304 On the Cw-ponent Parts of Iron-jlanes, 



fition of the ignited c;a» ; and, as the laft portions of the acid 

 and water arc diiti'ilino-, the ftoae is apt to gain weight by the 

 calcination (oxygenation) of its iron. This will pofitively be 

 the cafe when the heat is carried bevond the neceffary degree, 

 and is indicated by the iron-done fwellingin bulk, becoming 

 fpecifically lighter and porous on the furface, but gaining 

 ^weight in a great degree internally. As oxygenation goes 

 on, the magnetic virtue decreafes, until at laft it becomes 

 entirely annihilated. 



The firft ftage in torrefa&ion is indicated by the firft 

 general change of colour in the iron-ftone. This is com- 

 monly a faded blood colour, more or lefs dark according 

 to the quantity of lime prefent. 



I have repeatedly made ufe of all the various iron-ftones, 

 in the ftate of a fine powder, in order to afcertain what was 

 the weight loft by each clafs in its tranfition from its native 

 hue to the firft ftage of an aflumed colour. And I am 

 enabled to ftate the following as an average of the refults 

 obtained on this head: Calcareous iron-ftones give out 6 

 parts in ioo of the raw mineral; argillaceous iron-ftones, 5; 

 and filiceous iron-ftones, 4'-. 



If the pulverifed iron-ftone is thrown into a vefiel red 

 hot, this lofs will be effected in two minutes. The change 

 of colour is immediately effected on thofe parts in contact 

 with the heated iron. The whole is brought into contact 

 with it; and when thrown out, the magnet will be found 

 to have acquired a perceptible influence over it. When the 

 powder is firft thrown in, a flight decrepitating noife is 

 heard for a few feconds. This operation may alfp ferve to 

 {hew the prefence of fulphur, or of its acid. When in the 

 former ftate it inftantly takes fire, and burns with a dark 

 lambent flame. When the acid is prefent, it is eafily 

 known by the fuffocating fumes difengaged by the action 

 of heat. 



The application of heat beyond the firft flagc of colour, 

 eaufes the iron-ftone to pals through a variety of {hades, 



Thefe A 



