INTRODUCTION. XXXV'h 



iron, which is found even in the most transparent, the calca- 

 reous spar of Iceland ; ee and it may be said in general that 

 all minerals contain that metal."* 



To these eminent testimonies may be added Kirwan, who Kirwan. 

 has nearly approached to this division ; for, after describing 

 the simple earths, he proceeds as follows : 



"" Calces of Iron. To these simple earths we must also 

 annex the consideration of calces of iron, as they almost 

 always accompany earthy or stony substances, are mixed or 

 combined with them, and are the source of many both of 

 their external appearances and internal properties. 



" Calces of iron are formed of iron, combined with dif- 

 ferent proportions of pure air, and frequently of water also, 

 and fixed air. 



" One hundred parts metallic iron are capable of taking 

 up 66 or 70 of pure air. When 100 parts iron contain but 

 40 of this air, the compound is still magnetic, "f 



In another place, after observing that any earth which 

 forms less than one twentieth of a compound, is seldom of 

 any importance, he proceeds to state that calces of iron in- 

 fluence in some measure the properties of a compound, even 

 when they do not exceed one thirty- third part of the whole, 

 that is, three in the hundred - 3 and if they be themselves 

 magnetic, they communicate that property to compounds of 

 which they form above one tenthf . 



In a later production, and with more ample information, 

 he presents the following remarks. ' ' The proportion of the 

 different materials contained in the chaotic fluid to each 

 other, may be supposed upon the whole nearly the same as 

 that which they at present bear to each other $ the siliceous 

 arth being by far the most copious -, next to that, the fer- 



* Fr. tr. 1792, i. 170. ii. 378. 



f- Min. i. 17. Calces were powders, now called oxyds. Thomson, i. 132. 



1 Ib. p. 48. In his treatise on the Magnet (Mem. R. I. A. vi.), Mr. Kir- 

 wan says that iron abounds in all minerals, from 2 to 25, but at a medium 6. 

 This globe, he adds, is 4.5 heavier than water; and, p. 182, thinks the centre 

 iron; and afterwards calls it a great magnet, in which Hauy coincides. 



