456 Copeland and Kahlenberg , 
2. The specific toxicity of the metal when in solution in form 
of such salts. 
There is another possible factor — (3) the nature of the com¬ 
bination formed. But it is not probable that this has made any 
difference in any of our experiments, except in the case of mag¬ 
nesium, which decomposes water and makes a solution so alkaline 
that the concentration of OH ions must be fatal. The rapidity 
of diffusion of the solution is still another factor when the plants 
and the metals are separated in the water, and the solution is 
not disturbed: in the cases of iodine, arsenic, and copper (Table 
IV, copper wire) this was apparent. 
Preliminary experiments were made upon Lupinus luteus and 
Zea Metis, without equal areas of metal or equal volumes of 
water. As more accurate work was afterward done with Lupi¬ 
nus albus , the experiment with L. luteus is not reported. The 
remaining experiments were performed in uniform glass beakers 
of 200 c.c. capacity, which were coated with paraffine to re¬ 
move even the suspicion that the glass had influenced the re¬ 
sults. As many of the metals as were available in the form of 
foil, or as could be rolled, were used in that form; and pieces 
were cut out for use 57 by 34 mm., exposing an area of 3,876 
sq. mm. These pieces were bent so as to stand on edge on the 
bottom of the beaker. Zinc wire was rolled flat and bent into 
a coil having the same area as the other metals, and reaching 
about the same height from the bottom of the beaker. A mag¬ 
nesium coil was used in the same way. Antimony and bismuth 
were used as sticks, of which enough were used to have the de¬ 
sired area; and these were tied so as to stand about as high as 
the other metals in the water. All of these metals then offered 
equal surfaces to the action of the water at practically the same 
distance from the roots. Roll sulphur and carbon (in the form 
of a plate cut from conducting carbon such as is used in bat¬ 
teries), though not metals, were experimented with under the 
same conditions. Mercury could not be employed except as a 
layer on the bottom of the beaker, whose surface exposed to the 
water was about 2,000 sq. mm. Arsenic and iodine were used 
as a coat of flakes over the bottom of the beaker, but the sur¬ 
face actually exposed to the water was of course much greater 
