FOR the next edition of my work, "The Plumber, and Sanitary Houses," my son, Mr. Bertram Hellyer, has searched through the records of the Patent Office and worked up a brief history of the apparatus invented from time to time for the manufacture of sheets and pipes; and as he has worked in other interesting matter I make some extracts from it, as some who read this work may not read that.
"Lead can certainly claim a history of no mean length, though it would be impossible to say definitely when it was first used. The Romans, obtaining it in England and Spain, used it to a large extent for water-pipes, using a solder of an alloy of lead and tin.
"Of lead ores the two principal are galena, a compound of lead and sulphur, in the form of sulphide of lead, and cerusite, or carbonate of lead. Galena, by-far the most important and most widely distributed, is of a dark metallic nature, chiefly containing, besides lead, sulphide of silver.
"Of lead mines, perhaps the chief of Great Britain are those of Derbyshire and Cornwall in England, Flintshire in
Wales, Dumfries in Scotland, Wicklow in Ireland, and the Laxey mine in the Isle of Man. In Europe: Carinthia in Austria, Sala in Sweden, the Harz in Germany, those of Saxony, and particularly those in the south of Spain. Lastly, the American mines."
To procure the metal from the galena, the ore is roasted in a furnace under the influence of the oxygen of the air till all the sulphur is burned away and the lead remains.
Through the kindness of one of the largest lead manufacturing houses in the world I am enabled to give an illustration (fig. 1) of one of their reverberatory furnaces in Wales.
Fig. 1. - View of a Reverberatory Furnace.
"At the front and back of the furnace there are three openings, ccc, of the same dimensions, formed by strong cast-iron door-frames, with an inward inclination; these openings are used for raking the ore, to expose as much surface as possible to the influence of the oxygen. At the front of the furnace will be found the tap-hole, b, and at the back of this is the lead-pot, into which the lead is run. In the roof is an opening, a, through which the charge of ore is placed in the furnace from a hopper above. The fire, D, is charged with coal at the back, and cleared at the front. Above and in front of the ash-pit is a flue, e, which carries off any vapour. At the opposite end of the furnace are two rectangular flues, which are connected with a common flue, G, which runs direct to the stack: these flues are provided with dampers, with which they are regulated. Over the brick bottom of the furnace is spread a quantity of grey slags, f f, which act as an excellent furnace bottom.
"The furnace is built of best Buckley fire-bricks, and is braced together with wrought-iron standards and tie-rods. The quantity used to charge the furnace has increased of late years, and is now 29 cwts. of ore [in England, as far as I can ascertain, except in Cornwall, the charge is never so much as this], which is thrown through the hole in the arch by the hopper above. It is then evenly spread over the bed, and frequently, and at times constantly, stirred for about two hours. The furnace temperature is regulated by the damper, and the doors are left partially open in order to admit the requisite quantity of air. At the end of the two hours the grate is cleared from clinker, coal is thrown on the fire, and the damper opened a little so as to expose the charge to a higher calcining heat.
"This operation takes about an hour: more coal is then thrown on the fire, and the doors of the furnace are closed till the charge has melted, which takes about half-an-hour. The doors are again opened, and a few shovelfuls of lime are thrown upon the charge to thicken the unreduced portion, which is then allowed to cool and calcine for an hour. Again the fire is charged, the damper raised, and lime added, till the whole charge of ore is thoroughly melted.
"At the end of eight hours the charge is quite ready to be withdrawn or tapped: the doors of the furnace are opened, the slag thickened with lime, the plug taken out of the tap-hole, and the lead is run out into the lead-pot ready to receive it, and ladled out into pig-moulds. A pig is a piece of solid lead about 2 ft. 3 in. long, 5 in. wide, and 3 in. deep, but it varies in size and shape - of the under side - and therefore in weight, according to the mould of the manufacturer, and may weigh about 1 cwt., l 1/4 cwt., or 1 1/2 cwt.
"Lead is run down into pigs for better transit. Two men are engaged with each furnace, one at the front, the other at the back.
"The ores generally worked in Flintshire furnaces, such as we have described, yield from 75 per cent. to 81 1/2 per cent. of lead per ton of ore. The fumes from the flues are swept out periodically, and worked in the furnaces in conjunction with the ores; they give from 40 per cent. to 50 per cent."
To speak briefly of its properties, pure lead is a pale bluish-grey metal, having the qualities of softness and plasticity in a very high degree, whilst the absence of elasticity is very strongly marked. Under heat it melts at 612° Fahr.; at a bright red heat it emits vapours, and at a white heat it boils. Exposed to ordinary air it becomes tarnished, but the thin film formed increases very slowly. Lead rapidly takes up oxygen with formation of protoxide, which is produced in two forms, massicot and litharge. With respect to the action of water on lead, absolutely pure water has no action on lead by itself, but in presence of pure oxygen it rapidly attacks lead, forming hydrated oxide, which is soluble in water as an alkaline liquid. As all soluble lead compounds are poisons, it follows that lead cisterns and pipes must contaminate pure water; but again, the presence in the water of even small proportions of bicarbonate or sulphate of lime prevents its action on lead, though all impurities by no means act in like manner; for instance, nitrate and nitrite of ammonia intensify the action of water on lead. Acids have little or no effect in the action of water on lead, though the stronger acids - such as nitric acid - have a slowly-taking-place effect which becomes more noticeable if the temperature is raised.