168 IMr. Mallet on the Physical Conditions 



"In Sweden they remedy this difficulty in the following way: — the charge 

 for the furnace is made up partly of roasted ore and partly of raw ore, and the 

 furnace is so kept in blast that its yield shall be regular, and the slag good 

 (i. e. nearly colourless). There is thus obtained a pig-iron, very closely mottled, 

 made up of white lamellar iron, and of dark gray iron, like the usual mixed 

 qualities of pig-iron. It is obvious that these two sorts of ores, having two 

 different degrees of fusibility,' are reduced after diflFerent periods in the furnace, 

 and hence afford, one of them gray, and the other white iron. If the minerals 

 be properly proportioned, there is obtained a very finely mottled gray iron, 

 which is less porous, harder, and more tenacious than the gray irons obtained by 

 the ordinary methods [of mixture, namely on remelting in the cupola]." 



He then proceeds to describe another method of working the blast furnace, 

 by which similar results may be obtained, and concludes: — "By these means 

 we may determine to pig-iron any proportion of carbon we please ; the 

 metal becomes more tenacious, expels less graphite [in cooling, namely], 

 and never shows spongy cavities after cooling." — Karsten, Handbuch der Eisen- 

 huttenkunde. (Note I.) 



61. M. Kulmann, also, in his Lectures on the Manufacture of Projectiles, &c., 

 for the Artillery School of Metz, gives a precisely similar account ; in a word, to 

 obtain the very finest quality of cast-iron for gun-founding, all that is necessary 

 is the use of a small-sized blast furnace, such as those occasionally found in 

 Staffordshire, a very gentle blast, and a heavy charge of ore and flux, in the 

 mixed form above directed. A low temperature must be preserved in the 

 furnace ; — the production of dark gray, graphytic iron resulting always from 

 intensity of heat. 



62. The use of charcoal in place of pit-coal, or coke, does not appear essen- 

 tial. Many "makes" of British iron, smelted with sulphur-bearing 'coal, yet afford 

 no sensible traces of sulphur on analysis ; its exclusion being always capable of 

 being insured by a proper mode of working the furnace, while the recent 

 researches of M. Janoyer, Director of Iron Works in the south of France, appear 

 to indicate that by the judicious use of a certain proportion of phosphatic ores, 

 along with our ordinary clay ironstones, sulphur may be completely eliminated 

 from the iron, the sulphur being replaced permanently by phosphorus, and 

 going off as sulphuret of carbon. 



63. Neither does the use of cold blast appear indispensable, although greatly 



