70 hedgcock: injury by smelter smoke 



which is slightly higher than the ratio (0.84998) of the present 

 atomic weights. All sources of error have been carefully examined 

 and are critically discussed in the full paper. None, however, are 

 believed to be sufficient to account for the difference between 

 this value and the ratio of the present international atomic weights. 

 Using the results of the silver voltameter to measure the 

 coulombs passing through the circuit according to the decision 

 of the London Electrical Conference (1.11800 mg. of silver = 1 

 coulomb) the electrochemical equivalent of iodine is: 



1.31502 mg. per coulomb. 



The value of the faraday on the basis of the present internation- 

 al atomic weight of iodine (126.92) and the foregoing value of the 

 electrochemical equivalent of iodine is: 



'- = 96,515 coulombs. 



0.00131502 



The value of the faraday derived from the atomic weight of 

 silver and the defined electrochemical equivalent of silver is: 



107.88 



0.00111800 



= 96,494. 



The mean value of the two is 96,504, but we recommend for 

 general use the round number 96,500. 



PLANT PHYSIOLOGY. — Injury by smelter smoke in southeastern 

 Tennessee. George Grant Hedgcock, Bureau of Plant 

 Industry. Communicated by Karl F. Kellerman. 



Observations were made on the condition of the vegetation in 

 the region surrounding Ducktown and Copper Hill, Tennessee, 

 in the neighborhood of the copper smelters during the month of 

 September, 1913, before any frost injury had taken place. The 

 area affected by the acute form of injury is probably larger than 

 it was during 1905 and 1906 when J. K. Haywood^ of the Bureau 

 of Chemistry made studies of the effects of the smoke in this 

 region. The actual damage by acute injury at present is possibly 

 slightly less, owing to a greater area of smoke diffusion, but is 



1 U. S. D. A. Bur. CJaem. Bui. 113, pp. 13, 1908. 



