OK. I do have a B.S. degree in chemistry and do have a job title called ‘scientist’ now, but college is more than ten years ago and I am not in the profession of chemistry. Consider yourself warned.
If checked under microscope, the crystal structure of sugar is distinctive (even to average minds like me), it is the fastest way to see if there is anything other than sugar (C6H12O6) in the mixture. The molecular formula C17H23NO3 could be acetoxyketobemidone, atropine, mesembrine, or hyoscyamine, which consist exactly the same group of molecules of C, H, N, O, but with different structures. Sherlock mentioned narcotics, so I think he had acetoxyketobemidone, a type of opioid, in mind. Then he tested if there is anything insoluble to water. Sugar is readily soluble, but narcotics are probably not. Finally, sulfuric acid (H2SO4) dehydrates the H2O’s in sugar so the slide turned brown, sulfuric acid may have reactions with C17H23NO3 too. I truly don’t know what’s going on with deuterium here.
This is the reason I love her so much: I totally don’t understand what she said, but feel the sexiness in every word of hers.