Answer to Question 1
Natural gas is mostly methane and a little ethane, has a specific gravity 0.6,and a heat capacity around 1000 BTU/hr. Propane has a specific gravity of 1.5 and a heat capacity of 2500 BTU/hr
Answer to Question 2
The legend clearly identifies all symbol and letter designations used in the diagram, and the notes call attention to important facts relating to the circuit.