Again, the relative rotatory effects of the NO, and methyl groups may be ascertained from another series of compnrisons, namely, dinitro-0.3475 gave 0,1666 K,S04. KHC4H406 requires K = 20.74 per cent, I n order t o ascertain whether racemisation had occurred in the preparation, this potassium hydrogen tartrate was examined polarimetrically in aqueous solution a t 20' : glacial acetic acid. K = 21.50. * Miss Hal tlc subsequently obtaineda mcalting point of 113'6' by crystallising from N 2