An article in the Textile Research Institute Journal (1984, Vol. 54, pp. 171€“179) reported the results of an experiment that studied the effects of treating fabric with selected inorganic salts on the flammability of the material. Two application levels of each salt were used, and a vertical burn test was used on each sample. (This finds the temperature at which each sample ignites.) The burn test data follow.

(a) Test for differences between salts, application levels, and interactions. Use α = 0.01.

(b) Draw a graph of the interaction between salt and application level. What conclusions can you draw from this graph?

(c) Analyze the residuals from this experiment.

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Salt Level Untreated MgCl, NaCl CaCO, CaCl, Na,CO, 751 812 752 739 733 725 827 728 731 728 727 761 876 764 726 720 719 755 945 794 741 786 756 910 881 760 744 771 781 854 919 757 727 779 814 848 2.