256 METHODS OF GLASS MANUFACTURING. 



and sudden changes of temperature. When cooled 

 gradually, the particles arrange themselves in a regular 

 manner, or in a crystalline form. When cooled quickly 

 there is not time allowed for this regular formation and 

 the particles are forced to remain in that relative 

 position which they assume during the working, and 

 form an amorphous mass. Where the particles have 

 cooled most rapidly, this forced relative position is 

 greater while the. interior of the mass is not so subject to 

 it as the exterior and the later contracts in a greater 

 degree. The exterior layers are in a state of tension 

 compared with those of the interior and there exists a 

 lack of uniformity in the attraction of the particles for 

 each other. 



The customary form of the appliance in which the 

 annealing is done, is a brick lined oven, about 6 ft. high, 

 12 ft. wide by 10 to 12 ft. deep. After the temperature 

 of the oven has been raised to about 1,200° F., just be- 

 low a melting heat, the manufactured articles are piled 

 up in rows, as fast as they come from the blowers, 

 and when the oven is filled, the fires are banked, all 

 openings are closed and the contents allowed to cool. 

 The time required is from three to four days. A more 

 rapid and modern method is in the use of Leers, which 

 are built of brick and covered with a low arch. The 

 length may vary according to the amount of work to be 

 done, but they are usually constructed of such length and 

 width that the operation will be completed in from ten 

 to twenty-four hours. A not unusual size is width from 

 6 to 8 ft., and length 70 to 80 ft. 



At each side of the entrance the heat is applied, the 

 source being fuel oil, coke, coal or wood. Fuel oil gives 

 the best results as the heat is more uniform than can be 

 obtained from any other sources. The temperature em- 

 ployed is the same as is used in the ovens, about 1,200*^ 

 Fahr. The articles to be annealed are piled on iron 



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