I’ve written about the CAS Registry – the enormous database of small and large molecules – on several occasions over my quarter of a century in science communication. It usually comes up when they reach a milestone. Indeed, I remember writing about the day they registered their 10 millionth structure, that was either in The Guardian or New Scientist, don’t remember, it was the early 1990s. I wrote about it much more recently here on the Sciencebase blog back in September 2009 when they reached 50 million structures. How can there be so many chemicals, surely we are approaching some kind of limit? Well, no. We are nowhere near