WATERS from ICELAND. toj 



changed from red to purple, with a very fmall tendency to- 

 wards the red. This mewed that the quantity of fait of tartar, 

 which had been added, was exactly 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 mod dif- 

 cernible and fatisfaclory fign of exact 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 fait of tartar as faturated one 

 grain weight of the largely diluted acid. 



The 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 fait of 

 tartar; the remainder is gr. 91.68. From this quantity, how- 

 ever, we mult make another deduction ; for, as Profeflbr 

 Bergman jufhly 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- 

 dueled 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, I 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, 



