322 



THE MICROSCOPE AND ITS REVELATIONS. 



exhibiting a series of tertiary tints. 1 The following List specifies the 

 Salts and other substances whose crystalline forms are most interesting. 

 When these are viewed with Polarized light, some of them exhibit a beauti- 

 ful variety of colors of their own, whilst others require the interposition 

 of the Selenite plate for the development of color. The substances 

 marked d are distinguished by the curious property termed dichroism, 

 which was first noticed by Dr. Wollaston, but has been specially investi- 

 gated by Sir D. Brewster. 2 This property consists in the exhibition of 

 different colors by these crystals, according to the direction in which the 

 light is transmitted through them; a crystal of Chloride of Platinum, 

 for example, appearing of a deep red when the light passes along its axis, 

 and of a vivid green when the light is transmitted in the opposite direc- 

 tion, with various intermediate shades. It is only possessed by doubly- 

 refracting substances; and it depends on the absorption of some of the 

 colored rays of the light which is polarized during its passage through 

 the crystal, so that the two pencils formed by double refraction become 

 differently colored, the degree of difference being regulated by the in- 

 clination of the incident ray to the axis of double refraction. 



Acetate of Copper, d 



of Manganese 

 of Soda 



of Zinc 



Alum 



Arseniate of Potass 



Asparagine 



Aspartic Acid 



Bicarbonate of Potass 



Bichromate of Potass 



Bichloride of Mercury 



Binoxalate of Chromium and Potass 



Bitartrate of Ammonia 



of Lime 



of Potass 



Boracic Acid 

 Borate of Ammonia 

 of Soda (borax) 



Carbonate of Lime (from urine of horse) 

 Carbonate of Potass 



of Soda 



Chlorate of Potass 

 Chloride of Barium 

 of Cobalt 



of Copper and Ammonia 



of Palladium, d 



of Sodium 



Cholesterine 

 Chromate of Potass 

 Cinchonoidine 

 Citric Acid 

 Cyanide of Mercury 

 Hippuric Acid 

 Hypermanganate of Potass 

 Iodide of Potassium 



of Quinine 



Mannite 

 Margarine 



Murexide 



Muriate of Ammonia 



Nitrate of Ammonia 



of Barytes 



of Bismuth 



of Copper 



of Potass 



of Soda 



of Strontian 



of Uranium 



Oxalic Acid 

 Oxalate of Ammonia 



of Chromium 



of Chromium and Ammonia, d 



of Chromium and Potass, d 



of Lime 



of Potass 



of Soda 



Oxalurate of Ammonia 

 Phosphate of Ammonia 



: Ammoniaco-Magnesian (triple 



of urine) 



of Lead, d 



of Soda 



Platino-chloride of Thallium 

 Platino-cyanide of Ammonia, d 

 Prussiate of Potass (red) 



Ditto ditto (yellow) 

 Quinidine 

 Salicine 

 Saliginine 

 Saiitonine 

 Stearine 

 Sugar 



Sulphate of Ammonia 

 of Cadmium 



of Copper 



- of Copper and Ammonia 



1 ' On the Employment of Colloid Silica in the preparation of Crystals for the 

 Polariscope,' in " Monthly Microscopical Journal," Vol. v., p. 50. 



2 " Philosophical Transactions," 1Q1ft 



1819. 



