 in fusion in a clean vessel. The lead en- 

 tirely disappears after parting. 



The spiral roll is called a cornet, and 

 when prepared is put into a glass matrass, 

 shaped like a pear, in order to part the 

 silver from it, and about thrice its weight 

 of pure nitric acid poured on it moderate- 

 ly diluted, (so as to be about 1.25 specific 

 gravity.) The glass is set on a sand bath, 

 or over charcoal, to boil. When warm, 

 the acid dissolves the silver ; as long as it 

 continues to act, the cornet is studded 

 with minute bubbles : when these dis- 

 continue, or are united in one large one, 

 it is a sign that the acid has ceased to ope- 

 rate. About twenty minutes are requir- 

 ed for this process. 



The cornet is now corroded through- 

 out, having lost its silver ; it retains the 

 same form, but is very slender and brittle. 

 It is of importance to the accucray of the 

 assay that it should not be broken. The 

 hot acid solution of silver is then poured 

 off with great care, and fresh acid, rather 

 stronger, is added, to clear away all re- 

 mains of the silver, and boiled as before, 

 but only for five or six minutes. It is 

 then decanted, and added to the first so- 

 lution, and the parting glass is filled with 

 hot distilled water, to wash off all remains 

 of the solution. A small crucible is to be 

 inverted over the glass while it is full of 

 water, the latter is then nimbly turned, 

 and the cornet falls gently into the cruci- 

 ble through the water ; which being 

 poured off, the crucible is dried and heat- 

 ed to redness under a muffle, when the 

 cornet shrinks extremely in every direc- 

 tion, becomes firm, and when cooled, re- 

 gains its metallic lustre, and is soft and 

 flexible. It is thea most accurately 

 weighed, and the process is finished. 



The final weight of the gold cornet in- 

 dicates the absolute quantity of this metal 

 in the assayed sample. The difference 

 between the weight of the button after 

 cupellation (deducting the silver added) 

 and the first sample, is the weight of the 

 copper, or other base metal in the gold ; 

 and the difference between the gold cor- 

 net, together with the silver added, and 

 the button after cupellation, is the quan- 

 tity of silver with which the gold was al- 

 loyed. 



The silver is usually recovered from 

 the solution left after parting, by immer- 

 sing in it plates of bright copper, which 

 dissolve and precipitate the silver in its 

 metallic form. 



Touch-needles for gold are formed in 

 the same manner as for silver, but more 

 of them are required, as the various com- 

 binations of three metals are to be exami- 

 ned by them in this case. Four sets of 

 them are usually employed ; one in which 

 pure silver is used for the alloy, another 

 in which the alloy is two parts silver and 

 one of copper, a third with two parts cop- 

 per and one of silver, and a fourth of 

 copper only. In trials with these nee- 

 dles nitric acid is of singular service ; a 

 drop of it is let fall on the streak of metal 

 on the touch-stone ; in eight or ten se- 

 conds it is washed off and the effect ob- 

 served. If the streak preservesits gold- 

 en brilliance unaltered, the metal is 

 judged to be of a certain degree of fine- 

 ness. If it looks red, dull, and coppery, 

 it is less fine ; but if the streak is almost 

 entirely effaced, it contains very little 

 gold. 



A peculiar set of weights are used for 

 assaying. 



The quantity of metal taken for an as- 

 say is always very small ; in this country 

 generally from 18 to 36 grains troy for 

 silver, and from 6 to 12 grains for gold. 

 This is the integer, and whatever be its 

 real weight, it is denominated the assay 

 pound. This imaginary pound is then 

 subdivided into aliquot parts, but differ- 

 ing according to the metal. The silver 

 assay pound is subdivided into 12 imagi- 

 nary ounces, each ounce into 20 penny- 

 weights; and for assaying, these again 

 into halves. 



The following is the table of the pro- 

 portions of lead required to different al- 

 loys of copper. In the three first columns 

 is shown the absolute increase of the 

 quantity of lead in alloys of decreasing 

 fineness. In the three last columns will 

 be seen the gradual diminution of the 

 protecting power of fine metal against 



