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WATERS from ICELAND. 125 
rected with force to thofe parts of the fcattered fediment which 
are more difficultly moved. Having thus condenfed the fedi- 
ment as much as poflible, 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 ali 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 filtreis 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’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 prefled down on both the papers, and, with a pair 
of fharp pointed {ciflars, or a pen-knife, the undermoft paper is 
cut exactly to the fame fhape and fize as the uppermoft, and is 
afterwards weighed. T€ weight of it being dedudted 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 
moft 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 
