42 Effect of Zinc Compounds 



soils for different poisons varies, that basic salts are absorbed, while the 

 acid salts may pass completely through the soil in the drainage water. 



Freytag (1868) stated that zinc is retained by the soil in the form 

 of oxide, which is derived from dilute zinc compounds as they filter 

 through the soil, by decomposition by the salts of the soil. For field 

 earth the limit of absorption of zinc oxide from zinc sulphate is between 

 •21 %— -24 7„ of the earth. 



F. C. Phillips (1882) corroborated Freytag's statement as to the 

 absorption of small quantities of zinc by the roots of plants, but he 

 states as a fact that both lead and zinc may enter plant tissues without 

 causing any disturbance in the growth, nutrition or functions of the 

 plants, a conclusion that is obviously incorrect or at least incomplete in 

 view of later work on the subject. His choice of plants was certainly 

 unusual, including geraniums, coleas, ageratums and pansies, the poison 

 used being zinc carbonate. 



Holdefleiss (1883) stated that in spite of a soil content of 2 °/^ zinc 

 the vegetation was not in any way harmed, clover fields and meadow 

 lands on zinc soil presenting a normal appearance. This observation 

 was quite inconclusive, as the author proceeds to say that of the plants 

 that were able to absorb zinc salts without disadvantage the most 

 luxuriant were the so-called zinc plants — the exceptions that prove the 

 rule. Two years later Baumann showed that such insoluble zinc salts 

 as the carbonate and sulphide in the soil cannot hurt plants. These 

 salts are certainly dissolved to some extent by water containing COj 

 but solution is hindered by the constitution of the soil. He also found 

 that the various kinds of soil act differently upon zinc solutions, the 

 absorptive power of pure humus soils (" reinem Humusboden ") for zinc 

 solutions being the strongest. Clay and chalk soils also decompose 

 such solutions energetically, while poor sandy soils have only a weak 

 power of absorption. This selectivity of absorption may account 

 for the difference in the toxicity of zinc salts to plants in the various 

 soils. 



Storp (1883) experimented to determine the changes in the various 

 characters of the soil by the action of zinc salts on it, and he makes the 

 remarkable statement that in some soils the presence of zinc generates 

 free sulphuric acid, which is particularly injurious to plant life. Grasses, 

 young oaks and figs showed a decrease in dry weight, nitrogen and fat, 

 as the quantity of zinc compounds increased in the water added to the 

 soil. Both the quality and the quantity of the crop were adversely 

 affected. This decrease in the dry weight due to the presence of zinc 



