﻿132 Mr. T. T. P. B. Warren on the Estimation 



The price of the complete apparatus, with the improvements 

 above described, and packed in an elegant case, is 240 Bavarian 

 florins, which are equal to £20. 



I am, Sir, 



Yours respectfully, 



Stgmund Merz. 



XX. Estimation of Zinc on Galvanised Iron. 

 By Thomas T. P. Bruce Warren*. 



MANUFACTURED articles of iron, when coated with zinc, 

 are said to be " galvanized." The word galvanized was 

 probably suggested by the fact that iron covered with zinc was, 

 in its earlier introduction, produced by means of galvanic action. 



Iron in the form of wire is galvanized by drawing through a 

 bath of molten zinc, and in other forms (as sheets &c.) by simple 

 immersion or dipping. The surface of the iron being rendered 

 chemically clean immediately before coming into contact with the 

 zinc, a portion of the zinc combines with the iron at its surface 

 and forms a thin layer of alloy, to which a further quantity of 

 zinc readily adheres. The alloy of iron and zinc, when freed 

 from the uncombined zinc, is capable of taking up a definite 

 quantity of mercury, which, when carefully heated, is again given 

 off without any apparent alteration in the alloy. 



The following process, which is based upon these considera- 

 tions, is recommended more especially to the notice of telegraph 

 engineers for estimating quantitatively the amount of zinc on 

 galvanized iron wires. 



The wire when weighed is carefully cleaned with dilute sul- 

 phuric acid and immersed in mercury for a few hours, or until 

 all the zinc which is capable of being dissolved is removed. The 

 crystalline amalgam, which after a short time forms on its sur- 

 face, should be wiped off and the wire left undisturbed at the 

 bottom of the mercury for four or eight hours. 



The adhering particles of mercury being removed, the wire is 

 well rubbed with a chamois leather and weighed. The lossf will 

 not only show the extra quantity of zinc on the wire beyond what 

 is actually required for producing a chemically galvanized sur- 

 face, but will expose those parts of the wire to which the zinc has 

 not combined and which would in a short time scale off. The 

 wire, if properly galvanized, should be uniformly coated with 

 amalgam, and present a bright silvery appearance when rubbed. 



This wire is now heated so as to expel the mercury, and again 



* Communicated by the Author. 



t To this must be added the weight of mercury retained by the alloy. 



