A data set from Oehlert (2000) \emph{A First Course in Design and
Analysis of Experiments}, New York: W. H. Freeman.

Data originally from Xhonga, R. (1971).  ``Direct gold alloys---part {II}.''
{\em Journal of the American Academy of Gold Foil Operators\/}
{\em 14}, 5--15.

Columns are alloy, method, dentist, and hardness (diamond pyramid
hardness number).