Page:The American Cyclopædia (1879) Volume VIII.djvu/19

 GLASS 11 compound, which solidifies on cooling into a transparent mass, without assuming a crystal- line structure. Such a substance is a product of the process of reducing metallic ores. The compounds produced by the glass manufactu- rer range from the most fusible combinations of one part of silica with two or three of soda or potash, which melt at a cherry-red heat and dis- solve in cold water, to the hard and refractory silicates of lime and alumina, some of which require the powerful heat of a furnace to soft- en them. Potash especially increases the fusi- bility of glass ; the oxides of lead and of zinc, and to some extent barytes, produce a similar eft'ect, while they also add to its softness, its lustre, its specific gravity, and its power of refracting light, and do not interfere with its perfect freedom from color, unless the lead be used in excess, when it gives a yellowish tinge. Iron, in the state of the silicate of the protoxide, imparts a dark green color; but on adding a small quantity of binoxide of man- ganese (Mn0 2 ) the color disappears, as the protoxide of iron is converted into the sesqui- oxide (Fe 2 O 3 ). and the manganese, losing one atom of oxygen, becomes MnO. Other me- tallic oxides, as those of uranium, copper, sil- ver, and gold, are also employed to give in- tense colors. Without reference, however, to substances used for imparting or removing colors, the essential materials of ordinary glass may be regarded as silica and boracic acid, the alkalies, lime, and oxide of lead. The varie- ties of glass are classified by Dr. Knapp as follows: 1. Bottle glass, including the varie- ties worked into hollow vessels and tubes, as common bottles, glass for medicinal bottles, white bottle glass for vials, tumblers, tubes, &c. The dark-colored varieties are distinguish- ed for their large proportion of oxide of iron and alumina, and none contain oxide of lead. The white bottle glass contains silica, soda or potash, and lime. 2. Window glass, inclu- ding English crown and cylinder or sheet glass; this is a silicate of potash or soda, lime, and alumina. 3. Plate glass, differing from the pre- ceding only by the greater purity and freedom from color of the materials. 4. Flint glass, used for grinding, &c., composed of silica, pot- ash, and oxide of lead. 5. Crystal, for optical purposes and table ware, consisting of silica or boracic acid, potash, and more lead than the preceding. 6. Strass, the paste used for imita- tions of precious stones; it contains much oxide of lead, and also metallic oxides used for the colors. 7. Enamel, composed of silica, soda, and oxide of lead, but rendered opaque by ox- ide of tin or antimony, which form a stannate or antimoniate with the soda. To these may be added the soluble glass, which is a sim- ple silicate of soda or of potash, or a mixture of the two silicates. The following analyses of several kinds of glass are from Knapp's " Chemical Technology : " VARIETIES OF GLASS. No. Analyit. Silica. Potash. Sod*. Lime. Mag- nesia. MnO. Alu- mina. Oxide of iron. Oxide of lead. Propor- tione.* 5:2 7:3 2:1 4:3 9:2 5:1 4:1 7:2 7:2 9:2 6:1 7:1 5: 6: 4: 5: 8: 6:1 6:1 9:2 4:1 7:2 7:8 6:1 Bottle glass, French 1 2 3 4 1 2 1 2 8 4 1 2 8 1 2 3 1 2 3 1 2 3 4 1 Berthier. .. Dumas Berthier '.'. Dumas. .. Richardson. Cowper. .. Berthier .. Dumas. .. Berthier .. Dumas. . . Berthier. . Faraday. . Dumas. . . Rowney. . 60-00 59-60 53-55 45-60 69-60 62-00 69-25 68-50 66-37 71-40 72-00 73-85 68-60 71-70 69-20 62-80 59-20 51-40 51-93 44-30 42-50 38 50 31-60 73-00 8-10 3-20 5-48 6-10 8-00 '5 : 50 6-90 12-70 15-80 22-10 9-00 9-40 13-67 11-75 11-70 7-90 8-30 11-50 '8 : 66 16-40 11-30 18-70 14-23 15-00 17-00 12-05 8-10 2-50 8-00 22-30 18-00 29-22 28-10 13-00 15-60 17-25 7-80 11-86 12-40 6-40 5-60 11-00 10-80 7-60 12-50 7-0 0-6 2-2 2-1 2 V 1-2 0-4 0-8 0-1 0-2 i-b 8-00 6-80 6-01 14-00 8-60 2-40 .2-20 10-00 8-16 0-60 2-60 8-50 1-20 0-40 1-20 i : 20 4-00 4-40 5-75 6-20 6 : 30 1-90 6 : 20 0-30 0-EO 2-60 0-40 0-80 l"-60 0-70 28-20 37-40 33-28 43-05 48-50 53-00 50-30 U 11 Medicinal glass French Window glass, French English Plate glass French " Venetian .. White glass, goblet, Bohemia French fusible tubing. Crystal, London optical " Newcastle Flint glass, Guinand ... " strass 0-50

2-0 1-80 1-00 Ox. tin. 9-80 " enamel Bohemian hard glass tubing 3-00 10-50 The later editions of Dr. Knapp's work give the following more recent analyses by Peligot : VARIETIES OF GLASS. 1 i 1 1 < 1 Oxide of tin. Oxide of lead. j i 1 1 J_ 3-5 Bohemian 76-015-08-0 80-917-60-7 67-7! 5-58-9 67-721-09-9 1-0 o-s i'-4 Bohemian opal glass. . . Venetian Aventurine. Bohemian mirror 7-1 2'3 1-1 3-9 The second of these is a remarkable glass, being a simple silicate of potash with 10 per cent, more silica than is contained in Fuchs's soluble glass. (See GLASS, SOLUBLE.) Particles of glass are dispersed through the semi-transparent, im- perfectly melted mass. The compound is not attacked by boiling water, and does not attract moisture from the air. The ingredients of amount of oxygen in the bases.
 * Relation between the oxygen of the acid and the total