of 25 to 105 thousandths of a percent the maximum dispersions of the nitrogen content were observed for grades ranging between 70 and 100 thousandths of a percent carbon and rose to nearly 35 ppm over the value indicated above under these conditions a not negligible number of pourings had to be rejected due to excessive nitridation consequently the twelve air permeable refractory elements were mounted in the bottom according to a geometry conforming to the essential characteristic of the invention that is along a circular ring in immediate proximity to the refractory side wall everything else being equal and for the same operating conditions as previously the tests which involved a much smaller number of charges were nevertheless sufficient to obtain significant statistical results these results showed that nitridation of the bath was kept constant at values of 20 ppm line 3 of the table with a reduced dispersion having entailed no rejection one encounters there results practically identical to those obtained without agitating gas blast 1st line of table and it can then be concluded that the invention renders the metal bath almost 34 transparent 34 to the agitating nitrogen a third series of tests was conducted following the method of introducing twelve air permeable elements as previously described with reference to the figures that is according to an arrangement in two categories 15 and 18 following an injection of gas according to an operational plan to be specified below the results showed a nitridation tendency which was limited to approximately 20 ppm line 4 of the table in spite of the activation of air permeable elements 18 in an intermediate arrangement in fact those results.