358 



USE OF SULPHATE OF SODA IN GLASSMAKING. 



General obser 

 vations. 



Advantages. 



Requires con- 

 siderable care. 



different substances that may be employed in glass-houses, 

 I conceive, that the following particulars will not be un- 

 interesting. They who wish for information more at largC 

 may find it in the work which Dr. Gehlen has lately pub- 

 lished, entitled Beytrage zur wissenschaftUchen Begruerim 

 dung der Glasmacherkunst, Attempt to establish the Art 

 of Glassmaking on Scientific Principles, Munich, 1810. 



From a number of experiments, made in the large way 

 by Mr, Francis Baader and Dr. Gehlen, it appears ; 



1, That sulphate of soda perfectly freed from its water 

 of crystallization, may be very successfully employed in 

 manufacturing fine white glass, without the addition of pot- 

 ash or soda. 



2, That in using this flux there is a considerable gain in 

 point of time; and consequently in the product of a given 

 furnace, and in materials. These advantages arise from a 

 larger quantity of silex being dissolved by sulphate of soda 

 freed from its water of crystallization. 



3, That it only requires great accuracy in the addition of 

 the quantity of charcoal necessary to effect the decompo- 

 sition of the sulphate of soda. This is so essential, that 

 sometimes a single hundredth part too much, or too little, 

 almost spoils the vitrification, or colours the glass. It 

 must be observed too, that it is difficult to give precise di- 

 rections for the quantity of charcoal to be employed, be- 

 cause the proportion must vary according to its dryness or 

 moisture. If it be moist, it will yield more carbonic acid, 

 ■which cannot certainly be advantageous to the vitrification. 



4, That sulphate of soda cannot be employed so well in 

 substance in the melting pots ; but that it is better first to 

 make a sulphuret of soda, in order to get rid of the large 

 quantity of carbonic acid, which is formed in the disoxi- 

 dation of the sulphuric acid, and would cause too great an 

 effervescence in the melted matter. 



5, That the glass-gall is decomposed by an addition of 

 charcoal in all the other manufactures of glass, which is a 

 great advantage, because this gall is the greatest enemy to 

 the manufacture of fine glass. 



6 That the pots, in whith the glass is melted by means 

 tiontothepots.^j sulphate of soda, must be made with much care, and 



with 



Should be first 

 decomposed 

 into a sulphu- 

 ret. 



Glass-gall. 



Peculiar atten- 



