GALVANISED IRON 



533 



liging in silky needles of tho greatest whiteness ; soluble in about 100 times its weight 

 of cold, and in a much smaller quantity of boiling water ; more soluble in alcohol 

 than in water, but little so in sulphuric ether. 



Gallic acid does not dissolve the salts of protoxide of iron, but it forms, with the 

 sulphate of the peroxide, a dark blue precipitate, much less insoluble than the tannutQ 

 of iron. 



Imports. 



GALMEI. German mineralogists usually recognise the silicate of zinc (Smith- 

 sonite) under this name. See ZINC. 



GA1VATJISE33 IRON. This is the name, improperly given, first in France and 

 subsequently adopted in this country, to iron coated with zinc by a peculiar patent 



In 1837 Mr. H. W. Crawfurd patented a process for zincing iron. In the 'Ee- 

 pertory of Patent Inventions ' his process is thus described : Sheet iron, iron castings, 

 and various other objects in iron are cleaned and scoured by immersion in a bath of 

 water, acidulated with siilphuric acid, heated in a leaden vessel, or used cold in one 

 of wood, just to remove the oxide. They are then thrown into cold water, and taken 

 out one at a time to be scoured with sand and water with a piece of cork, or more 

 usually with a piece of the husk of the cocoa-nut, the ends of the fibres of which serve 

 as a brush, and the plates are afterwards thrown into cold water. 



Pure zinc covered with a thick layer of sal-ammoniac is then melted in a bath, and 

 the iron, if in sheets, is dipped several sheets at a time in a cradle or grating. The 

 sheets are slowly raised to allow the superfluous zinc to drain off, and are thrown 

 whilst hot into cold water, on removal from which they only require to be wiped dry. 



Thick pieces are heated, before immersion, in a reverberatory furnace, to avoid 

 cooling the zinc. Chains are similarly treated, and on removal from the zinc require 

 to be shaken until cold to avoid the links being soldered together. Nails and small 

 articles are dipped in muriatic acid, and dried in a reverberatory furnace, and then 

 thrown altogether in the zinc, covered with the sal-ammoniac, left for one minute, and 

 taken out slowly with an iron skimmer ; they come out in a mass soldered together, 

 and for their separation are afterwards placed in a crucible and surrounded with 

 charcoal-powder, then heated to redness and shaken about until cold for their separa- 

 tion. Wire is reeled through the zinc, into which it is compelled to dip by a fork or 

 other contrivance. It will be understood that the zinc is melted with a thick coat of 

 sal-ammoniac to prevent the loss of zinc by oxidation. 



Mr. Mallet coated iron with zinc by the following process : 



The plates are immersed in a cleansing bath of equal parts of sulphuric or muriatic 

 acid and water, used warm ; the works are then hammered and scrubbed with emery 

 and sand to detach the scales, and to thoroughly clean them ; they are then immersed 

 in a ' preparing bath ' of equal parts of saturated solutions of muriate of zinc and sal- 

 ammoniac, from which the works are transferred to a fluid metallic bath, consisting of 

 202 parts of mercury and 1292 parts of zinc, both by weight, to every ton weight of 

 which alloy is added above one pound of either potassium or sodium, the latter being 

 preferred. As soon as the cleaned iron-works have attained the melting heat of the 

 triple alloy, they are removed, having become thoroughly coated with zinc. At the 

 proper fusing temperature of this alloy, which is about 680 Fahr., it will dissolve a 

 plate of wrought iron of an eighth of an inch thick in a few seconds. 



Morewood and Eogers's galvanised tinned iron is prepared under several patents. 

 Their process is as follows : 



The sheets are pickled, scoured, and cleaned, just the same as for ordinary tinning. 

 A large wooden bath is then half filled with a dilute solution of muriate of tin, pre- 

 pared by dissolving metallic tin in concentrated muriatic acid, which requires a period 



