Calcium carbonate is also used in the purification of iron from iron ore in a blast furnace. The carbonate is calcined in situ to give calcium oxide, which forms a slag with various impurities present, and separates from the purified iron.
One re-hydrated package fills about 15-20 dishes. Mix 1 level teaspoon of dehydrated agar with 100 ml (3/8 cup) of water and then bring to a boil to make 100 ml of agar solution. Prepare Petri Dishes: Fill petri dishes to just cover the bottom. Typical 90-100mm dishes require 10-15 ml agar. Rotate the dish to obtain even surface coverage. Cover the dish immediately and let stand until firm. Store upside down in the refrigerator until ready to use.
A culture of mushroom mycelium growing on a petri dish of nutrient agar can take 24 hours (for morels) to upwards of a month (for Agaricus species and Stropharia Rugosa-annulata, for example) to spread across the better part of the plate.