Task: Pos Tagging
Input (English): Sentence: Following {{ observation }} of the fact that the reaction rates of supposedly identical reaction mixtures prepared on the same filling manifold and exposed under identical conditions often differed by several hundred per cent , a systematic series of experiments was undertaken to see whether the difficulty could be ascribed to the method of preparing the chlorine , to the effects of oxygen or moisture or to the effect of surface to volume ratio in the reaction tubes . 
Word: observation
Output (English): NOUN