﻿of Zinc on Galvanized Iron, 1 33 



weighed when cooled. From this loss we may obtain with tole- 

 rable exactness the amount of zinc which remains, and which 

 immersion in mercury will not remove. 



This quantity of zinc appears to be combined with the iron, as 

 it does not volatilize, and becomes very imperfectly oxidized when 

 exposed for some time to a red heat under access to air. 



The existence of the zinc, after this treatment, may be shown 

 by the readiness with which the iron wire again takes up mer- 

 cury, and admits of being polished. The smallest quantity of 

 zinc remaining on the wire becomes immediately visible by its 

 lustrous appearance when rubbed after immersion in mercury : 

 when the whole of the zinc is removed, the wire ceases to give a 

 silvery appearance. The removal of the zinc immediately in 

 contact with the iron can only be effected by the oxidation of the 

 iron and zinc together. 



Repeated experiments prove that this quantity of zinc, which 

 is combined with the iron, can be readily ascertained from the 

 quantity of mercury which sublimes when the wire is held in a 

 non-oxidizing flame. The mean of several observations shows 

 that the mercury is taken up in the proportion of eleven parts to 

 seven parts of zinc. The difference between the extremes from 

 which this mean is taken is *025 in eleven parts mercury. The 

 proportion of zinc has been verified by analysis in the humid way. 



The following experiment will more clearly illustrate the ope- 

 ration of the test : — 



Weight of galvanized wire . . . =50 grains. 

 Weight after immersion in mercury = 46 „ 

 Weight after expelling mercury . . = 45 „ 



This will give 5 grains for the weight of zinc removed by immer- 

 sion in mercury. 



Weight of mercury taken up by alloy = 1 grain, 



which will represent 0*46 grain of zinc combined with the iron. 

 Consequently 50 grains galvanized iron wire contains 5*46 grains 

 zinc, of which only 0'46 is in chemical combination. 



In all the specimens examined, the irregularity in the thickness 

 of the zinc was so great that no reliance can be attached to its 

 estimated value. 



Tamworth House, 

 Mitcham Common. 



