Iron comes from Iron Ore via the Forge. Iron Ore can be found in Iron Nodes in the Stalactite layer and Lava layer. The ore has to be harvested with an Extractor, as the node itself cannot be pulled with Power Cells, it also cannot be placed. All Ores can be smelted into bars in a Forge for further processing.
It depends on the substance (water for example has 1000 grams to a liter, other substances have more grams or less grams to a liter depending on a property (called the density measured in grams / liter) of the substance.
You can now convert between liters (or litres, with British spelling) and metric tons using the liters to metric tons converter. This assumes that you know the density of the liquid you wish to convert. You can also convert between various volumes and weights using the weight to volume converter. If you don't know the exact density of the liquid in question, you can use the drop-down list of liquids.