The Contents of Some Letters from Two Learned and Curious Observers in Staffordshire, concerning the Sand Found in the Brine of the Saltworks of That Country &c. Sent to the Royal Society by Dr. Rob. Plot. S. R. S.

6. The Contents of some Letters from Two learned and curious Observers in Staffordshire, concerning the Sand found in the Brine of the Saltworks of that Country &c. sent to the Royal Society by Dr. Rob. Plot. S. R. S. Having had occasion about half a year since to consider the Brines whereof we make our white Salt here in England, and more particularly those of Staffordshire; I consulted amongst others that instructive discourse of Mr. John Collins concerning Salt and Fishery then newly publish't; wherein finding Pag. 52. that those great quantities of Sand met with in all Brines, whether of Pits, made of Sea liquor, or by melting of foreign Salts, are not in the Brines before they are boyled, but produced by a sort of petrification during the Evaporation; which he confirmes by the Experiment of strong Brines having been dreyned or squeezed through most pure fine Holland of eight foldings, and no symptoms of any Sand being left in the Filter: I thought it of concern to me (though then at a great distance myself) to have the Experiment repeated upon the Staffordshire Brine, not only because of the particular account I was then giving of it, but rather for the sake of the great quantities of Sand I knew to come from that Brine, which I was inclin'd to believe would either quite overthrow, or mightily confirm the truth of that odd Phenomenon. Whereupon I made bold to request the assistance of two Curious Observers, Neighbors to these Brine-pits, to make the Experiment, who were so very nice in performing it, that to the eight folds of fine Holland, they added as many more of finer Cambrick, through both which though they strained a competent Quantity of the brine, yet found nothing left in this very close Colander, but a little black dust, which they imputed only to the foulness of the Water, it being nothing like Sand; for having examin'd the Cloath both with their fingers and the Microscope, they could feel or see no more of Sand than if they had percolated the clearest Spring waters; and yet this brine is found to hold in boiling at least 1/2 of as much Sand as Salt. i.e. the Brine that suffices to make a bushel of Salt, yeilds also at least a Peck of Sand. But notwithstanding this Experiment, it did not seem to their apprehensions necessary that the Sand should be generated in the boiling, but might rather be originally there; for before they strained it, they observed in the water (by the help of a Microscope) a great multitude of very minute Animals (much smaller than those in pepper-water) swimming about in it, together with many small transparent plates, some of them a little bigger than the Animalcule's, and some less, but all of a rectangular oblong figure, though some indeed seem'd very near a square, which they found also in the water after straining as thick as before. Nor did they wonder at it, because the pores or rather interstices between the threads of the Holland and Cambrick, though they were extremely fine, appear'd in the Microscope to be exceedingly (they affirm'd they might safely say twenty times) greater than either the Animalcule's or Plates. And these they judged to be the original particles both of the salt and Sand, which as the Water evaporates in boiling they thought might gather together till they made up such a visible course body as we see the greater Cornes of each are. Wherein they were confirmed in a little time, for observing with an excellent Microscope some Some of the strong Brine which drops from the Baskets or Vessels when the Salt is first put into them, though at first it look't like clear water, yet upon a more accurate observation it appeared exceeding full of these oblong particles, which as they look't on them, they could sensibly perceive to gather together and club to make greater parts, and as the water dried off from the glass to grow far larger and larger till they appeared as big, and not much unlike a large sized Table Diamond: Which made them guess that the Sand might be also generated (if I may so say) after the same manner, it appearing to them to be nothing (pardon the expression) but an insipid Salt composed of parts not so sharp pointed as the other, but rounder and blunter angled, and consequently not so pungent on the Tongue. Which point they believed might be cleared perfectly if some of the Sand were dissolved in fair water, and that water examined afterwards by straining or otherwise to see if any, or all the Sand, would be left behind &c. Whereupon having some of the Sand by me I endeavoured accordingly to dissolve it in fair water, to see whether I could reduce it again into its former state, but without success; its parts being so inseparably fix't that they would by no means dissolve: I also tryed the Salt, which though it dissolved yet would not render itself again into plates. Whereof sending an account to my friends in Staffordshire: they were pleased also to make a further trial of dissolving the Sand separated from the Salt in boiling; which though they confess they could not do to any considerable Quantity, yet they found that after the straining, it was not so heavy by a great deal as before, the water that came from it being very clear, which made them believe that it did dissolve in some measure, unless (as is very probable) there were in the Sand some particles of Salt, which upon dissolution were separated from it, it, and so render'd it lighter: Nevertheless they did not doubt but a great part of the Sand might also be dissolved though perhaps no great quantity in Pump-water in which it seems they tryed it. But there has no further Experiment yet been made, wherefore if the Royal Society please to send me any instructions for a further tryal, they shall be carefully transmitted, and I dare promise them as carefully executed. What those Gentlemen's opinions are concerning the Animalcula they do not tell me, what my own is concerning those matters, it shall suffice in general to acquaint you that I think they may perhaps may be analogous to the Eels in Vinegar, the rest you must expect in my Natural History of Staffordshire now in the Press. I shall add no more but that one of the aforesaid Gentlemen since the account above mentioned casually looking upon some of the Salt made at those pits before it was dried and beaten small, observed that many of the larger Cornes were of the same shape to the naked Eye, as the minute ones appear'd of in the Microscope, and that they were visibly made up of a great number of small plates, shooting up from a quadrangular oblong Base into a very obtuse Pyramid, hollowed within. Which is all at present but my duty to the Society, and that I am Their most Faithful Servant, R. P. I. Hor.