54 Mr. F. Field on Ludlamite, 



instances the amount of iron was a per cent, or two under the 

 mean of the numbers given above, as estimated by potassium 

 permanganate. In a preliminary note sent to the ' Chemical 

 News ' on this mineral, it was suggested that its probable com- 

 position might be represented by the formula 



3FeO,F 2 5 , 4H 2 0; 

 and in this case the amount of water is 16*7 per cent., within 

 0*3 per cent. of. that in the formula I have adopted ; but the 

 ferrous oxide is lower, and the phosphoric acid higher, than 

 subsequent analyses yielded. In more than ten estimations of 

 iron made from the clear green crystals of the minerals, 40*5 

 per cent, iron was the lowest number obtained. In the analyses 

 of Vivianite, it is well known that the results of chemists have 

 varied much as to the amount of water in the mineral. Vogel, 

 for instance, gives 31*0 per cent., Stromeyer 27*48, and 

 Brandes 25*00 only. Messrs. Maskelyne and Flight found 

 28*26, which agrees best with the recognized formula 

 3FeO, P 2 5 , 8H 2 0. 



Vivianite, on heating, turns white, exfoliates, and does not 

 decrepitate in the slightest, and, moreover, when in the crys- 

 talline form, is oxidized only to a very slight extent. It is a 

 striking experiment to heat small crystals of Ludlamite in the 

 ordinary atmosphere, and another portion in carbonic acid: 

 the decrepitation is the same; but in the former case the crys- 

 tals, as before observed, change their colour to a splendid bluish 

 black, while in the latter atmosphere they become brilliantly 

 pearly white. 



This new mineral I have named Ludlamite, after my friend 

 Mr. Ludlam, a gentleman who for many years has cultivated 

 the science of mineralogy, and possesses, perhaps, the finest 

 private collection of minerals in Great Britain. I have to re- 

 turn my best thanks to Mr. Tailing for having first called my 

 attention to the mineral, and for affording me specimens ne- 

 cessary for its examination. 



I am also extremely indebted to Professor Maskelyne, 

 F.B.S., of the British Museum, who kindly undertook the 

 crystallographic part of the investigation, the results of which 

 are subjoined. 



The crystals of Ludlamite belong to the oblique system, the 

 elements of the crystal being 



101.1 0=42° 24i', 111.0 1 = 36° 21', 



101.0 01 = 37° 2^. 



Otherwise, the angle of the axes Z X is 79° 27', and the para- 



