20 LETTEES OF BEEZELIUS 



the surface of the liquid). To convince yourself of 

 this extraordinary phenomenon, take an iron wire, 

 one end of which has been tempered by heating. 

 Bring the unheated end into close contact with one 

 end of another ordinary iron wire. If you now put 

 first the heated end of the first wire and then the 

 other end of the second wire into the acid, the latter 

 will not be attacked by it, even if the contact between 

 the two wires is destroyed. The second wire, having 

 thus become passive, can communicate the condition 

 to a third, and this to a fourth, and so on, provided 

 that the wires are brought into contact within the 

 liquid in the manner described. In order to prevent 

 any misunderstanding as to this second method of 

 rendering an iron wire inactive, I give a detailed 

 account of the way in which the experiment is to be 

 carried out. The ordinary wire, which has thus been 

 made indifferent to nitric acid, and which for the 

 sake of simplicity I will call " secondarily indifferent," 

 is taken out of the acid, and, at any point which has 

 not been immersed, brought into contact with another 

 iron wire. The end of the secondarily indifferent 

 wire is then placed in the acid ; and finally the end 

 of the other wire. Both wires now remain passive in 

 the liquid, always supposing that the temperature 

 does not rise above 70. For the sake of complete- 

 ness I must add that an iron wire which has been 

 immersed in nitric acid of specific gravity 1-5 is like- 

 wise indifferent to the acid of specific gravity 1'36. 

 A third phenomenon of interest is this : if an iron 

 wire, which has been made indifferent to nitric acid 



