SOAP.
764
free from suoli metals as would interfere with itstreatment on the cupel, it may be at once sub-mitted to cupellation; but otherwise, it must bescorified on charcoal until these substances areremoved by volatilization or by slagging off. Theconcentration of the silver, as well as the finalcupellation, take place on specially formed cupels0-7 inch in diameter and 0-4 inch high, made ofmoderately fine bone-ash, which is, for the cupella-tion process, covered with a layer of bone-ash ofvery fine quality. The silver-lead alloy is submittedto the action of an oxidising flame, and quicklyassumes a bright metallic appearance, commencingat the same time a rapid rotatory movement. Thisoperation should be conducted at as low a tempera-ture as is compatible with such a movement, other-wise the litharge is liable to sink into the cupel.The concentration must not be carried too far, as thesilver would then be liable to spit. The cupel is nowwithdrawn very gradually from the flame and allowed
to cool, when the metallic globule is removed fromthe litharge surrounding it.
In cupelling this button, it is placed in the centre ofthe cupel, and an oxidising blowpipe flame is made toplay on the bone-ash surface immediately surround-ing it without touching it, so as to insure theabsorption of the litharge by the cupel, and to pre-vent scales of litharge being formed beneath theglobule itself.
Considerable practice is required in order toproperly conduct the process. It is, however, wellworthy of more attention than it has hitherto re-ceived, and is capable, in able hands, of giving veryexcellent results.
Statistics. —The more important statistics relat-ing to silver have been already given in the articleon Gold ; but it may be interesting to add theaccompanying table, which shows the produce ofdifferent parts of the world in 1800, 1850, and1865:—
TABLE SU0WIX3 THE APPROXIMATE YIELD OF T3IE PRINCIPAL SILVEE-PEODDCINO COUNTRIES OF THE WORLD
(1'IIILLIPS).
Country.
Great .Britain,...
Hartz.
Prussia,.
Saxony,.i.
Australia, New Zealand, British Columbia ,
Chili,.
New Granada,.
Total,.
1800.
1850.
1865.
Pounds
Percentage
Pounds
Percentage
Pounds
Percentage
Troy.
of Total.
Troy.
of Total.
Troy.
of Total.
58,150
2-5
60,000
2-1
58,000
1-5
20,400
48,500
0-7
15,000
0-4
1*7
60,500
1*5
31,500
M
28,000
0-6
21,200
0-7
68,000
1-7
141,000
GO
63,600
2,500
2-2
0-1
80,000
2,500
2-0
87,000
5,000
3-1
92,000
2-2
0-2
18,000
0-4
—
--
25,000
0-6
125,000
4-4
110,000
2-8
—
—
10,000
0-4
9,500
0-2
18,300
0-8
238.500
8-4
299,000
7-3
271,300
11*6
130,000
4-6
136,000
3-3
401,850
17-2
303,150
10-7
299,000
7*4
5,000
0-2
13,000
0-5
15,000
0-4
1,200
—
675
—
1,500
_
1,440,500
61-7
1,650,000
58-4
1,700,000
42-3
17,400
0-7
1,000,000
25-0
2,337,300
100-0
2,827,425
100-0
4,017,000
100-0
SOAP. —■ Savon, French ; Seifc, German ; Sapo,Latin. —The term soap was formerly applied to allcompounds consisting of an alkali, an alkaline earth,or a metallic oxide, united to a fatty or oily acid, orother substance of an unctuous or oleaginous nature.This extended meaning of the term is, however, notnow recognized ; it is now applied to those combin-ations of grease or oil with the alkalies which, bytheir peculiar properties and solubility in water, aidthe removal of grease and dirt in the processes ofwashing and scouring. This cleansing influence isdue to what is termed a detergency; that is, a powerof rendering soluble in water the adhering dirt ofthe clothes and the skin, to which purpose soap isalmost exclusively applied. The alkalies themselves—potash and soda—possess this property of deter-siveness ; and the former, potash, under the form ofwood ashes, was used in the most ancient times by
the Hebrews, Egyptians, and Greeks, as an aid tocleansing processes. Free alkali itself, however,possesses a solutive property over fibrous materials,over even human skin, and hence the necessity ofcombining it in such a manner as to modify thisinjuriously corrosive action.
The remedy is the substitution of soap, which, byits slight excess of alkali, rendering soluble in andmiscible with water all the dirty grease of the clothesand oily exudations from the pores of the skin, is atthe same time detersive itself; for though composedof oil and alkali in a state of combination, it stillpossesses the influence of the latter without any ofits hurtfulness. Oleate of oxide of lead, formerlycalled lead soap, is insoluble, and constitutes thediachylon plaster of pharmacy. The analogous saltsof zinc and lime, formerly termed zinc soap and limesoap, are also insoluble.