FORMATION OP CRYSTALS. 



729 



shown on a red selenite ground. Crystallisation under a 

 somewhat different condition and combination is seen in 

 the New Eed Sandstone, No. 158. 



The prismatic rings of another crystalline substance, 

 Quartz, represented in No. 159, possess great interest. 

 Again, that of Arragonite, Tremolite, and Carbonate of 

 Lime. The latter is frequently seen in combination with 

 animal structure, and is then productive of many re- 

 markable changes and modifications, such as we have 

 represented in Plate VIII. Nos. 171, 172, 175, and 180, 

 all of which should be prepared for examination with as 

 well as without the polariscope. 



The formation of artificial crystal may be readily 

 effected, and the process watched, under the microscope, by 

 simply placing a drop of a saturated solution of any salt 

 upon a previously warmed slip of glass. The following 

 list of salts and other substances form a beautiful series 

 of objects for polarised light : — 



Alum. 

 Asparagine. 



Aspartic Acid. Plate VIII. No. 168. 

 Bitartrate of Ammonia. 

 Boracic Acid. 



Borax. Plate VIII. No. 164. 

 Carbonate of Lime. 

 ,, Soda. 



Chlorate of Potash. 

 Chloride of Barium. 

 Cobalt. 

 ,, Copper and Ammonia. 



,, Sodium. 

 Cholesterine. 

 Chromate of Potash. 

 Cinchonine. 

 Cmchonidine. 

 Citric Acid. 

 Hippuric Acid. 

 Iodide of Mercury. 



,, Potassium. 



,, Quinine. 

 Iodo-disulphate of Quinine. 

 Murexide. 

 Nitrate of Bismuth. 



,, Barytes. 



,, Brucine. 



„ Copper. 



,, Potash. 



,, Strontian. 



,, Uranium. 

 Oxalate of Ammonia. 



„ Chromium. 



,, Chromium and Potash. 



„ Lime. 



„ Soda. 



Oxalic Acid. 



Oxalurate of Ammonia. 



Permanganate of Potash. 



Phosphate of Lead and Soda. 



Platino-cyanide of Magnesia. 



Plumose Quinidine. 



Prussiate of Potash, red and yellow. 



Quinidine. 



Santonine. 



Salicine. 



Salignine. Plate VIII. No. 162. 



Sulphate of Cadmium. 



,, Copper. 



„ Copper and Potash. 

 Sulphate of Iron. 



„ Iron, Cobalt, and Nickel 



,, Magnesia. 



„ Nickel and Potash. 



,, Soda. 



,, Zinc. 



Sugar. 



Tartaric Acid. 

 Thionurate of Ammonia. 

 Triple Phosphate. 

 Urate of Ammonia. 



,, Soda. 

 Urea, and all the urinary deposits. 

 Uric Acid. 



MINERALS. 



Agates, various. 

 Asbestiform Serpentine. 

 Avanturine. 

 Carbonate of Lime. 

 Carrara Marble. 



