TOMATO LEAF MOLD 



23 



Reaction with Paint 



Various paint pigments^ were added to water and painted on panes of glass. 

 After drying, these pigments were exposed in a large chamber to burning sulfur 

 fumigation and 5 percent suspensions of the residues in distilled water were made. 

 The filtrates were tested for pH values and then sprayed on delphinium and 

 tomato plants for toxicity manifestations. The results were recorded three to 

 five days after spraying (Table 12). Injury of varying degree occurred. The 

 greatest injury resulted from zinc oxide and leaded zinc. Basic lead carbonate 

 and aluminum powder did not cause injury. No definite correlation was shown 

 between the pH value of the extract and its toxicity to plant foliage. Some of the 

 pigments showed a marked hydrolysis after fumigation, expressed in the strongly 

 acid character of the filtrates, i. e. titanium dioxide, Titanox B, Lithopone, and 

 zinc sulfide; and extracts of these pigments caused some injury in one or another 

 of the experiments. Extracts of pigments not exposed to burning sulfur fumiga- 

 tion were not toxic. 



Table 12. — Effect of Exposure of Paint Pigments on Glass Panes to 



Fumigation with Burning Sulfur, and the Action of Extracts 



OF THE Residue on Plant Foliage 



Paint Pigment 



pH of Paint Pigment 



Degree of Injury 

 from Extract 



Before SO. After SO, Delphinium 

 Fumigation Fumigation 



Basic Lead Carbonate 6.6-6.8 6.4-6.6 None 



Lead Sulfate 6.2-6.4 6.3-6.4 Slight 



Titanium Dioxide 6 . 6-6 .8 3 . or less Slight 



Titanox B 6.8-7.0 3 . or less None 



(Titanium Dioxide. . . .25%) 



(Barium Sulfate 75%) 



Zinc Oxide 6 . 6-6 .8 6 . 4 6 . 6 Severe 



Leaded Zinc 6 . 6-6 .8 6 . 4-6 . 6 Severe 



(Zinc Oxide 65%) 



(Lead Sulfate 35%) 



ZincSulfide 7.0-7.2 4.4-4.6 None 



Lithopone 7.0-7.2 4.3-4.5 None 



(ZincSulfide 28%) 



(Barium Sulfate 72%) 



Aluminum Powder 4.6 None 



None 

 Slight 

 None 

 None 



Severe 

 Severe 



Slight 

 Slight 



None 



These same white pigments were moistened in Petri dishes and exposed to an 

 atmosphere of burning sulfur. They were then dried and washed and the amount 

 of water-soluble material in each determined (Table 13). Basic lead carbonate, 

 which did not cause injury in any of the experiments, showed the least water- 

 soluble material. Zinc oxide and leaded zinc, which caused the greatest injury, 

 also yielded the most water-soluble material. In other instances injury, if any, 

 was slight and the amount of water-soluble material was likewise small in pro- 

 portion. The zinc oxide pigments Nos. 2 and 412 were rendered appreciably 

 soluble. 



'Paint pigments supplied through the courtesy of Sherwin-Williams Company, Cleveland, Ohio. 



