74 LEAD 



On comparing the expense of each operation, as given, in the foregoing abstract, 

 with the amounts stated as the cost of each separate process, they will be found to 

 be widely different ; but it must be remembered that the whole of the substances 

 elaborated are far from being subjected to the various treatments described. 



In order, therefore, to give an idea of the relative proportions which are passed 

 through the several departments, it may be stated that in an establishment in which 

 the ores are treated in the Castilian furnace the following were the results ob- 

 tained : 



One hundred parts of raw ore yielded : 



Boasted ore . . 85 



Hard lead 42 



Soft 36 



Rich 9 



Dross and litharge re- treated . . . . . . 18 J 



It may be remarked that for the treatment of ores of good produce the reverbera- 

 tory furnace and Scotch hearth are to be preferred, but for working minerals of a 

 low percentage the blast-furnace may generally be substituted with advantage. 

 The slag-hearth, from the amount of fuel consumed and loss experienced, is a somewhat 

 expensive apparatus, and might in many cases be advantageously exchanged for the 

 Castilian furnace. 



It is well known that the losses which take place in this branch of metallurgy are, 

 from the volatility of the metal operated on, unusually large. In those establish- 

 ments, however, in which due attention is paid to fluxes and a proper admixture of 

 ores, as well as the condensation of the fumes, a great economy is effected. 



In some instances flues of above five miles in length have been constructed, and the 

 most satisfactory results obtained. The attention of lead-smelters is being daily more 

 directed to the prevention of the loss of metal by volatilisation, and those who have 

 adopted the use of long flues have been, in all cases, quickly repaid for their outlay. 



As an example of tie great extent to which sublimation may take place on the 

 scale employed in large smelting works, we may mention the lead-works belonging 

 to Mr. Beaumont in Northumberland. Formerly the fumes or smoke arising from 

 various smelting operations escaped from ordinary chimneys or short galleries, and 

 large quantities of lead were thus carried off in the state of vapour, and deposited 

 on the surrounding land, where vegetation was destroyed, and the health of both 

 men and animals seriously affected. This led to various extensions of the hori- 

 zontal or slightly-inclined galleries now in use, and the quantity of lead extracted 

 rapidly repaid the cost of construction. The latest addition of this kind was made 

 at Allen Mill, by Mr. Sopwith, the manager, and completed a length of 8,789 yards 

 (nearly five miles) of stone gallery from that mill alone. This gallery is 8 feet 

 high and 6 wide, and is in two divisions, widely separated. There are also upwards 

 of 4 miles of gallery for the same purpose connected with other mills belonging to Mr. 

 Ueaumont in the same district, and in Durham. The value of the lead thus saved from 

 being totally dissipated and dispersed, and obtained from what in common parlance 

 might be called chimney-sweepings, considerably exceeds lO.OOOZ. sterling annually, 

 and forms a striking illustration of the importance of economising our waste pro- 

 ducts. 



In lieu of long and extensive flues, condensers of various descriptions have from 

 time to time been introduced, but in most instances the former have been found to be 

 more efficient. 



When, however, water can be procured for the purpose of cooling the condensers, 

 excellent results are generally obtained. J. A. P. 



See LITHARGE ; RED LEAD ; SOLDEB ; SUGAR or Acetate OF LEAD < Tfra METAI ; 

 and WHITE LEAD. 



LEAD AssAtmo The ores submitted to assay are galena or sulphide of lead, 

 cerussite or carbonate of lead, anglesite or sulphate of lead, and pyromorphite or 

 phosphate of lead. For assay purposes, the ores of lead may be divided into two 

 classes 1 



The first class comprehends all the ores of lead which contain neither sulphur nor 

 arsenic, or in which they are present in small proportion only. 



The second class comprises galena, together with all lead ores containing sulphur 

 or arsenic. 



A common wind or air furnace is best adapted for making lead assay?. For this 

 purpose the cavity for the reception of fuel should be 9 inches square, and the height 

 of the flue-way from the fire-bars about 14 inches. For ordinary ores a furnace 8 

 inches square and 12 inches deep will be found sufficient ; but as it is easy to rcgu- 



