16 Mr, Cavallo’s Magnetical 
apparatus boiling water was poured into the veffel. wherein the 
magnet ftood, in confequence of which the needle went back 
two degrees and a half. Some time after, when the water 
was quite cold, the needle was found nearer to the magnet, but 
not fo near as it ftood before the hot water was poured into the 
veffel. 
Next to the effects of heat, I was defirous of trying what 
could be effected by decompofing the iron ; and for this pur- 
pole an earthen veffel, containing about two ounces of iron 
filings, was placed near the fouth end of the needle of the 
compafs, by which the needle was drawn a little out of its 
natural direction. Having marked where the needle now flood, 
fome water firft, and then fome vitriolic acid, were poured upon 
the filings, which occafioned a brifk effervefcence, and a co- 
pious production of inflammable air; but foon after the begin- 
ning of the effervefcence, I was furprifed to obferve, that the 
needle came nearer to the veffel, ftiewing that the attraction 
between the needle and the filings had been increafed by the 
aCtion of the vitriolic acid upon the latter, which is contrary 
to what could have been expeCted ; for if we confider that the 
power of a magnet is diminifhed by heat, and that red-hot 
iron has either no attraction at all, or an exceedingly fmall 
degree of it, towards the magnet, we might have concluded, 
that the aCtion of the vitriolic acid upon iron would imme- 
diately diminifh its attraction, befides the other ffrong reafon 
arifing from the dephlogiftication of the iron occafioned by the 
effervefcence ; and in faCt fome time after, when the violence 
of the effervefcence, and of courfe the production of inflam- 
mable air, begins to abate, the attraction between the needle 
and the filings begins likewife to diminifh ; and at laft, when 
the effervefcence is hardly perceptible, the needle is found to 
ftand 
