90 PHILOSOPHICAL TRANSACTIONS. [aNNO 1757. 



before the mixture. A small quantity of this limpid water being taken, it would 

 afford no tincture with galls. It was then all poured off, except so much in the 

 bottom of the glass as contained the above-mentioned clouds : to this some galls 

 were added, which in half an hour turned these clouds from a light yellow to a 

 deep red colour, but did not change the colour of the water, in which they swam. 

 10. Immediately after the affusion of ol. tart. p. d. to the water, galls were 

 added to the mixture, which tinged it of a deep and bright red colour. After 

 standing for some time, red clouds precipitated to the bottom, and the water 

 continued of a dusky opaque red colour. 1 1 . There is a small brook, formerly 

 mentioned, which runs near by these springs ; into which the water, that flows 

 from them, is discharged. He observed the stones and channel of this brook all 

 tinged with ochre of a deep yellow colour, so far up as the water of these springs 

 flowed into it ; but the channel, which the mineral water ran over before it was 

 mixed with the water of the brook, was very little or nothing discoloured with 

 ochre. As he conjectured what this was owing to, he afterwards took 2 equal 

 quantities of the mineral water, into one of which he put an equal quantity of 

 common water. In 1 hours the mixture became less transparent, and appeared 

 yellowish, while the simple mineral water retained its clearness. Next day there 

 was much ochre separated from the mixture, which subsided to the bottom of the 

 glass: but -the unmixed mineral water remained still clear and colourless, as 

 at first. 



All chalybeate waters separate their ochrous parts, when exposed some time 

 to the air ; but this separation is made sooner by the commixture of several 

 kinds of salts. Thus we see the ochre in this water is immediately separated 

 and precipitated by the solution of saccharum saturni. The oil of tartar causes 

 a precipitation of these ferrugineous parts in the same manner. Which parts 

 must be the sole cause that the water receives a tincture from galls ; since, after 

 they are precipitated, it loses that quality, which they notwithstanding retain 

 even after they are separated from the water. This precipitation of the ochrous 

 parts of the water were the only visible effects that Mr. W. could perceive follow 

 from the affusion of the ol. tart. p. d. He remembered indeed, when he was 

 at Moffat, to have seen the ms. of Dr. Horsburgh's experiments on this mi- 

 neral water, which apj^eared to be very accurate ; and which he understood were 

 afterwards printed, in a vol. published by the Phil. Society at Edinburgh. 

 Among these he observed one, which he thought so very remarkable, that he 

 particularly adverted to it. It was the effects of the affusion of ol. tart. p. d. to 

 the water, producing in it clouds, or a coagulation of a green or grass-green 

 colour. He thought these were the words ; and he owned he was something 

 surprised at them. A solution of vitriolum martis, mixed with this alkaline oil, 

 does indeed produce a green coagulum : but he could scarcely think that this. 



