MODIFIED by COMPRESSION. IfI 
above an inch fquare, made me very anxious to obtain barrels 
of the fame fubftance, which being made of greater fize, ought 
‘to afford refults of extreme intereft. I found upon inquiry, 
that this barrel was not made of Swedith iron, as I at firft fup- 
pofed, but of what is known by the name of O/d 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 worKmaAn explained to me fome of the properties of diffe- 
rent kinds of irons, moft interefting in my prefent purfuit ; 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 fhewed me, caft iron cruthes 
in a dull-red heat, or perhaps about 15° of WerpGwoop ; 
fteel, in a heat perhaps of 30°; Swedifh iron, in a bright 
. white heat, perhaps of 50° or 60°; old fable, itfelf, likewife 
yields, but in a much higher heat, perhaps of 100°. I merely 
gueffed at thefe temperatures ; but I'am certain of this, that ina 
heat fimilar to that in which Swedifh iron crumbled under the 
_ hammer, the old fable withftood a ftrong 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 Swedish 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 circumftances, acqui- 
red the fhining furface of a liquid, and melted away without 
any effervefcence. I procured, at this time, a confiderable 
' number 
~* T was favoured with this account of it by the late Profeffor Rozison. 
