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252 OXIDES, EARTHS, AND ACIDS. yhite. Some varieties exhibit a beautiful play of colours. Very brittle. H =S*5...6'5. G = 1*9...2*3, The variety called hyalite is transparent...semitransparent; colourless; reniform, botryoidal. Eire opal is transparent; red, yellow, sometimes iridescent. Noble opal, semitransparent... translucent; milk-white, yellowish-white, exhibiting a play of colours. Common opal shows no play of colours. Semiopal is dull and opaque. Cascholong is white and opaque. Siliceous sinter is deposited in fibrous, reniform and botryoidal masses by various hot springs. Hyrophane imbibes water readily, and becomes more transparent in consequence. In the matrass yields water. Before the blowpipe decrepi tates, is infusible. Is almost perfectly soluble in a cold solu tion ot caustic potash. In other respects, the chemical charac- ters are the same as those of quartz. Consists of amorphous silica with from 6 to 13 per cent ot water, and small quantities of red oxide of iron, alumina, nme, magnesia, potash and soda. Analyses of hyalite a from Frankfort on tho Maine by Bucholz, b from Hungary by Beudant, <? from Waltsch in Bohemia by Schaffgotsch, of the red or yellow variety called fire opal d from Zimapan in Mexico by Klaproth, of noble opal, exhibiting a play of colour e from Cscherwenitza in Hun gary, of yellow opal /from Telkobanya, both by Klaproth « b c d e f Silica. . . . 92-00 91-32 95-5 92’00 90'0 93'6 Bed oxide of iron. — — 0 -8 o-26 — ro Lime ..... — — 0*2 Water .... e -33 8-»8 30 7-75 io-o 5-0 In hyalite from Zimapan in Mexico the loss by ignition was iound to be 2-6...2-9 per cent.; in siliceous sinter from the tieyser io-e per cent. Analyses of opal g from Frankfort by Stucke, h from Mo- f 1 ™’,* from (menilite), both by Klaproth; k from Cas- tella Monte by Beudant; wood opal (forming the substance of fossil wood) ^ from Oberkassel by E. Brandes; hydrophano m from Hubertsburg in Saxony by Klaproth:— 3 h * Jo I m Ollica .... 82-75 85-00 85-50 93'2 93’00 93‘13 Alumina, . 3-50 3-00 roo — 0 -i3 raa lied oxide of iron 3-00 1-75 0 60 (fig 03) 0 37 — Lime .... 0 . 2S _ 0 . 50 Q ./ __ _ Carbon ' ' ' ’ 1000 8 '°° n ' 0 ° 0,1 °' 13 1*00 (0'33 bituminous oil) —