91 



TAB. CCCL. 



FERRUM sulpbatum. 

 Sulphate of Iron. 



Div. 2. Imitative. 



The upper specimen is a remarkably fine Stalactite from 

 Cornwall, and has been in my possession many years 

 without having apparently undergone any alteration, which 

 is seldom the case. I have shown specimens in Plates 23 

 and 28 which have a very different appearance. It is 

 commonly called Green Martial Vitriol, is usually soluble 

 in twice its weight of cold water, and less than its weight 

 of boiling water. It is said to have a double refracting 

 power in proper and transparent Crystals. It is used for 

 making ink with oak-galls, and gives it a peculiar astrin- 

 gent taste. It produces black with any vegetable, and is 

 a styptic. The specimen figured above has some signs of 

 the primitive rhomboidal angles about it. 



The lower Jigure is taken from a North Wales specimen : 

 it is more apt to decompose, and shows the changes it un- 

 dergoes under these circumstances, as it becomes yellow or 

 brown, sometimes crumbling into a Sulphur yellow* The 

 primitive Crystal is somewhat apparent about this specimen; 

 but the lowest Jigure is most perfect in that respect; such is 

 sometimes found in Cornwall and Derbyshire. Dr. Kidd 

 mentions finding it in the Shale that overhangs Odin mine 

 at Castleton in the latter county. Sulphate of Iron is often 

 of a fair green colour, (see Elucidation of Colours) lighter 

 or darker, by which it is known from Zinc, which is nearly 



