The Slum works as reference material in an essay when the theme is inequality, housing or cultural identity, as long as you cite the book's fact (who does what and in which chapter) and only then connect it to the theme. Three angles where it works, each with the fact that supports it:
Ambition and the labor of others. João Romão gets rich by keeping Bertoleza's savings, raising the little houses with stolen stone and calculating, when he hires the quarryman, that "my seventy milreis will come back to my drawer". The book ends with him receiving a diploma of honorary member at the very moment Bertoleza dies. It serves to show how one person's success can rest on the work of others and be honored without anyone looking at the cost.
Popular housing and the city. The tenement fills up until "the cocoons split into cubicles the size of graves", and yellow fever kills two residents. After the rebuilding, São Romão Avenue raises its prices and begins to require, "to enter", "a letter of surety and a special recommendation", and many of the old lodgers leave for Cabeça-de-Gato. It serves to speak about housing, public health and who is left out when a place improves.
Cultural mixing and the immigrant's adaptation. Jerônimo arrives from Portugal thrifty and serious and, in Rio, "cane brandy replaced wine", coffee and black beans enter the house, and the Bahian chorado silences the fado. The rivalry between Brazilians and Portuguese erupts in the fight between Piedade and Rita, but in the fire "there were no longer Brazilians and Portuguese there, there was only one party". It serves to speak about immigration, identity and coexistence between different origins.
Caution: use the book for what it shows, not for theses it does not put forward. The narrator does not preach, and slavery appears as plot and period, in the false letter and in Bertoleza's return.