CONTENTS. 



Page. 



Introduction _ - 7 



Location of smelter and appearance of surrounding vegetation 7 



Chemical principles underlying the investigation 8 



Experimental work 10 



Visible injury to vegetation by sulphur dioxid 10 



Compiled data , ** 



Experiments made in the Bureau of Chemistry . _ , ' 



Sulphur trioxid content of the foliage of fumigated and nonfuur r Vv e d, 



plants 



Compiled data '.".' 13 



Analyses made in the Bureau of Chemistry 14 



Sulphur trioxid content of the foliage of trees surrounding smelters . .. 14 



Analyses of foliage about the copper smelter near Redding, Cal - - - 14 



Analyses of foliage about a zinc smelter at Letmathe, Germany ... 17 



Comparison and discussion of results 19 



General conclusions . . 22 



ILLUSTRATIONS. 



PLATES. 



Page. 



PLATE I. View of the smelter in operation. 8 



II. Country about 1 mile west of smelter 8 



III. Fig. 1. View about 3 miles west of smelter. Fig. 2. View 



about 3| miles west of smelter 12 



IV. Fig. 1. Orchard about 2| miles southwest of smelter. Fig. 2. 



Country about 2 miles south of smelter 12 



V. View about 2 miles south of smelter 16 



VI. Country about 2| miles south of smelter 16 



TEXT FIGURE. 



FIG. 1 . Cabinet in which plants were fumigated 11 



5 



