()<2 DEVITRJFICATION OF GLASS,* 



This Jail fa£t muft have prefented itfelf to every one, and will 



without difficulty be referred to theobfervations I (hall make. 



The more com- The firft remark which offers itfelf is, that the more com- 



pouaded cbe^fi pounded the nature of the glafs, the more eafily and readily it 



it lofes its vitre- will become devitrified : but in the fame manner as a folvent 



o;j„ uatwe. loaded with a great number of faline fubftances of different 



kinds, fuffers them to cryftallize more confufedly, fo likewife 



it is found that thefe glaffes do not prefent the mod regular cry- 



itallizalions. A precipitation takes place through the whole 



of the mafs; each of the component parts obeys the laws of 



affinities; at the fame time the tranfparency fpeedily difappears, 



and we no longer fee a piece of glafs, but a ftone. Through 



thisconfufed mafs it is neverthelefs impoffible not to obferve 



Battle elate. the rudiments of cryftals. Such is the manner in which bottle 



glafs comports itfelf in its devitrification. Thefe approach very 



much to the ftate of mere earthy glafles, having very little fait 



in their compofition. 



Experiment in Every one has an opportunity of keeping a common bottle 



tnc fma'l way. f black glafs in a fire long continued, and capable of foften- 



ingitspafie; it fpeedily changes colour, becomes grey, and 



affumes the appearance of ftone ware. In this manner we 



form the pottery of Reaumur, but without any procefs refem- 



bling cryftallization. 



ParticuLu e*a- But infiead of obferving the phenomenon in fo final! a mafs, 



miration of the jf we exam i ne the bottoms of the glafs furnaces in which thefe 



ch.inges in glafs , ° 



by flow cociag. bottles are fufed, we find that the glafs is ablolutely devitrified, 



and has a (Turned an appearance fo completely ftony, that the 

 moft experienced eye can fcarcely diftinguifh the bricks of the 

 furnace from the part which has been glafs. It is only by fol- 

 lowing the courf'e of the devitrification in pieces lefs advanced, 

 that we fucceed in diftinguifhing the glafs in a granulated flone, 

 which has rather the appearance of coarfe pottery, or a ftrongly 

 baked clay. 

 Ioftance-of the It often happens that the flow cooling of an hour or two i s 

 effca _ taking fufficient to produce the entire devitrification of bottle glafs. 



place in a ihort r . . = 



time. I have pieces of eight centimetres (2f inches) thick, which I 



obtained at the glafs works of Mr. Saget, of La Gare. One 

 of the pots was taken out of the furnace to be replaced; the 

 glafs remaining at the bottom of this pot was preferved from 

 cooling during the time the pot itfelf acquired the common 

 temperature, and by this means the nature of the glafs was 



entirely 



