TEST FOR IODIDE OP POTASSIUM. 
75 
the well had turned brown, and ultimately died, while all 
the rest remained perfectly flourishing. Assuming from 
these facts, that the common salt in this water was the chief 
cause of the results described, it is proved that water con- 
taining about 7 grs. of salt in each pint is, in its continued 
use, an effectual poison to the weaker vegetation ; or that 
when a soil is continually watered with a weak solution of 
salt, it gradually accumulates in it until the soil becomes 
sufficiently contaminated to be unfit to support vegetable 
life. In either case an interesting subject of inquiry is sug- 
gested — What is the weakest solution of salt which can pro- 
duce in any measure this poisonous effect ? or, in other 
words, at what degree of dilution does the danger cease? 
For salt is an important natural constituent of much spring 
water, quite independent of any infiltration from the sea, 
as in this instance. Thus, the water of the artesian well, 
Trafaigar-square, London, contains in each gallon about 20 
grs.; that at Combe and Delafield's brewery, 12.; that at 
Wolverhampton Railway Station, 6; one lately sunk at 
Southampton, for supplying a private manufactory, 40. 
May it not be asked, whether the subject of the suitable- 
ness of waters in general for the various purposes to which 
they are applied, be it in manufactures or for steam-engines, 
domestic purposes or drinking, is not worthy of a greater 
share of scientific attention than it has hitherto command- 
ed ? — Ibid. 
ART. XIX. — PHARMACOPCEIA TEST FOR IODIDE OF 
POTASSIUM. 
A Correspondent, D. B., of Aldersgate Street, has 
directed our attention to one of the tests described in the 
notes to the Pharmacopoeia {or Iodide of Potassium, which 
is thus expressed,—" Sulphuric acid and starch, added 
together, it becomes blue." " The truth is," says our cor- 
respondent <f that the above is a test of the impurity, not of 
