these disadvantages is
the phosphate process invented by Thomas Watts Coslett, an English
chemist, in 1907, and developed in America by the Parker Company of
Detroit. This consists simply in dipping the sheet iron or articles into
a tank filled with a dilute solution of iron phosphate heated nearly to
the boiling point by steam pipes. Bubbles of hydrogen stream off rapidly
at first, then slower, and at the end of half an hour or longer the
action ceases, and the process is complete. What has happened is that
the iron has been converted into a basic iron phosphate to a depth
depending upon the density of articles processed. Any one who has
studied elementary qualitative analysis will remember that when he added
ammonia to his "unknown" solution, iron and phosphoric acid, if present,
were precipitated together, or in other words, iron phosphate is
insoluble except in acids. Therefore a superficial film of such
phosphate will protect the iron underneath except from acids. This film
is not a coating added on the outside like paint and enamel or tin and
nickel plate. It is therefore not apt to scale off and it does not
increase the size of the article. No high heat is required as in the
Sherardizing and Bower-Barff processes, so steel tools can be treated
without losing their temper or edge.

The deposit consisting of ferrous and ferric phosphates mixed with black
iron oxide may be varied in composition, texture and color. It is
ordinarily a dull gray and oiling gives a soft mat black more in
accordance with modern taste than the shiny nickel plating that
delighted our fathers. Even the military nowadays show more quiet taste
than formerly and have abandoned their glittering accoutrements.

The phosphate bath is not expensive and can be used continuously for
months by adding more of the concentrated solution to keep up the
strength and removing the sludge that is precipitated. Besides the iron
the solution contains the phosphates of other metals such as calcium or
strontium, manganese, molybdenum, or tungsten, according to the
particular purpose. Since the phosphating solution does not act on
nickel it may be used on articles that have been partly nickel-plated so
there may be produced, for instance, a bright raised design against a
dull black background. Then, too, the surface left by the Parker process
is finely etched so it affords a good attachment for paint or enamel if
further protection is needed. Even if the enamel