the conventional natural gas it is concluded that the natural gas additive according to the seventh preferred embodiment of the invention can save about 58 1 fuel in comparison with the conventional natural gas for verifying the preheat piercing effect of the invention the following test is conducted workpiece to be pierced is 40 mm steel plate preheat piercing methods to be performed are propane oxygen flame method acetylene oxygen flame method the natural gas additive of the second preferred embodiment of the invention oxygen flame method and the natural gas additive of the seventh preferred embodiment of the invention oxygen flame method test results are shown in fig8 the above test is conducted under the same weight flow rate with respect to different gases it is concluded that time for piercing of each of the natural gas additive of the second preferred embodiment of the invention oxygen flame method and the natural gas additive of the seventh preferred embodiment of the invention oxygen flame method is much less than that of each conventional method thus the invention has an advantageous effect for verifying the flame temperature increase effect of the invention the following test is conducted flame temperature measurement is chur baum ferry sodium line reversal method flame types to be tested are pure natural gas oxygen flame propane oxygen flame acetylene oxygen flame the natural gas additive of the second preferred embodiment of the invention oxygen flame and the natural gas additive of the seventh preferred embodiment of the invention oxygen flame test results are shown in fig9 it is concluded that flame temperature increase of each of the natural gas additive of the second preferred embodiment of the invention oxygen flame and the natural gas additive of the seventh preferred.