20 
Mr. Cavallo’s Magnetic al 
experiments hitherto made, the variety in the fhape or bulk of 
the iron or fteel may have occafioned a confiderable difference. 
After the refult of thofe experiments, it was natural to exa- 
mine the effect which other acids might have on iron and fteel ; 
therefore the above-mentioned experiment of the fteel wire 
was repeated with nitrous inftead of vitriolic acid ; the refult of 
which was that the attraction between the magnetic needle 
and the wire was increafed, but not lo much as when vitriolic 
acid had been ufed. Here follows the particular account of 
the experiment. 
About fix vards of clean fteel wire, near one-fiftieth of an 
inch in diameter, being twitted in various directions, was 
placed in the ufnal veflel near the fouth end of the needle ; in 
confequence of which the needle was attracted from its natural 
fituation, viz. from 283° 3a 7 to 282° 50’. About two ounces 
of water were then poured over the wire, and immediately 
after, near one ounce of nitrous acid was added, which 
produced an efferveicence : the magnetic needle, however, 
hardly moved from its former fituation ; but in about a minute’s 
time, the effervefcence being increafed very much, the needle 
came to 282° 42b About a quarter of an hour after, the vio- 
lence of the effervefcence abated a little, and the needle went 
back again to 282° 50b A fhort time after, it flood at 283° 
2b At lad, when about half an hour had elapfed fince the 
beginning of the operation, the effervefcence was hardly per- 
ceivable, the liquor was become red like the colour of red 
ochre, and the, needle flood at 283° 1 3b viz. farther from the 
veflel than it did before the acid was added to the wire. 
It appears, therefore, that the effervefcence occafioned by the 
nitrous acid produced a fimilar effedl, though not in fo great a 
degree as the vitriolic. The maximum of the attradlion feems 
to 
