^6 Observations on Iron and Steel. 



place of the folid angles, and which are fubject to another 

 law of decreafe, to be fpoken of hereafter. 



If the decreafe of the laminse of fuperpofition took place- 

 according to a more rapid law j if each lamina for examplfc 

 had had on its circumference two, three, or four ranges of 

 cubes lefs than the inferior range, the pyramids produced 

 around the nucleus, by this decreafe, being more lowered, 

 and their adjacent faces being no longer on a level, the fur- 

 face of the fecondary folid would be compofed of 24 ifofceles 

 triangles, all inclined one to the other. I call decreafe on the 

 edges that which takes place parallel to the edges of the nu- 

 cleus, as in the preceding examples, to diftinguifli it from 

 another kind of decreafe which I (hall fpeak of hereaftef, 

 and which takes place according to directions altogether 

 different. 



(To be continued.) 



XI. Observations on Iron and Steel. By JOSEPH COLLIER* 

 From the Tranfaclions of the Manchefter Society. 



[With a PIate } No.lll.~\ 



XA.FTER examining the works of different authors who 

 have written on the fubject of making iron and (reel, I am 

 perfuaded that the accounts given by them of the neceffary 

 procefTes and operations are extremely imperfect. Chemifts 

 have examined and defcribed the various compound mine- 

 rals containing iron with great accuracy, but have been lefs 

 attentive to their reduction. This obfervation more parti- 

 cularly applies to fteel, of the making of which I have not 

 feen any correct account. It is Angular to obferve how very 

 imperfectly the cementation of iron lias been defcribed by 

 men of great eminence in the fcience of chemiftry. Four- 

 croy ftates the length of time neceffary for the cementation 



of 1 



