262 ANNUAL OF SCIENTIFIC DISCOVERY. 



of iron. Practice and experience will, no doubt, in time enable the workman 

 so to regulate the operation as to produce to a nicety any particular quality 

 of iron or steel required ; but until this practical knowledge has been gained, 

 there will be some difficulty in calculating the exact length of time to be occu- 

 pied in the conversion. If, therefore, the process should be continued a little 

 too long for steel, malleable iron will be obtained if it be continued a little too 

 long for malleable iron, the metal will be set in the furnace. The " boil" appears 

 to be the critical period. "Whatever be the time occupied in arriving at the 

 boil, it is found that from 12 to 15 minutes are requisite to produce malleable 

 iron, and from 7 to 12 minutes to produce the different qualities of steel. 



How effectually the carbon can be removed is shown by an analysis of a 

 chance specimen of Mr. Bessemer's malleable iron, made by Dr. Henry, who, 

 we believe, was strongly inclined to doubt whether the process could really be 

 as successful as it was stated to be. He found the quantity of carbon present 

 to be less than l-30th per cent. or less than l-3000th part of the weight of 

 the metal. Of silica, a trace merely was found. By the application of means 

 already well understood, the sulphur and phosphorus will be as completely 

 removed. A considerable portion of both is driven off without the use of any 

 means for that special object ; and by treating the melted metal with proper 

 substances, these impurities will be withdrawn. The difficulty which Mr. 

 Bessemer has applied himself to solve, and which he has solved, is the com- 

 plete separation of carbon and the earthy bases. Apart from the cheapness 

 and facility of his process, he has been able successfully to grapple with the 

 half per cent, of carbon which puddling can never get rid of. 



The process, as described above, is open to a serious objection. The blast 

 must be kept up to the last, or the melted metal would run into the tuyeres, 

 and spoil the blast apparatus. Hence the air is being driven through the 

 metal up to the very moment that it ceases to run out of the vessel ; and the 

 ingots produced are consequently very porous and full of air bubbles. "With 

 malleable iron, this is of no importance, as it would always be rolled while in 

 a state not far from fusion, and the air would be completely squeezed out, as 

 the slag is squeezed out of the p-uddled ball. But cast steel would be useless 

 if porous a difficulty which is met by an ingenious modification of the con- 

 verting vessel. It is slung horizontally at the end of two cranks, which, by 

 means of a counterbalancing weight, can easily be turned through any angle. 

 The blast is admitted by a pipe passing through the axle of one of the cranks, 

 and thus revolving with the converting vessel. The tuyeres enter the con- 

 verting vessel by a series of apertures forming a horizontal row. The cylinder 

 can thus be made to revolve round the axis of the crank without turning upon 

 any axis of its own ; and thus the apertures of the tuyeres may be raised till 

 they are brought above the surface of the metal. The blast can then be 

 turned off and the agitation of the metal allowed to subside. Iron melted by 

 existing processes sets in about three or four minutes, but Mr. Bessemer finds 

 that he can allow it to stand for ten or twelve minutes a period quite suffi- 

 cient to allow all the air bubbles to escape and the cylinder may then be 

 raised still further, ancl the metal poured off as gently as may be requisite, 

 through a spout at the top or in the side of the vessel. 



