344 USE OF ARSENIC 1N HORTICULTURE.  [Sess. uxxu. 
illustrates one of the dangers attending the use of arsenic in 
horticulture. 
It seems perfectly evident that though the arsenic when 
put upon the ground is held in solution by the addition of 
an alkali, it is not washed away as the alkali is, but remains 
fixed in the soil so as to be dangerous for a lengthened period. 
In one case hens were poisoned by arsenic from a pathway 
two years after it had been treated with arsenical weedkiller. 
I have not definitely ascertained in what form the arsenic 
exists in the soil. Very possibly the alkaline solution may 
be neutralised by the humic or other acids in the soil. This 
particular soil contains a distinct percentage of iron, and 
there are indications that the arsenic has probably formed 
a compound with the iron which is insoluble in water. 
However that may be, the important point is that it is 
present in quantity sufficient to render it highly dangerous. 
Another no less important point is that the presence of 
the arsenic in such quantity appears to have no effect at all 
in preventing or retarding the growth of the weeds. From 
experiments I have made, I find that weeds are speedily and 
completely killed by watering them with a solution of any 
alkaline carbonate, chloride, or hydrate. Common salt and 
washing soda effectually kill weeds. The addition of arsenic 
does not appear to add any value to the remedy. Certain 
classes of plants, such as the maritime Chenopodiacee, are less 
easily killed by common salt, and I have been told it is less 
efficacious in such places as the Orkney and Shetland Islands, 
where the whole vegetation has become acclimatised to a 
saline environment. 
An aqueous solution of arsenic applied to weeds in dry 
weather is itself fatal to the exposed parts, but generally 
fails to kill the roots, and arsenic in the soil does not prevent 
the growth of plants. Its use in weedkiller seems founded on 
an impression that it will be more permanent in clearing out 
weeds than other applications. But arsenic, per se, does not 
appear to have any special virtue, and it is so dangerous to 
handle that it would be no loss to horticulture and a distinct 
gain to the community to have its use in this particular form 
prohibited by some legislation like the Poisoned Flesh and 
Poisoned Grain Prohibition Acts of 18635 and 1864. 
The serious dangers attending the use of arsenic in 
