92 REPORT—1843. 
357. The iron, cleansed by the previous operations, is immersed in this 
solution, contained in vessels of wood or pottery, or stone, at common tem- 
peratures ; as soon as the surfaces of the cleansed iron appear covered all over 
with minute bubbles of gas, it is in a fit state to be submitted to the final 
operation of immersing in the metallic alloy with which it is to be coated ; 
but the iron, when once cleansed, may be permitted to remain in the “ pre- 
paring bath” for any moderate length of time, without injury to the subse- 
quent process. The “preparing bath” becomes therefore a convenient re- 
ceptacle for depositing and preserving the cleaned or polished iron in until 
ready for coating with the alloy. 
358. The next part of the process consists in covering the iron with the 
preservative alloy, which is to be prepared in the following manner :—Zine 
is to be melted in a suitable vessel, which is best of pottery or stone; and 
when in fusion mercury is to be added to it, in the proportion of 202 parts 
of mercury to 1292 parts of zinc, both by weight; that is, 40 atoms of zinc 
to 1 of mercury, or thereabouts. These are to be well stirred or mixed to- 
gether with a rod of dry wood, or of iron coated with clay. To the above 
alloy is now to be added either potassium or sodium, in the proportion of one 
pound to every ton weight; the alloy of either will answer the purpose, 
but I prefer sodium, as more easily obtained and more manageable. These 
metals are usually preserved from oxidation in naphtha, or some other fluid 
not containing oxygen. They are to be removed from this in small portions, 
not more than half an ounce at a time, placed in a small inverted cup of 
wood formed on the end of a stick and thrust rapidly below the surface of 
the alloy of zine and mercury, with which either may be made thus to com- 
bine easily, and without loss or combustion of the alkaline metal. The triple 
alloy thus formed of zinc, mercury and sodium, or potassium, after having 
been again stirred and mixed with the dry wood rod, is ready for coating the 
prepared iron when immersed in it. The combination of these metals is faci- 
litated, and their oxidation on the surface retarded, by strewing upon it some of 
the salts contained in solution in the “ preparing bath” when in a dry state. 
359. The plates of iron or other articles are now to be taken up out of the 
“ preparing bath,” permitted to drain for a few seconds, and immediately, 
while still wet with the liquor, immersed in the fused alloy ; and as soon as 
they have acquired its temperature, which should not be raised higher than is 
necessary for fusion, they are to be withdrawn again edgewise, and will be found 
covered with a perfectly uniform and coherent coat or surface of the alloy. 
360. The affinity of this alloy for iron is so intense, and the peculiar cir- 
cumstances of surface induced by the preparing bath upon the iron presented 
to it are such, that care is requisite, lest, by too long an immersion, the plates 
or articles of iron should be partially dissolved ; and where the articles to be 
covered are small, or their parts minute, it is necessary, before immersing 
them, to permit the alloy to dissolve or combine with some wrought iron, in 
order that its affinity for iron may be partially satisfied, and so this risk be 
avoided. The alloy will, at its proper fusing temperature, which is about 
680° Fahr., dissolve a plate of wrought iron of an eighth of an inch thick in 
a few seconds, and form with it a quadruple alloy. 
More or less mercury and more or less of the alkaline metals may be used 
in forming this alloy, but the proportions given are those I have found best, 
as the alloy is permanent at its temperature of fusion; 7.e. no mercury is 
lost by volatilization, nor does the alloy show any inconvenient tendency to 
oxidation, much less indeed than common zinc does at the surface, which is 
in the case of the alloy to remain covered with any oxide produced, and with 
the dry salt, the double chloride of the preparing bath transferred to it on 
