Brownlee's Stack Loss Data
[1] case
[2] 10 times % of the ingoing ammonia
[3] rate of operation of the plant
[4] temperature of cooling water 
[5] concentration of acid circulating 

The data were obtained from 21 days of operation of a plant for the
oxidation of ammonia to nitric acid. The nitric acids which are produced
are absorbed in a countercurrent absorption tower. The dependent variable
is 10 times the percentage of the ingoing ammonia that ascapes form 
the absorption tower; the more that escaspes, the less efficient the plant.
X1 is the rate of operation of the plant; X2 is the temperature of cooling 
water which is circulated through coils in the absorption tower; X3(rescaled)
is the concentration of acid circulating.