CLASSIFICATION OF OBJECTS OF INTEREST. 



453 



colour, they will appear to the best advantage upon a black 

 ground. The following list of names will include some speci- 

 mens that are remarkable for the abundance and elegance of 

 form of the animal remains found in them, and others strictly 

 mineral, whose gorgeous colours are only rivalled by the bril- 

 liant plumage of the humming-bird, or by the splendid hues 

 sometimes displayed by polarized light: — 



Biniodide of Mercury, — A very interesting object for the 

 microscope is the recently sublimed deuto-ioduret or bin- 

 iodide of mercury. " This salt, when first sublimed," says 

 Mr. Varley,* " is of a bright yellow colour, which rapidly 

 changes to red ; the manner in which this change takes place 

 being the subject for investigation, and it is well worthy of 

 further attention, as indicating, very probably, the structure 

 of the crystals. To examine them, place a few grains of the 

 deuto-ioduret of mercury in a watch-glass, and invert over it 

 another glass of the same size ; apply the heat of a spirit-lamp, 

 and when fumes issue from between the glasses, remove the 

 lamp, and suflfer the glasses to cool a little ; on removing the 

 upper glass, it will be found lined with yellow crystals, one of 

 which should be rapidly transferred to the stage of the micro- 

 scope for examination as a transparent object; lines of a 

 beautiful red will be seen shooting through the crystal, until 

 it has entirely changed colour: during the time it is changing 

 colour, it will also be seen to change its form. If It be placed 

 on the stage of the microscope very carefully and gently, the 



* Vol. xlix. of the Transactions of the Society of Arts., page 194. 



