The blacksmith uses small coals because the small pieces thereof are more easily ignited than large lumps would be, and they convey heat better by completely surrounding the articles put into the fire. He sprinkles water on the coal dust to hold its particles together by cohesion, until the heat forms it into a cake. A strong blast of hot hair drives the vapour of the water away, and leaves a porous mass to the action of the fire.
309. Why, when the blacksmith thrusts a heated iron into a tankard of water, do we recognise a peculiar smell?
Because the intense heat disengages a small volume of the gases of which water is formed.
"Oh the depth of the riches both of the wisdom and knowledge of God! how unsearchable are his judgments, and his ways past finding out."—Rom. xi.
310. Which gas do we (in this instance) recognise by the smell?
The hydrogen gas. Oxygen gas possesses no odour.