396 
Cast Steel • 
greater or less degree the qualities of fusibility, brittle, 
ness, and hardness ; he also showed that the same effects 
may be produced by fusing bar iron with glass and char* 
coal, or the black o xide of iron with the requisite propor- 
tion of charcoal alone, or by keeping in fusion for about 
the space of an hour a mixture of small bits of iron and 
equal parts of clay and marble or any otfter calcareous 
carbonat. In 1800, Mr. Mushet took out a patent for 
preparing cast steel of various qualities by fusing bar iron 
with different proportions of charcoal, coinciding (?) for the 
most part with the facts and principles before laid down 
by Clouet, and confirmed by his own experiments ; but 
whether the steel thus prepared is equal to the finest cast 
steel of Huntsman, has not, we believe, been as yet com- 
pletely ascertained. 
Steel is rendered hard by heating and then suddenly 
cooling it. The degree of hardness which it is capable 
of acquiring is in direct proportion to its fusibility, or in 
other words to the quantity of carbon with which it is 
combined ; and the degree of hardness which in any parti- 
cular instance is actually given to it, is in proportion to the 
difference of temperature between the medium in which 
it is heated and that in which it is cooled ; modified how- 
ever by the capacity for heat, and the conducting power 
of the cooling medium. Thus if steel is heated some- 
what below the degree at which it melts and then trans- 
ferred into oil at the temperature of 200 , the hardness 
thus acquired will be inferior to that which would 
have been obtained if water, or still more so if mercury, at 
the same temperature had been made use of. Again, if 
instead of oil at 200° the same fluid at 400° had been em- 
ployed, a greatly superior degree of hardness would have 
been produced. 
The hardness acquired by this method has generally 
been thus accounted for. The particles of the metal by 
