A chemist wishes to test the effect of four chemical agents on the strength of a particular type of cloth. Because there might be variability from one bolt to another, the chemist decides to use a randomized block design, with the bolts of cloth considered as blocks. She selects five bolts and applies all four chemicals in random order to each bolt. The resulting tensile strengths follow. Analyze the data from this experiment (use α = 0.05) and draw appropriate conclusions.

Bolt
Chemical 1 2 3 4 5
1 73 68 73 71 67
2 73 67 75 72 70
3 75 68 78 73 68
4 73 71 75 75 69