5g DEVITRIFICATION OF GLASS. 



the metal, every affignable point of the galvanic plate is effi- 

 cient at the fame time, therefore the intenfity will be as the. 

 furiace, and the powers as the fquares of the intenfities. 

 I am, Dear Sir, 



Your's, refpect fully, 



C. WILKINSON. 

 No, 1 9, Soho Square. 



Gbfs is not a 



XIV. 



On the Devitrification of Glafs and the Phenomena which hap' 

 pen during its Crj/ftallization. By Dartigues.* 



OOME philofophers have confidered glafs as a chryfialliza- 

 cryftaJlization. tion ; and this opinion appears natural on confidering the tranf- 

 parence of glafs or of cryftal, from the latter of which the 

 term for defignating the regular and fpontaneous arrangement 

 of the particles of bodies has been taken. But on clofer re- 

 flexion, this notion is found to be erroneous. In fact glafs" 

 never affecls a cryftalline figure, either in its furface or its frac- 

 ture j it never prefents chryftals of its own proper fubftance, 

 fuch as are feen in metals flowly congealed; and whenever 

 cryftals are formed in the mafs of glafs, they are foreign to 

 the part which ftill continues vitrified; they may be confidered 

 as a ftep the reverfe from that of vitrification, as I fhall 0iow 

 in the courfe of the prefent paper. 

 Vitreous fufion On the firft explanation of vitreous fufion, I muft diftinguifh 



diftina from an( ] f e p ara te it from the fufion of certain other bodies which 



that of falts. r 



flow without addition in the heat of our furnaces, fuch as bo- 

 rax, the phofphoric acid and others. In thefe bodies the con- 



* Tranflated from the Journal de Phyfique, LIX. 5. 



The author of this memoir, who is proprietor of the glafs-works 

 and other eftablifhments of Voneche (Sambre-et Meufe) has under- 

 taken to draw up for the French National Inftitute a treatife on the 

 art of glafs-making, to ferve as a continuation to the arts and trades 

 of the Academy. The firft part is in readinefs to appear, many of 

 the plates being ready. The fecond part relates to the ufes of glafs 

 in the arts. And the third part confifts of detached memoirs upon 

 the phyfical and chemical properties of glafs. The prefent differta- 

 tion is extra&ed from one of thofe memoirs. — J. C. Delametherie. 



denied 



