WATERS from ICELAND. 125 



rected with force to tliofe parts of the fcattered fediment which 

 are more difficultly moved. Having thus condenfed the fedi- 

 ment as much as pomble, the filtre is left in a cool place to dry. 

 When it is perfectly or nearly dry, I fpread it flat on a table, 

 and cut away all that part which was foaked with tallow, and 

 and alfo thofe parts of the clean paper to which the fediment 

 does not adhere. The reft, with the fediment on it, is then 

 well dried before a fire, and weighed, and the weight of it 

 marked down ; and, laftly, in order to know how much of 

 this weight is made up by the paper, I take care, before I pre- 

 pare the filtre, to chufe another piece of the filtrating paper, 

 equal in thicknefs to the one of which the filtre is made. This 

 equality of thicknefs is judged of by holding the two pieces 

 between the eye and the light ; or, for greater fecurity, bits of 

 the two pieces may be cut off, exactly fimilar and equal in 

 form and fize, and J their weight compared, and allowance may 

 afterwards be made for their difference of weight, if there be 

 a difference. After weighing the bit of paper with the fedi- 

 ment on it, a proper bit of the referved paper is laid flat on a 

 fmooth table or plate of glafs, and the paper on which the fedi- 

 ment had been collected is laid over it, with the clean fide un- 

 dermoft ; then a bit of card, fomewhat lefs, but nearly of the 

 fame form, is preffed down on both the papers, and, with a pair 

 of fharp pointed fciffars, or a pen-knife, the undermoft paper is 

 cut exactly to the fame fhape and fize as the uppermoft, and is 

 afterwards weighed. TW weight of it being deducted from 

 that of the former, we thus learn the weight of the fediment, 

 with a greater degree of exactnefs, and with lefs trouble, than 

 by any other method which I have been able to contrive. To- 

 complete this article, I beg leave further to add, that the 

 mod ready and convenient way to foak the margin of the fil- 

 trating paper with tallow or wax, is to hold it above a lighted 

 candle, at a proper diftance for warming it a little, and then 

 melting the end of another candle, apply it immediately to the 



warmed 



