Sentence:  To reduce heat transfer from the hot <WSD>gas</WSD> to this anode holder outside the region of the arc , a carbon shield was attached to the surface providing an air gap of 1/16 inch between the plate and the surface of the anode holder . 
Meaning of the word marked with <WSD> tags:  a fluid in the gaseous state having neither independent shape nor volume and being able to expand indefinitely