294 



REPORT 1879. 



for the manufacture of the finer varieties of cutlery and edged tools, &c. A brief 

 outline of the process itself is as follows : — The most of the iron employed for this 

 purpose is imported into this country in the shape of bars from Sweden, where it 

 has been smelted from very pure iron ores, in a blast furnace, by the aid of charcoal, 

 and subsequently puddled to free it from impurities. 



The first operation to which it is subjected, is that known as the cementation or 

 converting process, the object of which is to combine a certain quantity of carbon 

 with the iron ; this operation is performed in a furnace of peculiar construction, 

 where the iron and charcoal are packed together in air-tight chests or converting 

 pots, subjected to a high temperature short of the fusing point of iron, where it 

 remains for a matter of three weeks. 



After the conversion, when the pots are cold the bars are taken out and found 

 to be covered with blisters, hence it is termed Blister Steel. In consequence of the 

 various theories proposed to account for this peculiar formation, the writer was 

 induced to make a series of investigations. For this purpose he was kindly fur- 

 nished by Messrs. Seebohm and Dieckstahl of the Dannemora Steel Works, with 

 some samples of this blister steel, various portions of which he submitted to 

 analysis, the results of which showed a marked increase of silicon where the blisters 

 occurred, thus — 



Sample 1. Blister 2 inches in length contained 



2. Small blister contained 



«• » » 



1. Uriblistered portions contained 



*■ >> » >) 



On inspecting one of these bars of blister steel 

 both a physical and a chemical change 



The iron has now assumed a crystalline structure, and has chemically combined 

 with a certain amount of carbon. This latter change commences on the exterior, 

 and extends itself to the interior of the bar, if the process be continued sufficiently 

 long, thus showing that carbonic oxide never penetrates into the centre of the bar, 

 until the whole is converted into steel. 



The writer is indebted to the kindness of the above-mentioned firm for a sample 

 of bar iron, before and after conversion, in order to ascertain the exact chemical 

 change that took place during the process. The following are the results obtained : — 

 Before Conversion After Conversion 



Fe . . . . 99471 98603 



C 

 Si 

 S 

 P 

 Mu 



0-070 per cent, silicon. 

 . 0-048 

 . 0-056 

 . 0-023 

 . 0021 

 . 0025 



it is found that it has undergone 



100-000 



100-000 



The decrease in impurities appears greater than it really is, owing to the fact 

 that the bar itself has increased in weight by the addition of carbon. 



One remarkable fact is that, after the conversion of the iron, a quantity of the 

 charcoal, in the converting pots, is found in a pulverised state, so as to be unfit for 

 further use. 



Some of this waste charcoal the writer has examined, and from one sample, by 

 the aid of a magnet, he succeeded in extracting 5 to 6 per cent, of iron scale and 

 small pieces of steel. These on being treated with dilute hydrochloric acid, evolved 

 considerable quantities of sulphuretted hydrogen ; in one case he estimated the 

 quantity of sulphur - , and found it to contain as much as l - 25 per cent, of this 

 element. The blister steel thus produced, for the sake of convenience is divided 

 into six different classes, viz., 



Spring heat. Country heat. 



Single shear heat. Double shear heat. 



Steel through heat. 



Melting heat. 



