342 Dr. Pearson's Experiments 
rieties are reckoned to be those of wrought iron. The carbon 
may however be in such proportion as to produce a state of 
iron, which in some degree possesses the properties both of 
steel, and wrought iron ; or which possesses partly the proper- 
ties of steel, and partly the properties of wrought iron. It is 
quite arbitrary to call such kinds of iron, steel or wrought 
iron. 
There are also innumerable varieties of the second state of 
iron explained, viz. steel. Some of these are known and dis- 
tinguished by artists. A greater, or 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 pro- 
perties of steel. 
Besides these varieties of iron and steel depending upon car- 
bon, there are other varieties from extraneous substances of a 
different nature. These are most frequently oxide of iron, or 
oxygen, and silica ; especially in steel from the ore. The pre- 
sence 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 contain manga- 
nese ; as the fine experiments of Professor 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 
