MODIFIED by COMPRESSION. m 



above an inch fquare, made me very anxious to obtain barrels 

 of the fame fubftance, which being made of greater fize, ought 

 to afford remits of extreme intereft. I found upon inquiry, 

 that this barrel was not made of Swedifh iron, as I at firft fup- 

 pofed, but of what is known by the name of Old Sable , from 

 the figure of a Sable ftamped upon the bars ; that being the 

 armorial badge of the place in Siberia where this iron is 

 made *. 



A workman explained to me fome of the properties of diffe- 

 rent kinds of irons, molt interefting in my prefent purfuit 5 and 

 he illuftrated what he faid by actual trial. All iron, when expo- 

 fed to a certain heat, crufhes and crumbles under the hammer ; 

 but the temperature in which this happens, varies with every 

 different fpecies. Thus, as he mewed me, call iron crufhes 

 in a dull-red heat, or perhaps about 15 of Wedgwood ; 

 fteel, in a heat perhaps of 30 ; Swedifh iron, in a bright 

 white heat, perhaps of 50° or 60 9 ; old fable, Itfelf, likewife 

 yields, but in a much higher heat, perhaps of ioo°. I merely 

 gueffed at thefe temperatures ; but I am certain of this, that in a 

 heat fimilar to that in which Swedifh iron crumbled under the 

 hammer, the old fable withflood a flrong blow, and feemed to 

 poffefs confiderable firmnefs. It is from a knowledge of this 

 quality, that the blackfmith, when he firft takes his iron from 

 the forge, and lays it on the anvil, begins by very gentle 

 blows, till the temperature has funk to the degree in which the 

 iron can bear the hammer. I obferved, as the flrong heat of 

 the forge acted on the Swedifh iron, that it began to boil at the 

 furface, clearly indicating the difcharge of fome gafeous mat- 

 ter ; whereas, the old fable, in the fame circumflances, acqui- 

 red the mining furface of a liquid, and melted away without 

 any effervefcence. I procured, at this time, a confiderable 



number 



* I was favoured with this account of it by the late Profeffor Robison. 



