four milk or whey, in fome place ready to wash the part affected well with it, which will quickly deftroy the poignancy of the lime, and prevent the mischief that would otherwife arife from it. The fourer the milk or whey is, the better it will be for this purpofe; it ought therefore to be long kept. For want of this, vinegar will produce the fame effect, or very ftale urine will be of ufe; but the milk or whey is the cheapest and best remedy, and ought to be always in readiness. POSTSCRIPT, $1. In the preceding effay, I have fuppofed that no other abforbent* earth is ever mixed with the calcareous in any fort of limeftone; *Abforbent earths are all thofe that unite with acids, of which there are feveral varieties; calcareous earths being one of these, ftone;-because, in fact, if ever any of these are mixed with the calcareous in these subftances, they are in fuch fmall proportion as not to be worth regarding.Thofe, however, who want to be critically exact in their analysis of lime-stone, may discover if there is any other fort of absorbent earth con tained in it, by dropping into the filtred folution obtained by the procefs, $12. p. 408; a few drops of a clear folution of volatile alkali.If no turbidness enfue, the calcareous earth has been pure. If any precipita tion takes place on adding the alkali, drop more, and more, till no turbidnefs arifes, then filtre the whole;-what remains in the filtre is abforbent earth that is not calcareous. For acids attract volatile aikali more strongly than any of the abiorbent earths, except the calcareous clafs alone. $2. § 2. It may oftener happen, that a confiderable proportion of gypfum may be united with lime-stone in the fame quarry; and, as this fubflance would greatly alter the nature of the lime as a cement, (fee p. 335.) and would probably affect it as much as a manure, it is of more importance to inform the reader of the eafieft way of discovering this fubftance when it is prefent in limeftone. It has been already said, that gypfum is a compound, confifting of the vitriolic acid and calcareous earth; and, as the vitriolic acid attracts this earth more ftrongly than any of the other acids, this compofition is not in the leaf affected by either the nitrous or muriatic acids. . Hence, it follows, that if gypsum shall be be contained in any calcareous mafs examined by the process described § 12. p. 408. it will remain untouched by the acid, and be found in the filtre, after the calcareous earth diffolved in the acid fhail have paffed through it, forming a part of the refiduum. Take this refiduum, therefore,-add to it nearly its own weight of fixt alkali * previously diffolved in a confiderable quantity of water, and filtred;-digeft it in a warm bath, or even boil it for fome hours ;-pour the whole into a filtre while yet warm ;-as the fluid paffes through the filtre, pour upon it more boiling water ;-as that paffes off, continue to add more water, till it comes through the filtre quite infipid and pure, and then let it run off entirely. By this process, the vitriolic acid leaves the calcareous earth to unite with the fixt alka li, Potash. li, (to which it has a ftronger attraction), and with it forms avitriolated tartar;—this vitriolated tartar, and the fuperfluous alkali, are diffolved by the water, and carried through the filtre along with it, fo that what remains behind is the earthy part of the gypfum, and the heterogeneous matters contained in the original lime-ftone. By pouring upon this refiduum, therefore, fome nitrous or muriatic acid, and treating it as directed, 12. p. 408. the calcareous earth that was in the gypfum, will be now entirely diffolved; fo that, when it is filtred and dry, the difference between the weight of this refiduum, and what it formerly was, is the real weight of the gypfum originally contained in the lime-ftone. N. B. If the alkali employed to decompofe the gypfum was in a mild state, the calcareous earth that remains, will effervefce ftrongly when it is diffolving in the acid;but, if a caufic alkali has been employed, the |