Gas reaction apparatus and multi-wall pipe type burner therefor

In a gas reaction apparatus in which apparatus at least one gaseous raw material of optical fiber and at least one kind of gas different from said gaseous raw material and from a mixture including said gaseous raw material, which gas includes combustion gas, are introduced into a reaction vessel from at least one multi-wall pipe type burner which burner has a plurality of gas passages whereby said gaseous raw material is subjected to flame hydrolysis into powdery glass which powdery glass is deposited on a rod member whereby said powdery glass is formed into porous base material of optical fiber, the improvement comprising:

• a means for heating or heat insulating at least one of said gas passages for said gaseous raw material or said mixture at a temperature so that a saturated vapor pressure of whole kinds of said gaseous raw material is set higher than a partial pressure of raw material of optical fiber in said gaseous raw material or said mixture when said gaseous raw material or said mixture is fed through said heated or heat insulated gas passages.