248 On the Air-Furnaces employed in Iron Foundries. 



bottom formerly defcribed as being appropriated for its recep- 

 tion. The door is again clofed and made air-tight, and the 

 operation of firing continued with unremitting care and at- 

 tention. 



The time of melting depends entirely upon the quantity of 

 metal introduced. The furnaces defcribed above are capable 

 of melting from 50 to 60 hundred weight of metal each, and 

 when there is a moderate circulation of air they will perform 

 this work in 2^ or 3 hours. In half an hour after the metal 

 is introduced it allumes a blackifli red colour. It then 

 begins to brighten with every additional fire, and in about 

 one hour appears white, and begins to lofe (liape, and refem- 

 ble a wreath of fnow. 



An eye accuftomed to fuch heats will now difcern the 

 metal beginning to drop, and run down the inclined plane 

 in very beautiful ftreamlets refembling quickfilver. Eight or 

 ten of thefe are vifible at a time, and after proceeding half 

 way down begin to form jun6lions with each other, and flow 

 connefted into the general cavity or refervoir. By-and-by 

 this becomes filled, and literally forms a beautiful molten 

 mirror, in which fometimes part of the interior furnace is 

 refie£led. 



The furnace-man, by fearching at the bridge with his fire- 

 iron or teafer, judges when the metal is nearly all gone. Of 

 this he is certain by looking up from the peep-hole of the 

 lading-door. If the ftreamlets of the running aietal have 

 ceafed, then the whole is melted, and ready for running out. 



In the operation of melting, the three following circum- 

 ilances ought to be particularly attended to : the thinnefg 

 or hotnefs of the metal ; the wafte or lofs fuftained in melt- 

 ing; and the quantity of coals employed. 



The firft is of the utmoft importance, as many articles in 

 the foundry bufinefs require the metal in a ftate of the greateft 

 divifion ; othcrwife they will be found imperfeft when taken 

 from the fand, and unfit for fale. The furnace-man, there- 

 fore, is always on the watch to replace the fire as it decays, 

 and keep a large and fliarp volume of iiame conftantly pafiing 

 over the metal. 



The wafte or lofs of real metal is alfo an obje£l of great 

 importance. This always bears a relation to the quality of 

 the iron, the ftrength and cleannefs of the coals, and the 

 judgment and attention of the melter. Strong iron is found 

 always more diificult to fufe; this neceflarily expofes it for a 

 long period in contain with the flame. The reverfe happens 

 with metal that is more fragile, and eafier broken in the pig. 

 The length of the expofure in fufing depends on this ; and 



other 



