def pollutant():
    """
    Water treatment example from BHH2, Ch 5, Question 19.

    Description
    -----------
    The data are from the first 8 rows of the pollutant water treatment example
    n the book by Box, Hunter and Hunter, 2nd edition, Chapter 5, Question 19.

    The 3 factors (C, T, and S) are in coded units where:
    C = -1 is chemical brand A; C = +1 is chemical brand B
    T = -1 is 72F for treatment temperature; T = +1 is 100F for the temperature
    S = -1 is No stirring; S = +1 is with fast stirring

    The outcome variable is:
    y = the pollutant amount in the discharge [lb/day].

    The aim is to find treatment conditions that MINIMIZE the amount of pollutant
    discharged each day, where the limit is 10 lb/day.

    Dimensions
    ----------
    A data frame containing 8 observations of 4 variables (C, S, T and y).

    Source
    ------
    Box, G. E. P. and Hunter, J. S. and Hunter, W. G.r, Statistics for
    Experimenters, Wiley, 2nd edition, Chapter 5, Question 19, page 232.

    Example
    -------

    """
