This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
The chalk trays fitted at the lower edge of blackboards soon collect considerable chalk dust and the chalk sticks dropped into it are, therefore, disagreeable to handle. A simple way of keeping the sticks clean is to cover the trays with wire mesh which is shaped like a tray but not so deep as the chalk tray. Thus the chalk dust will fall through this screen and be out of the way of the sticks.