possible that it combines with argon
From HUGHES AND GEDULD 225: "This contradicts the earlier statement that the Black Smoke contained 'an unknown element giving a group of four lines in the blue spectrum'. ... Actually, argon, as an inert gas, cannot combine with another element to form a compound."
GANGNES: The "blue spectrum" line is not in the serial. See Installment 6 note. HUGHES AND GEDULD (225) speculate that this kind of "carelessness in this final chapter probably reflects Wells's changing intentions regarding its publication." These "changing intentions" had much to do with Heinemann's insistence on the book being longer (HUGHES AND GEDULD 5-6).

