VOL. XXVI.} PHILOSOPHICAL TRANSACTIONS. 503 



this manner, till none remains. Sometimes the metal leaves off sparkling, 

 when the coal is in part consumed, and covered with a bed of cinders, on which 

 the melted iron lies. For as the sparkling of the iron seems to proceed only 

 from the oily parts of the coal acting on those of the metal, the cinders hinder 

 this oil from passing from the coal to the iron, so that it remains quietly in 

 fusion. But if through any shake, or the like accident, the cinders be so 

 removed that the iron comes to touch immediately the coal, it begins to sparkle 

 afresh. 



I exposed to the focus, on a stone slate, iron and steel : they grew red-hot, 

 and melted without crackling or casting off any sparks ; they smoked very con- 

 siderably, and the melted metal changed gradually like an oil. After withdraw- 

 ing this melted matter out of the focus, it fixed in a regulus-like friable mass, 

 and appeared sometimes lightly striated, or shot into sharp points like needles. 

 Though this matter does not appear at all transparent, yet it may be considered 

 as the beginning of vitrification, or a middle state between metal and glass; for 

 it would vitrify in the end like other metals, if it could be held a sufficient time 

 in the focus without melting, or mixing with what sustains it ; but continuing 

 it long in the focus, the extreme heat of the sun necessary to keep it in perfect 

 fusion, melts also the stone or cupel that contains it, the result of which mix- 

 ture is a brown or greyish sort of enamel. 



We may then consider this regulus mass as a half vitrified iron, as it is de- 

 prived of great part of its sulphur. If one adds to this mass a sulphur like 

 that which was taken from it, from being friable it becomes very hard and mal- 

 leable, and its former dulness changes to the brightness of a metal. This is 

 what I have experienced in exposing again this matter to the focus upon char- 

 coal ; it melts, and so continues a considerable time in fusion without sparkling ; 

 but at last it sparkles with the same briskness as iron itself, and when withdrawn 

 from the focus, appears nothing different from melted iron. 



From these experiments it appears, that iron contains a sulphur or oily sub- 

 stance, that renders it bright, malleable, and easy to melt. That this sulphur 

 is raised by the fire of the sun, when the metal is for some time held in fusion 

 in the focus of the glass. That this sulphur may be raised by the flame of 

 common fire, which though not strong enough to melt the iron, yet is able to 

 reduce it to an eschar or sort of rust. That iron deprived of this sulphureous 

 part, melts into a regulus, or brittle and friable mass, in colour much like an- 

 timony. That if one can hold a sufficient quantity of this matter long enough 

 in the focus by itself, without melting or mixing with the body that contains it, 

 it perfectly vitrifies. That this glass or metallic regulus, with the help of a 

 little oil, returns to its former state of a metal. That it reassumea thia metallic 



