Onihe Dfr'itn/icailon of Glass. 2G1 



time to stop to cnntemplatc small effects; they are obliged to 

 embrace too many Ihings ;it once. These remarks, curious 

 in themselves, remained without any consequence; and no" 

 one imasiined, or dared topublhh, that the civitallizalion of 

 glass and cenu-ntaliou, bv the process ot Reaunuir, were ab- 

 solutely one and the same. 



iSirJan>cs Hall, in his ingenious experiments on whin- 

 stone and lava*, discovered in these stones tile ])ropcrtv of 

 fusing into glass, and of returning to the state of stones, 

 according to circumstances. 



lie calls the latter. fact .'i devitrification; he saw that it 

 was the effect of a precipitation, and he explains it in a 

 true and satisfactory manner ; but being too mucii occupied 

 in deducing from this fact arguments in favour of the vol- 

 tauists, he neglected to follow in that plifPnoincnon whatever 

 interestino; it presented to the philosopher. Tfiis is the task 

 .which I have imposed upon mvself; and, in this memoir on 

 devitrification, I ])ropose to explain the result of my last re- 

 searches; as mv sitiuilion has placed at mv connnand u lire 

 exceedingly violent, and continued for several years, I was 

 enabled to observe what few have an opportunity of seeins;. 

 The facts which T am going to relate partly explain them- 

 selves; they are the result of the laws to which all bodies are 

 subject; the whole merit of the observation consists in 

 liaviug seen them insul)Stances in which, and at times when, 

 it was not known that these laws took place. 



The bottom of fum.ices for fusintr glass exhibit in gene- 

 ral large ciivilics, hollowed out bv the action of the fire and 

 of corroding substances, which oiten fuse crucibles. These 

 eavities become filled with a kind of glass called plcadih 

 This pieadil is the result of the ashes, which are vitrified, of 

 some of the stones of the furnace which are fused, and par- 

 ticularly of the glass which falls from the pots. Care is taken 

 to take it out at each fusion. At the end of the duration oi 

 tile furnace, the fo'-se, being enlarrred, cannot empty them- 

 selves entirely, and on that account fjimdilTvnvd'w.'s in them. 

 When the furnace is extinguished, the pieadil experiences a 

 cooling exceedingly slow, because it is surrounded by 

 mason-work, consisting of several cubic toises, which has 

 been heated for more than a year. I always observed that 

 it was in the glass ai the bottom of the furnaces that I 

 found crvstallizations; thev were diffused throughout the 

 inasa of the glass, which, in other rcspietb;, wasexccedimjly 



• liibliothequt BiUar.iii'iuc vol. xiv. Sec ;i!-0 rlic I'hilcsoplMC il Trans- 

 K 3 pure 



