1036 



ITACOLtTMITE 



solution of isinglass covered with carmine forms an excellent injection-liquor to the 

 anatomist. M. Eochen has made another pretty application of isinglass. Ho 

 plunges into a limpid solution of it, made by means of a water-bath, sheets of wire- 

 gauze set in window- or lamp-frames, which, when cold, have the appearance of glass, 

 and answer instead of it for shades and other purposes. If one dip be not sufficient 

 to make a proper transparent plate of isinglass, several may bo given in succession, 

 allowing each film to harden in the interval between the dips. The outer surface 

 should be varnished to protect it from damp air. These panes of gelatine are now 

 generally used for lamps instead of horn, in the maritime arsenals of France. See 

 GELATINE. 



Isinglass is known commercially as Leaf Isinglass, Long and Short Staple, and 

 Book Isinglass. Dr. Eoyle speaks of the Samovey leaf, *book, and long and short 

 staple, in his paper On the Production of Isinglass along the coasts of India, with 

 a Notice of its Fisheries. We receive from the Brazils, Pipe, Lump, and Honeycomb 

 Isinglass. 

 , Our Importations of isinglass in 1871 and 1872 were : 



XSOMERISM, from tffos, equal, and nfyos, part. Identity of elements and 

 proportions with variations in physical properties. Thus, oil of turpentine and oil 

 of citron are isomeric, each having the composition C 20 H 16 (C 10 H 16 ). The study of 

 the laws of atomic constitution is one of the most important within the range of 

 physico-chemical science, and, beyomd all others, it demands the highest powers 

 of the philosopher, united with the mechanical care of the microscopic analyst. 

 The tendency of science leads to the conviction that many of the bodies which we 

 now regard as distinct elements are only isomeric ; and such groups as chlorine, 

 iodine, bromine, and fluorine, as sulphur, selenium, and boron, and as carbon and 

 silicon, may, with the advance of our knowledge, be shown to be modified conditions 

 of one form of matter. 



Several groups of isomeric bodies may be recognised, namely : isomeric, properly so 

 called, when compounds have the same percentage composition, and exhibit analogous 

 decompositions ; metameric, when compounds have the same percentage composition, 

 but do not exhibit analogous decompositions under similar circumstances ; and pcly- 

 meric, when compounds have the same percentage composition, but different molecular 

 weights. 



The subject of Isomerism is fully treated in Watts's ' Dictionary of Chemistry.' 



ISOMORPHISM. Mitscherlich was the first to observe that many groups of 

 substances, simple or compound, having an analogous constitution, crystallise in forms 

 of the same crystalline character, or differ but little in their angles. Thus, alumina, 

 red oxide of iron, and sesguioxide of chrome crystallise in forms of the rhombohedral 

 system. 



Carbonate of lime, carbonate of magnesia, carbonate of iron, and carbonate of man- 

 ganese, are also isomorphous forms, belonging to the rhombohedral system. 



Sulphate of baryta, sulphate of strontia, and sulphate of lead, crystallise in isomor- 

 phic forms of the prismatic system. 



For a development of this law, consult Brooke and Miller's ' Mineralogy,' Dana's 

 ' System of Mineralogy,' and ' Watts's Dictionary of Chemistry.' 



ISOPTTRPURATE OF AMMONIUM. See MUKKXIDK. 



ZTABIRITE. A rock composed of specular iron ore (micaceous iron) and quartz. 

 It takes its name from Itabira, in Brazil, where it often accompanies the occurrence 

 of gold. 



ITACOLUMITE. A fine-grained schistose rock, composed mainly of quartz, 

 with more or less mica, talc, or chlorite. Some varieties are flexible when in thin 



