282 EARTHS. 



and might therefore be used for clock pendulums ; it is a bad con- 

 ductor of heat, and a large mass of it poured in fusion into water, will 

 remain red hot in the inside, for several hours after the outside is solid. 



3. MECHANICAL OPERATIONS. It would exceed the limits of a 

 work like this, to describe even the outlines, of the ingenious opera- 

 tions by which glass is fabricated into the various forms in which we 

 see it. In general, it is blown by the breath of the artist, injected 

 through an iron tube, to which the melted glass is made to adhere, 

 by dipping and rolling one of its ends, repeatedly in the crucible ; 

 and in the early part of the operation, while it is inflated, it is rolled 

 on a smooth iron plate. I will briefly describe a few cases, most of 

 which I have seen, and they will serve as examples for the rest. A 

 porter bottle is partly blown, and then allowed to drop into a mould 

 of copper, brass, or iron, in which, by a vigorous inflation, it receives 

 its form ; the bottom is indented to make it stand ; the mould opens 

 with a hinge, and another workman attaches a rod, having a little 

 melted glass upon it to the bottom of the bottle ; the neck is cracked 

 off by touching it with an instrument wet with cold water, and the 

 broken mouth, being again heated, is shaped by introducing a revolv- 

 ing iron into it, and a coil of melted glass is wound around to give 

 it strengh ; it is then carried away to the annealing furnace, to be 

 gradually cooled. Glasses consisting of several parts, are blown sep- 

 arately, opened, moulded, shaped and stuck together while hot ; the 

 foot of a wine glass is blown, as well as the conical part. 



A glass tube is drawn, by blowing a little into a mass of melted 

 glass on the end of the iron tube, and then an assistant pulls the mass 

 with iron pincers, and moves off rapidly or slowly, as the tube is to 

 be coarser or finer. 



Plate glass is cast on an iron table ;* an iron cylinder of five 

 hundred pounds weight or more, is passed over it to spread it 

 smoothly, and it is finished by being ground and polished. Plates 

 have been made of twelve feet by six. The smaller glass plates are 

 blown, opened by a chisel and mallet, and cut, while hot, by shears, 

 spread open upon a table, and afterwards annealed and cut by the 

 diamond. Plates can be made in this way, of four or five feet, by 

 two or three. Window glass is blown, and either cut open and 

 spread ; or in the best kinds, after being blown into a huge globe, 

 this is fixed at the bottom, to another iron tube, or rather an iron 

 rod ; the neck is cracked off, and the mouth is heated at a flaming 

 furnace, while the bottle is made to revolve rapidly, and by the cen- 

 trifugal force, the mouth opens and widens, and the globe suddenly 

 expands into a wheel, forty eight or fifty inches in diameter, called 

 by the workmen, a table ; this operation is called flashing, and is 



* Copper tables and rollers were formerly employed, but the copper is apt to 

 crack. 



