1814.] Northumberland, Durham, &c. 345 



The remaining mines are parcelled out among various companies of 

 miners. The valuable estates of Lord Derwentwater belong to 

 Greenwich Hospital. They do not work any of their mines, but 

 receive one fifth of the ore raised in them as rent. This amounts 

 to between 3000 and 4000 bings of ore in a \ear. 



The quantity of silver extracted annually by Col. Beaumont from 

 his lead amounts to 15,000 ounces ; so mat the quantity of silver 

 annually raised in this county may be reckoned at about 3,750 lbs. 

 troy. 



6. Great improvements have been of late years made in the method 

 of smelting the ore. The consequence has been, that the produce 

 of lead has been considerably increased. The galena reduced to 

 small pieces is in the first place roasted in a flat oven-shaped furnace 

 by means of a reverberatory fire. It is kept moderately red-hot, 

 and is very frequently stirred up. Care is taken to prevent the heat 

 from rising so high as to melt the galena, and the process is stopped 

 when the ore begins to soften. This process renders the galena 

 darker coloured. A white smoke is exhaling during the whole 

 process, but I could not perceive in it the smell of sulphurous acid. 

 The smoke, I believe, is chiefly oxide of antimony, which carries 

 with it a portion of oxide of lead, and no doubt the sulphur with' 

 which these metals were combined is acidified, though I did not 

 perceive any distinct indications of this by the smell. This matter is 

 collected in long horizontal chininies constructed on purpose, and 

 is known in the smelting-houscs by the name of lead fume. It is 

 sold as a paint. I had the curiosity to examine a quantity of it. Its 

 specific gravity was .VS8:2, and I found it a mixture of about five 

 parts carbonate of lead and three parts oxide of antimony, not 

 reckoning a little water and earthy matter, which was probably only 

 accidentally present. We see from this that a portion of the lead 

 flies off during the roasting. Perhaps this loss might be somewhat 

 diminished by keeping the fire as low as possible consistently with 

 the object in view. It is probably the antimony that facilitates the 

 escape of the lead in this process. This circumstance suggests a 

 reason why the specular galena yields more lead tban the variety 

 with a waved surface. The first contains no antimony, and probably 

 sustains in consequence less loss of lead during the roasting. The 

 roasted galena I find unaltered in its properties. It is still as before 

 the process composed of L'5974 lead and 4 sulphur. Hence the 

 only use of the roasting is to drive off the antimony. 



The roasted ore is then thrown along with pit-coal upon an open 

 hearth, and the fire is kept up by means of a pair of bellows driven 

 by water. Some peat is always put before the DOZZle of the belli WS 

 to divide the blast. A little lime is nbo occasionally thrown in, the 

 object of which is to prevent the slag from running away in a liquid 

 state. In this hearth the had is reduced to the metallic state, and 

 drops down into a cavity in the bottom of the hearth. When this 

 eavity is once full,, the lead runs along a channel cut for it into ati 



