VOL. L.J PHILOSOPHICAL TRANSACTIONS. Qi 



or any other chalybeate water, contained so large a proportion of that vitriol as 

 to be sufficient to produce these effects, when he considered that so many 

 writers, which he had seen upon this subject, had al! failed in their attempts of 

 extracting conspicuous martial vitriol from such mineral waters. He had tried 

 this experiment on 4 or 5 chalybeate springs in Scotland, and likewise on the 

 Spa and Pyrmont waters, which had been well preserved ; but there never re- 

 sulted any such effects from the mixture of these with oil of tartar as are related 

 in the above experiment. All the alteration it produced in these waters was the 

 precipitation of an ochrous earth, but without the least appearance of any green 

 colour. As he looked upon this as a leading experiment in the history of vi- 

 triolic waters ; as he had often tried it, and as often seen the green coagulum 

 produced with the solution of the factitious vitriol, and never could observe it 

 produced in any of the above water ; he began to suspect that these waters were 

 either not possessed of a vitriolic salt at all, or else that it was in some respects 

 very different from the factitious vitriol. For these reasons Dr. Horsburgh's 

 experiment appeared very extraordinary ; though at the same time he was greatly 

 pleased that he should have the opportunity of repeating it, and of observing 

 those phenomena in this ferrugineous water, which he had sought for in vain 

 in several others. But when he came to make the trial, he was yet more sur- 

 prised when he found it fail, and that the ol. tart. p. d. produced no green 

 colour or coagulum in this mineral water, nor caused any other alteration in it 

 than the separation of a large quantity of ochrous earth of a yellow colour, 

 exactly the same with what he had observed in the other steel waters. This 

 failure made him immediately conclude that he had committed some error in 

 the experiment : and though he was pretty sure that the mineral water, which 

 he had used in it, was quite fresh, yet he could not be so positive as to the oil of 

 tartar which he suspected to have been long kept. Yet that this could have 

 been the cause of his being so unsuccessful he could scarcely believe, though 

 indeed he could assign no other. 



When galls are added to the water at the same time with oil of tartar, instead 

 of its deep blue colour it affords only a red tincture. 



It appears from the 11th experiment, that an addition of common water 

 causes the mineral water to precipitate its ochre ; and the reason of this is ob- 

 vious : for if these ochrous parts be altogether terrene, as they appear to be, and 

 exist in the water unconnected with any other principle, then it must happen 

 that as these parts are uniformly diffused through the water, in which they are 

 suspended as in a menstruum ; by the addition of common water, this menstruum 

 being diluted, the cohesion of these terrene parts must be thereby weakened, 

 and their contact destroyed, so that their menstrual equilibrium being thus taken 



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