USE OF SULPHATE OF SODA IN GLASSMAKING.* 359 



■with a different proportion of materials, because this glass 

 attacks them much more than that made with potash. 



7, That sulphate of soda may be very well prepared by Preparation of 

 decomposing muriate of soda ; and for this purpose the sulphate. 

 waste of vitriol manufactories may be employed, which is a 

 considerable saving. 



8, Lastly, it is well known, that, when fine glass is Blebs in glass. 

 made, and more soda or potash is mixed in it than in com. 



mon glass, the glass, if not properly cooled before it is 

 wrought, though at first very pure, begins soon to enter 

 into fermentation while working, and afterward appears 

 full of blebs. It is observable, that glass made with feld- 

 spar containing potash always abounds in blebs ; yet it is 

 possible, to make good glass of it, and thus turn to ac- 

 count the potash contained in it. 



Experiments. 

 As the sentiments of Kreschmann, Pott, Laxmann, Gren, Experiments, 

 Lampadius, Van Mons, and Pajot-Descharmes, respect- 

 ing the use of sulphate and muriate of soda in the fabrica- 

 tion of glass, differ widely, it was necessary to make the 

 following experiments, to ascertain the processes, that might 

 answer. ^ 



1. First a mixture of quartz and sulphate of soda, in Experiment l. 

 the proportions of 100 to 60, was made, and exposed to the 



fire of a glass-house furnace twenty-two hours. At the 

 end of this time no virtification had taken place, or 

 at least it was imperfect, however high the heat was car- 

 ried. 



2. Quartz, sulphate of soda, and burnt lime, were taken Experiments. 

 in the proportions of 100, 100, and 15, and heated. A 



second mixture was made in the proportions of 100, 50^ 

 and 20; and a third in the proportions of 100, 54, and 17. 

 The third mixture was heated in a furnace the fire of 

 which was urged by bellows. At the expiration of four 

 hours more vitrification had taken place, it is true, than in 

 the first experiment; but the glass was very stiff, and as it 

 were stony. 



3. Quartz, calcined potash, lime, and sulphate of soda, Experiment 3. 

 were mixed in the proportions of 100, 10, 17, and 43, and 



at 



