VOL. LXXXV.] PHILOSOPHICAL TRANSACTIONS. SQl 



smaller proportion of carbon, than the quantity requisite to saturate the iron, is 

 the cause of these varieties : which are reckoned varieties of steel, because they 

 possess in certain degrees the distinguishing properties of steel. 



Besides these varieties of iron and steel, depending on carbon, there are other 

 varieties from extraneous substances of a different nature. These are most fre- 

 quently oxide of iron, or oxygen, and silica ; especially in steel from the ore. 

 The presence of phosphoric acid has been shown to be the occasion of the 

 variety of iron, named cold short ; which is brittle when cold, but not when 

 ignited. And there is another variety called red short, which is malleable when 

 cold, but brittle when ignited; the cause of which is supposed to be arsenic. Iron 

 and steel may contain an extraneous substance, and yet possess the properties of 

 good, or even the best kinds of these metals: for this is the case when they con- 

 tain manganese ; as the fine experiments of Professer Gadolin, made under the 

 direction of Bergman, have demonstrated. There are states of iron which are 

 mechanical mixtures of steel and wrought iron. This is more or less always the 

 case with bar steel, made by cementation. If the bar be thick, the interior part 

 will be mere iron. 



Lastly. There are different sorts of steel and wrought iron, from the differ- 

 ence of mechanical arrangement of their parts. So the specific gravity of steel by 

 cementation may be increased by fusion, or hammering, and its grain altered. I 

 have been told, that it may be hammered in the cold till it is so brittle that a 

 slight stroke will break a thick bar. By quenching close-grained hammered steel 

 in cold water, when ignited to whiteness, its specific gravity is diminished, its 

 grain is opened, and it is rendered much harder. These distinctions will per- 

 haps serve to explain the nature of many varieties of the different states of iron, 

 differently named by artizans, namely, pig-iron ; charcoal, and coal pig, or sow 

 iron ; blue, gray, white cast iron ; — soft iron ; tough iron ; brittle iron ; hard 

 iron ; — ore steel ; cement steel; blister steel ; soft steel ; hard steel ; hammered 

 steel ; cast steel ; burnt steel ; over cemented steel. 



I shall next endeavour to show to which of the above states of iron the wootz 

 is to be referred, or to which of them it most approximates. It appears that 

 wootz is not at all malleable when cold ; and when ignited it is difficultly forged 

 and only in certain degrees of fire. It can be tempered and distempered, but 

 not to a considerable extent of degrees (§ 3. e, f.) The range of degrees of fire 

 at which it is forged is of less extent (^ 3. and § 3. b.) than the degrees at which 

 it can be tempered, (§ 3. and ^ 3. e, f.) It vies with the finest steel in its polish. 

 Its specific gravity, which is less than that of hammered iron, is very little di- 

 minished by ignition and cooling rapidly (§ 2. N° 6.) It melts, but at a higher 

 temperature than crude iron (§ 3. h, i). It is not easily reduced into filings, 

 even after annealing (§ 3. f.) Its polished surface grows black by being wetted 



