?00 Effects of Heat modrfied ly Compression. 



that being the arnioml badge of the place in Siberia where 

 this iron i? made *. 



A woiknian explained to me some of the properties of 

 liifFerent kinds of iron?, most interesting in my present pur- 

 suit; and he illustrated what he said by actual trial. All 

 iron, when exposed to a certain heat, crushes and crumbles 

 under the hammer ; but the temperature in which this hap- 

 pens, varies with cverv different species. Thus, as he showed 

 me, cast iron crushes in a dull red heat, or perhaps about 

 IS'^ of Wedsewood'; steel in a heat, perhaps, of 30"; Swe- 

 dish iron, in a briglit white heat, perhaps of 50° or 6o**; 

 old sable itself likewise yields, but in a much higher heat, 

 perhaps of -Ifi^^V'-- 1 merely guessed at these temperatures; 

 but I am certain of this, that in a heat similar to that in 

 which Swedish iron crumbled under the hammer, the old^ 

 .sable withstood a strong blow, and seemed to possess con-- 

 siderable -fimmess. It is from a knowledge of this quality 

 that the'blacksmith, when he first takes his iron from the 

 forge, aii^ lavs it on the anvil, begins by very gentle blows, 

 till the tem|^t;rature has sunk to the degree in w'hich the iron 

 can bear the hammer. I observed, as the strong heat of the 

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

 surface, clearly indicating the discharge of some gaseous" 

 matter; whereas, the old sable, in the same circumstances, 

 acquired the shinina" surface of a liquid, and melted away 

 without any effervescence. I procured, at this time, a con- 

 siderable naiDber of bar^ of that iron, which fully answered 

 mv expectations. 



By the experiments last mentioned, a very important 

 point was gained in this investigation ; the complete fusi- 

 bility of the carbonate laKlcr pressure being thereby esta- 

 blished. But from this very circumstance a necessity arose 

 of addins; some new devices to those already described : for 

 the carbonate, in fusion, spreading itself on the inside of the 

 tube containing it, and the two uniting firmly together, so 

 as to be quite inseparable, it was impossible, after the ex- 

 periment, to ascertain the weight of the carbonate by any 



* I was f.»'ourcd witli this account of it by llie late professor Robison. , 



iivcthod 



