54 A^^T O^ GLASSMAKINCI, 



S. Tae results of the annealing of large loajses in cvucl- 

 ble-iiiouUb : 



3. The colour'nu; of glass red by copper, and in cements : 



4. The alteration glass undergoes by long-continued heat: 

 5- This alieration by the tire of our farnaces compared 



^vith that of volcanoes; : 



6". Lastly, what constitutes the real difl'erence between 

 transparent and devitrilied glass. 



Obs. I. Separation of ^hss of different densities by eliquatioiu 



FxiiKirimeiits la 177t) I accompanied Mr, de Buffon to the plate glass 

 t>i Bjnoq. niauufactoiy then existing' at Kouclle, near Langres, under 

 the direction of Mr. Allut, who wrote the article g-/ac<?n> in 

 the Enajclopcdie. His object was to make some experiments 

 on the fabrication of a mass of flint-glass, for constructing' 

 the ientille a echelons described in the first volume of his 

 Supplements. I shall not speak of the various processes 

 tried, and the difficulties that obliged him to give up the 

 hope of obtaining one siMgle piece of sufiicient thickness ; 

 but confine myself to the very extraordinary result of one 

 trial 1 witnessed, and which I conceive may be compared to 

 what metallurgists term eli(juation. 

 Glass sfp^- A mat-s of flint-glass*, 37 «nil. [1*46 inches] thick, had 



small "rata^T^J"^^ '^^^'^ *""" *^"^ ^" the copjSer table. A portion of this 

 if by eliqua- ghiss, about three or four fingers thick, was left in the cru- 

 *•'""■ cible ; and it was supposed, that, by charging it afresh with 



■ the common composition, the glass obtained would be so 

 much vhe liner, because it would approach nearer in qua- 

 lity to flint-glass. The refined glass having been ladled into 

 the cistern, and run on the table to the thickness of three 

 lines, was placed in the annealing furnace. When it was 

 taken out, its qviality was examined ; and, to our great 

 surprise, on cutting it there appeared, instead of a single 

 glass, two very distinct strata, the line of separation of 

 which was pliiinjy ^larked, luid extended throughout the 

 ii<ass ; the lower stratum occupying about one third of the 



♦ The compoeitioi) wa? ;}2 parts powdered Madagascar crystal, 

 as minium, id soda., and j nitre, Elfim, dc Chim. de Dijon, vel, I, 

 ?■ 179- 



thickness. 



