j82 Mr. Keir’s "Experiments and Obfcrvations on 
neath the furface, and thus fubjects it to the adion of the 
acid. 
It is therefore with difficulty that thefe pieces of altered 
iron can be dried, without lofmg their peculiar property. For 
this reafon, I generally transferred them out of the folution ot 
liiver or concentrated nitrous acid into any other liquor, the 
effects of which I wanted to examine. Or they may be 
transferred firft into a glafs of water, and thence into the 
liquor to be examined. But it is to be obferved, that ii they 
are allowed to remain long in the water, they lofe their pecu- 
liar property or alteration. They may be preferved in then- 
altered ftate by being kept in fpirit of lal ammoniac. 
23. To a faturated folution of copper in nitrous acid (which 
was capable of being readily precipitated by fieffi lton^ J added 
lome faturated folution of filver. From this mixture a piece 
of frefh iron neither precipitated filver nor copper : nor did the 
addition of fome dephlogifticated nitrous acid effed this pre- 
cipitation. 
24. A folution of copper, formed by precipitating filver 
from nitrous acid by means of copper, was very reluftantly and 
{lowly precipitated by a piece or frefh iron , and the iron thus 
afted on by the acid was changed to an ochre. 
25. A faturated folution of filver having been partly preci- 
pitated by copper, acquired the property of acting upon rrefn 
iron, and of being thereby precipitated. 
26. Frefh iron immerfed fome time in folutions of nitre of 
lead, or of nitre of mercury in water, did not occafion any 
precipitation of the diffolved metals ; but acquired an altered 
quality, Thefe metals then in this refpedt referable filver. 
27. It is well known, that a folution of martial vitriol, 
added to a folution of gold in aqua regis 3 precipitates the gold 
in 
