WATERS from ICELAND. 105 
changed from red to purple, with a very fmall tendency to- 
wards the red.. This fhewed that the quantity of falt of tartar, 
which had been added, was exa¢tly fufficient for faturating the 
fuperfluous acid. Had the faturation not been fufficiently ex- 
act, I could have added a little more of the alkali, or a little 
more of the acid, as I had done in the fmaller effays which 
were preparatory to this; but the tint of colour which I had 
here produced, was that which I had found to be the moft dif- 
cernible and fatisfa@tory fign of exaét faturation, in former ex- 
periments ; and it is proper to mention, that one grain more of 
the largely diluted vitriolic acid changed this purple very re- 
markably to a more decided red, and that with one grain lefs, 
the hue of the purple, by being inclined to blue, would have 
been equally diftinguifhable ; of which I fatisfied myfelf, by 
adding as much of the folution of falt of tartar as faturated one 
grain weight of the largely diluted acid. 
TuE quantity of the diluted acid added at firft was 200 
grains. From this was to be fubftracted 108.32 grains, the 
quantity faturated by the 38.6 grains of the folution of falt of 
tartar ; the remainder is gr. g1.68. From this quantity, how- 
ever, we muft make another deduction ; for, as Profeffor 
Bercman juftly obferved, the infufion of litmus contains fome- 
‘thing which is of an alkaline nature, or is capable of faturating 
a. certain quantity of acid. To learn how much was to be de- 
daéted on this account, I tinged a fmall quantity of diftilled 
water, with the fame number of drops of the infufion of lit- 
mus that I had ufed in tinging the Iceland water, and: then 
making the diftilled water boiling hot, 1 began to add fome of 
the largely diluted vitriolic acid, and kept the water boiling all 
the time. The firft additions of acid, as I expected, did not 
produce a change of colour, or, if any change was produced, 
it foon difappeared again, while the water was boiling ; but as 
foon as I had added gr. 3.5, a permanent change was produced 
to a reddifh purple: This quantity therefore muft, in the next 
VoL. III. O place, 
