VOL. L.] PHILOSOPHICAL TRANSACTIONS. 8<) 



From these experiments Mr. W". observes, that the colour which these waters 

 afford with galls and pomegranate-flowers, is very uncommon. The more iron 

 any mineral water contains, it will afford the deeper colour with such astrin- 

 gents : but though he had tried this experiment on many of the ferrugineous 

 waters in Scotland, and also on the water of some of the foreign spas, he 

 never observed one that afforded so deep a colour as this. Some of the weakest 

 of them gives only a red or faint purple tincture, and the strongest only a deep 

 purple : but he never saw or heard of any chalybeate water, but this, either in 

 Scotland or elsewhere, that afforded an intense black and inky colour with galls. 

 From which, he thought he might venture to conclude, that the water of this 

 spa contains a far larger proportion of iron than most, or perhaps than any other 

 chalybeate water hitherto discovered: and for this reason, he supposed it would 

 likewise be so much the more preferable to most others in medicinal virtues ; 

 which had indeed appeared by many surprising cures it had performed, and which, 

 he was persuaded, would more fully appear, when its medicinal effects should 

 be better known. There must he thinks, be a great quantity of iron in this 

 water, when it yields as deep a colour with galls as a strong solution of sal 

 martis. He was indeed at first apprehensive, that this perhaps might not be 

 owing so much to a large and uncommon proportion of chalybeate parts, as to 

 the commixture of alum, which he judged to be in the water. But we see the 

 contrary appears by these trials : for alum of itself affords no tincture with as- 

 tringents, and, instead of rendering a solution of sal martis with galls of a more 

 intense colour, it rather makes it lighter and more diluted. 



As there is an ochrous earth separated from all steel waters, when exposed to 

 the air, which subsides to the bottom, and a metalline scum or cremor, which 

 swim on their surface ; he next considers the appearances which they make in 

 this water. 



Eocp. 8. A solution of saccharum saturni being dropt into common spring- 

 water, left the upper parts of the water clear and colourless, but formed a lac- 

 tescency towards the bottom. The same solution being added to the mineral 

 water, soon turned it of a turbid yellow colour, which afterwards subsided, and 

 formed a deep yellow cloud in the bottom of the glass ; and below this yellow 

 sediment there adhered to the bottom of the glass a whitish substance, which he 

 took to be the metalline parts of the saccharum saturni separated from the purer 

 parts of the salt, which were still suspended in the water, and which made it of 

 a muddy whitish colour. 9. Forty drops of oleum tartari per deliquium being 

 added to 1 oz. of the water, made it of a uniform light yellow colour ; but in an 

 hour afterwards there were many small yellow terrene nubeculae formed in it. 

 These the next day were more conspicuous, being thoroughly separated from the 

 water, and precipitated to the bottom, leaving the water quite clear, as it was 



VOL. XI. N 



