95G 



IRON 



The 'cinders' mentioned in the foregoing Table are not those from tho blast- 

 furnace, but are derived from the cast iron during tho processes of 'refining,' 

 ' puddling,' &c., by -which tho cast iron is converted into wrought iron. Tlu-so 

 cinders are very rich in iron, which exists in (linn principally in the form of silicate 

 of tho protoxide. They often occur beautifully crystallised, particularly .-.in i- they 

 have been calcined : an operation which is always performed on thorn in well-con- 

 ducted works, and which has for its object the removal of tho sulphur and the jx r- 

 oxidation of a portion of the iron. Those cinders, though A-ory rich in iron, aro 

 always contaminated to a considerable extent with both sulphur and phosphorus, as 

 might be expected, seeing that they are the results of operations which have for their 

 objects tho removal of tho foreign matters contained in tho pig-iron. Tho tendency 

 of the former is to make the metal what is called ' hot short,' so that it cannot bo 

 worked while hot under the hammer; tho tendency of the latter element is to make 

 the iron ' cold short,' so that it breaks when an attempt is made to bend it when cold. 

 The separation of sulphur is very perfectly effected by the calcination of tho cinder, 

 and it is interesting to trace the progress of its gradual elimination. In some parts of 

 the heap (which often contains several thousand tons of cinder) largo masses of 

 prismatic crystals of pure sulphur may be found, but usually nearly tho entire surface 

 of the heap is covered with a thin layer of sulphate of iron, sometimes crystallised, 

 but generally in various stages of decomposition ; lower down in tho heap, where the 

 heat is greater, the sulphate of iron disappears, and in its place red oxide of iron, 

 without a trace of sulphur, is found. In calcining a heap of cinders care is required 

 not to allow the heat to rise too high, or immense masses will become melted together, 

 involving the necessity of blasting, which entails much expense. After tho heap has 

 been burning for some months, streams of water are directed over the surface, by 

 which much soluble sulphate of iron is removed. Unfortunately, the process of 

 calcination does not remove any of the phosphoric acid, which necessitates a judicious 

 employment of these cinders in the blast-furnace. Dr. Noad repeatedly submitted 

 forge cinders ' to analysis, and we give in the following Table the average results of 

 his experiments : 



Aiwlyses of Forge Cinders. 



Hot-blast. One of tho greatest improvements ever made by simple means in any 

 manufacture, is the employment of hot air instead of the ordinary cold air of the 

 atmosphere, in supplying the blast of furnaces for smelting and founding iron. Tho 

 discovery of the superior power of a hot over a cold blast in fusing refractory lumps 

 of cast iron was accidentally observed by Mr. James Beaumont Neilson, engineer to 

 the Glasgow Gas Works, about the year 1827, at a smith's forge in that city, and it 

 was made the subject of a patent in tho- month of September in tho following year. 

 No particular construction of apparatus was described by the inventor by which tho 

 air was to be heated, and conveyed to the furnace ; but it was merely stated that tho 

 air may be heated in a chamber or closed vessel, having a fire under it, or in a 

 connected in any convenient manner with the forge or furnace. From this vessel I lie, 

 air is to be forced by means of a bellows into the furnace. Tho quantity of surface 

 which a heating furnace is required to have for a forgo is about 1,260 cubic inches ; 

 for a cupola furnace, about 10,000 cubic inches. Tho vessel may bo enclosed in 

 brickwork, or fixed in any other manner that D n<l desirable, the application 



of heated air in any way to furnaces or forges, for tho purpose of working iron, being 

 the subject claimed as constituting the invention. 



"Whenever a forced stream of air is employed for combustion, the resulting tempo- 



