In combination, what do the two documents tell about the goals, desires, and complaints of industrial men in the second half of the 19th...

Before the industrial revolution most people were farmers
or owned/ were employed by small local buisnesses.  The industrial revolution allowed
large corporations and eventually monopolies to start holding great power.  People had
little choice but to accept the jobs and conditions they were offered.  The government
had very few laws regulating workplaces during this time.  If an employer said you must
work 12 hours without a break workers had no choice but to accept the work or lose their
only available income.  The factory down the street would not offer conditions that were
any better.  There was no minimum wage so buisnesses could pay as little as they
wanted.  Since all wages were low and many workers were available market forces kept pay
very low.  Children were forced to work to help their parents support their families. 
Horrible conditions existed as evidenced in photographs such as those of Lewis Hine (see
the link in the reference section).  Many workers died in mine and factory accidents
such as the fire at the Triangle Shirtwaist Factory in New York City.  In the "Plea for
eight hours"  the author explains that market forces keep pay artificially low and that
the government should step in to help workers gain better conditions.  The author
explains that workers are unable to improve these conditions individually.  In the
second article "The Knights of Labor"  (I assume you mean the "Preamble and Platform of
the Knights of Labor")  the same ideas are laid out.  The platform explains the need for
an end to child labor, fair pay for men and women, laws providing for health and safety
of workers.