BOOK III. CHAP. VL ^jy 



any fucli effedl happens about the lead mines of Liguanea. This 

 merits a further inveftigation; and hkewife the fprings, or ftceams, 

 which pafs among them, ought to be carefully examined. It ap- 

 peared, from Mr. Mufchenbrock's experiment, that lead is the 

 fooneft rarefied of all metals ; its expanlion with the fingle flame of 

 a lamp being (compared with iron) as one hundred and fifty-five to 

 eighty: which is nearly double ; fo that its parts are evidently li- 

 able to be affected by a very fmall portion of heat. And we find, 

 that milled lead, when expofed to the a£lion of the fun in Jamaica, 

 by being improperly made ufe of, inftead of (heet-lead, for co- 

 vering gutters and valleys on the roofs of buildings, very foou 

 blifters, cracks, and becomes leaky. 



8. Allum. 



Waters which contain it difcover themfelves, on evaporation, by 

 their auftere, aftringent tarte. They change vegetable blues (as 

 fyrup of violets frefh-made) to a red colour ; but, if the fyrup is 

 old, to a green. An addition of lime-water deepens the green. 

 They alfo coagulate milk. Bricks harden the foftefl water, and 

 give it an alluminous impregnation. The pradice therefore of 

 lining w^ells with brick is fuppofed improper. 



But, on the other hand, about a quarter of an ounce of allum, 

 powdered, and thrown to every fix or feven gallons of turbid, 

 muddy water, will, in about an hour or two, render it perfecftly pure 

 and tranfparent. Nor does any inconvenience refult from the allum. 

 It is not only an excellent purifier of fuch water, but is thought, 

 in hot climates, to cool the body, and brace up its relaxed fibres. 



There are other methods likewife recommended for purifying 

 water. In Jamaica, the people of Spanifh Town keep their river- 

 water in feveral large jars, where it fettles and depofites a fediment 

 in about twenty-four or thirty-four hours. Some families have 

 three, or more ; which, being taken in turn, well cleanfed, and 

 replenhhed regularly, fupply them with a very pure and light 

 water inferior to none. 



Very foul water may be purified by letting it percolate through 

 fand flowed in half-puncheons, or tubs made on purpofe ; with 

 Imall holes two or three inches above their lower end, guarded 

 with a piece of hair-cloth, doubled on the infide, to prevent any 



Vol. II. 4 E of 



