MANUFACTURE OF GLASS. ^35 



boiled together in five pints of water, for the space 

 of a few minutes. 



MANUFACTURE OF GLASS. 



This beautiful material is not of modern inven- 

 tion ; it was known to the ancient Romans, but it 

 was by no means common among them, and they 

 do not appear to have had the method of forming 

 it into vessels of various shapes as is practised at 

 present. 



Glass is made by fusing together silex and 

 potash^ or soda, in proper proportions. Sea sand^ 

 which consists almost entirely of quartz arid flints 

 reduced to powder, is generally used for this pur- 

 pose. The alcali is generally procured from the 

 burning of sea weeds ; these are cut, dried, and 

 burned in pits dug in the ground ; after a sufficient 

 quantity of them have burned in the same pit, a 

 melted or liquid mass is found in the bottom, 

 which, after being well stirred, is suffered to cool ; 

 it is then called kelp, and consists of a mixture of 

 soda, potash, and parts of half burnt v/eeds, toge- 

 ther with shells, sand, and other impurities. 



When the ingredients of which glass is composed 

 are perfectly fused, and have acquired a certain 

 degree of heat, which is known by the fluidity of 

 the mass, part of the melted matter is taken out at 

 the end of a long hollov/ tube, which is dipped 

 into it, and turned about, till a sufficient quantity 

 is taken up ; the workmen then rolls it gently 

 upon a piece of iron, to unite it more intimately. 

 He then blows through the tube, till the melted 

 mass at the extremity swells into a bubble, after 



