There's been consolidation in the air products sector ever since Airgas was bought by Air Liquide (AIQUY) , said TheStreet's Jim Cramer. Now there's the merger of Praxair (PX) and Linde (LNAGF) . "I think that is a very fractured industry that has always been moms and pops being bought. Looks like that industry is finally going to be an oligopoly," Cramer said. He advised investors to "buy air products" stocks.