Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Water gas is a synthesis gas, containing carbon monoxide and hydrogen. It is a useful product but requires careful handling because of the risk of carbon monoxide poisoning. The gas is made by passing steam over red-hot coke: C + H2O CO + H2. The reaction is endothermic so the coke must be continually re-heated to keep the reaction going. This was usually done by alternating the steam stream with an air stream.