162 MANUFACTURE OF GLASS. 



feet fusion ; and dining this process any scum which arises must be 

 removed by ladles. NVhen the glass is perfectly melted, the glass 

 blowers commence their operations. 



The following compositions of the ingredients for glass are ex. 

 tracted from the Handmaid to the Arts : 



" For the best Hint-glass, 120lbs. of white sand, oOlbs. of red 

 lead, 40ll>s. of the best pearl. ashes, 20lbs. of nitre, and five ounces 

 of magnesia ; if a pound or two of arsenic be added, the composi- 

 tion uili fuse much quicker, and with a lower temperature. 



" For a cheaper flint-glass, 120lbs. of white sand, 35lbs. of 

 pearl-ashes, 40lbs. of red-lead, 13lbs. of nitre, six pounds of arsenic, 

 and four ounces of magnesia. 



" This requires a long heating to make clear glass ; and the 

 heat should be brought on gradually, or the arsenic is in danger 

 of subliming be-fore the fusion commences. A still cheaper compo- 

 sition is made by omi ting the arsenic in the foregoing, and sub- 

 stituting common sea. salt. 



" For the best German crystal glass, 120lbs. of calcined flints 

 or white sand, the best pearl-ashes 70lbs., saltpetre lOlbs., arsenic 

 half a pound, and five ounces of magnesia. Or, a cheaper com. 

 position for the same purpose is, 1201bs. of sand or flints, 46'lbs. of 

 pearl-ashes, seven pounds of nitre, six pounds of arsenic, and five 

 ounces of magnesia. This will require a long continuance in the 

 furnace ; as do all others where much of the arsenic is employed. 



" For looking-glass plates, washed white sand, GOlbs., purified 

 pearl-ashes 25lbs., nitre I5lbs., and seven pounds of borax. If 

 properly managed, this glass will be colourless. But if it should 

 be tinged by accident, a trifling quantity of arsenic, and an equal 

 quantity of magnesia, will correct it; an ounce of each may be 

 tried first, and tte quantity increased if necessary. 



*' The ingredients for the best crown-glass must be prepared in 

 the same manner as for looking-glasses, and mixed in the following 

 proportions : 6oibs. of white sand, 301bs. of pearl-ashes, and 

 15lbs. of nitre, borax a pound, and half a pound of arsenic. 



** The composition for common green window glass is 120lbs. of 

 white sand, SOlbs. of unpurified pearl-ashes, wood-ashes well 

 burnt and sifted, GOlbs., common salt 20lbs., and five pounds of 

 arsenic. 



" Common green bottle-glass is made from 200lbs. of wood- 

 ashes, and JOOlbs. of sand; or IfOlbs. of ashes, lOOlbs. of saud, 



