VOL. XVII.J PHILOSOPHICAL TRANSACTIONS. 4QJ 



The usefulness of this experiment is not to be estimated only by the examen 

 it helps us to make of dulcified sea-water, but much more by the estimate, that 

 by its means may be made of natural fresh waters, whether of springs, rivers, 

 clouds, lakes, wells, &c. For it being generally granted, that those waters, 

 caeteris paribus are the best, both for the wholesomeness and divers economical 

 uses, as washing, brewing, &c. that are freest from saltness, which is an adven- 

 titious, and in most cases a hurtful quality in waters ; by this way of examining 

 these liquors, an attentive eye may soon discover whether there be any latent 

 saltness in them ; and may enable us especially by the help of a little practice, 

 to give a near guess how much one water is fresher than another ; and having 

 once attentively marked what change 4 or 5 drops, for instance, of our dis- 

 covering liquor, will make in two or three, or some other small determinate 

 number of spoonfuls, or rather of i ounce of water; it will not be difficult to 

 make a near estimate, whether any natural water proposed to him, have a 

 greater, an equal, or a less degree of freshness or saltness, than that water 

 chosen for the standard ; and how much the proposed liquor is more or less free 

 from saltness, than the other.* 



pression) when the solution has time enough allowed to diffuse itself through a great quantity of 

 water, the saline parts are thereby so diluted and weakened, that they are no longer able to sustain 

 the mineral corpuscles, they kept swimming before, but make with them and the water a confused 

 and subsiding mixture, usually of a whitish colour. This may appear whan the butter of antimony 

 being put into common water, is thereby quickly and plentifully precipitated in the form of that 

 white powder, which chemists call mercurius vitae. To which I may add, that I have also produced 

 a powder of that colour, by pouring into common water a strong solution of tin glass made in aqua- 

 fortis. And by the same way we have precipitated the tincture for solutions of the finer parts of 

 jalap, benjamin, true labdanum, antimonial sulphur, and divers other bodies made in vinous spirits. 

 If it were not for this power, that water has to weaken most solutions of bodies, I could have em- 

 ployed, instead of that silver, either quicksilver dissolved in aquafortis or lead crude, or calcined in 

 the same liquor, or (which is more convenient) in strong spirit of vinegar; since these, and some 

 others, are found to be prscipitable by salt-water into whitish powders. But though a very heedful 

 observer may for a shift, make use of these metalline solutions, to guess at the quality of water, as 

 to freshness and saltness, yet the precipitation that is made by dilution is not difHcult to be dis- 

 tinguished from that which is performed by a true and proper precipitaBt, (as in our case by the 

 common salt, that is harboured in the pores of the water) both by the quickness of the effect, and 

 the copiousness of the white substance produced, and on both those accounts is very much inferior 

 to it. — Original. 



* The author hints in a note that his precipitant " may much assist men to discover whether a 

 mineral water proposed to be examined do or do not contain some saline substance ; and if it do, 

 whether it contain it copiously or not. This I have tried (he adds) upon more than one of our 

 English mineral waters, and thereby found, that one that is reputed of another nature, contained 

 pretty store of saline matter ; and that another is impregnated with a surprising plenty of a saltish 

 lubstance." 



VOL. III. 3 S 



