466 
Copeland and Kalileriberg. 
The elements wjiose presence in the water where plants grow 
has been shown to be always fatal, are thallium, cadmium, cop¬ 
per, cobalt, zinc, lead, iron, antimony, magnesium, arsenic, io¬ 
dine, tungsten, and tellurium. Mercury and silver seem to 
kill the Soja bean. It is not necessary, and might not be possi¬ 
ble, to demonstrate by chemical tests the presence of all of these 
substances in the roots they have killed. They had to be in the 
roots, where they could attack the protoplasm of each ceil, be¬ 
fore they could kill it. And in some instances the dead root’s 
appearance shows the presence of salts of the metal that killed 
it. Thus, roots killed by copper or -nickel, or iron or cobalt 
show colors characteristic of salts of these metals, while those 
killed by zinc, lead, thallium, and arsenic are at the darkest not 
more discolored than they would be if killed by heat. The ap¬ 
pearance of the root or of the metal, or of both, betrayed the 
presence of salts of every metal that was uniformly harmful. 
What literature there is bearing upon this question harmon¬ 
izes with our results as to the comparative toxicity of the dif¬ 
ferent elements: and as all other determinations, while agreeing 
with ours, have been made with the salts of the metals, we 
have in them still further support for the idea, that it is in or¬ 
dinary compounds, and not in any modification of the metallic 
form, that the metals in our experiments attack the roots. And 
this being so, we see absolutely no difference between this and 
any other ordinary case of poisoning. 
On the first factor in determining the injury a metal can do — 
its tendency to get into solution-—, we introduce from a table 
by Neumann (18. p. 229) the following sequence of basic ele¬ 
ments, arranged according to their solution tensions, as deter¬ 
mined by the differences in potential existing between the met¬ 
als and normal solutions of their salts: magnesium, aluminum, 
manganese, zinc, cadmium, thallium, iron, cobalt, nickel, lead, 
hydrogen, bismuth, arsenic, antimony, tin, copper, mercury, sil¬ 
ver, palladium, platinum, gold. Down to mercury, all of these 
elements except aluminum and tin and possibly magnesium, are 
injurious, and, excepting further manganese and bismuth, fatal 
during the time of experiment. Mercury and silver were some¬ 
times injurious; palladium, platinum, and gold, apparently never 
