A general procedure of how to perform a loss on ignition is as follows:
# Weigh the empty crucible that the sample is to be placed in and record its weight in a lab book.
# Place the sample in the empty crucible and weigh the crucible again with the sample in it. The new weight minus the empty crucible weight is the sample's wet weight.
# Place the sample in the drying oven or blast furnace as required. 
# Set the oven or furnace to the desired temperature. If the researcher wants to find the dry weight of the soil then the furnace would need to be 100 °C.
# Leave the sample in the furnace for the desired length of time. If the researcher wanted to know the sample's dry weight and is using a furnace set at 100 °C, then the researcher would usually leave the furnace on overnight.
# Open the oven but also back away from it at the same time since the hot air escaping from the furnace can burn bare skin.
# Allow the oven and sample to cool down before removing the sample from the oven.
# Weigh the crucible with the sample again. Subtract the empty crucible weight from this new weight and that is the sample's dry weight.