in some Artificial Manures. 109 



to pay about seven pounds for the same quantity. This ore of 

 iron contains almost invariably more or less arsenic, which passes 

 into the sulphuric acid manufactured from pyrites ; whereas the 

 native sulphur containing little or no arsenic, the sulphuric acid 

 made from it is not so liable to be contaminated with that poison- 

 ous substance. Pyritic sulphuric acid, on account of its being 

 much cheaper, seems in a great measure (at least in Dublin) to 

 have taken the place of that manufactured from native sulphur ; 

 and hence the occurrence latterly of so much arsenical sulphuric 

 acid in commerce, and the presence of arsenic in so many sub- 

 stances in the preparation of which that acid is directly or indi- 

 rectly employed. 



The vitriol and manure manufacturers have been in the habit 

 of making an inferior kind of pyritic sulphuric acid, which, owing 

 to its dark colour, is termed brown sulphuric acid : this contains 

 a comparatively large proportion of arsenic, and is chiefly used 

 in making superphosphate and other artificial manures ; and the 

 manufacturer appears to think that the acid which is too impure 

 to be used in the arts, is good enough for making manui'es 

 and for other agricultural purposes. This, however, from the 

 experiments I shall presently refer to, appears to be a great 

 mistake. 



Knowing that sulphuric acid containing arsenic was so largely 

 employed in making superphosphate and other artificial manures, 

 and that they therefore must contain variable quantities of that 

 substance, I have for some time thought that it was not impro- 

 bable that plants grown with such manures might imbibe or take 

 up from the soil where those substances had been employed, a 

 certain quantity of arsenic, and in this way be rendered more or 

 less unwholesome as articles of food. 



As a preliminary experiment to ascertain if plants had the 

 power of taking up arsenic when it was presented to their roots 

 in the soil, I transplanted into a flower-pot, in June 1857, three 

 small plants of peas, and when they had recovered the trans- 

 planting, I commenced watering them every second or third day 

 with a saturated aqueous solution of arsenious acid; and this 

 treatment was continued for more than a week without its ap- 

 pearing to exercise any immediate injurious effects on the plants. 

 At this time, however, I was obliged to leave hotne for some 

 months, so that I was unable to continue longer the watering 

 with the arsenical solution, or to observe further its effects on 

 those plants. On my return I found that they had grown to 

 about their full size, had flowered, and produced seed, showing 

 that arsenic, though so very destructive a substance to animal 

 life, liad not apparently exercised any decided injurious effects 

 on those plants. 



