Effect of Copper Compounds 23 



all the solids. Lupin roots proved unable to withstand an exposure of 

 24 hours to a concentration of copper sulphate of 1 molecular weight 

 in 60,000 litres of water (i.e. about 1 part by weight CuS0 4 . 5H 2 O in 

 240'4 parts water), but the addition of solids caused a great decrease 

 in toxicity. When the amount of copper was diminished an advantage 

 was regularly obtained in favour of the cultures containing the solid 

 bodies. On the whole the ameliorating action of solids is more clearly 

 marked with dilute solutions of strong poisons than with relatively 

 concentrated solutions of weaker poisons. As a general rule, filter 

 paper and potato starch grains exert a more marked modifying action 

 than the denser bodies, such as sand, glass or paraffin. 



Breazeale (1906) tested the same point with extracts of certain soils 

 which proved toxic to wheat seedlings grown in them as water cultures. 

 The toxicity was wholly or partly removed by the addition of such 

 substances as carbon black, calcium carbonate or ferric hydrate. Other 

 experiments showed that the toxic substances of ordinary distilled water 

 are removed by ferric hydrate and carbon black, and further that the 

 latter substance will take out copper from copper solutions, rendering 

 them far less poisonous. 



Further corroboration of True and Oglevee's work was obtained by 

 Fitch (1906) who worked in a similar way with fungi, arriving at the 

 general conclusion that insoluble substances in a solution act as agents 

 of dilution or absorption whereby poisonous ions or molecules are in 

 some way removed. He found that n/256 of copper sulphate in beet 

 concoction exercised a stimulating effect on Penicillium glaucum, but 

 the addition of fine glass to the solution increased the stimulation, 

 while large or medium sized pieces did not have the same effect. 



This action of solid bodies in reducing the deleterious effects of 

 poisonous solutions is attributed to the process of " adsorption " whereby 

 a layer of greater molecular density is formed on the surfaces of solids 

 immersed in solutions. The solids presumably withdraw a certain pro- 

 portion of poisonous ions or molecules from the body of the solution 

 (retaining them in a molecularly denser layer over their own surfaces), 

 so that the toxic properties of the solution are reduced owing to the 

 withdrawal of part of the poison from the field of action. In some cases 

 this reduction may be so great as to relieve the solution of its toxic 

 properties, or even to cause an abnormal acceleration to replace a 

 marked retardation. Also, if the solution is of such a dilution as 

 to cause acceleration of growth in plants, the addition of insoluble 

 substances may increase this acceleration. The progressive addition of 



