With the Heart of Darkness example, I provide the preceding and following sentence of the longest sentence in the book as it frames the longest sentence very nicely. In order to make clear which sentence is the longest I have presented it in a boldface.
Without further ado... Here are the longest sentences in Alice in Wonderland and Heart of Darkness.
Alice in Wonderland
Hardly knowing what she did, she picked up a little bit of stick, and held it out to the puppy; whereupon the puppy jumped into the air off all its feet at once, with a yelp of delight,and rushed at the stick, and made believe to worry it; then Alice dodged behind a great thistle, to keep herself from being run over; and the moment she appeared on the other side, the puppy made another rush at the stick, and tumbled head over heels in its hurry to get hold of it; then Alice, thinking it was very like having a game of play with a cart-horse, and expecting every moment to be trampled under its feet, ran round the thistle again; then the puppy began a series of short charges at the stick, running a very little way forwards each time and a long way back, and barking hoarsely all the while, till at last it sat down a good way off, panting, with its tongue hanging out of its mouth, and its great eyes half shut.
How could you?--with solid pavement under your feet, surrounded by kind neighbours ready to cheer you or to fall on you, stepping delicately between the butcher and the policeman, in the holy terror of scandal and gallows and lunatic asylums--how can you imagine what particular region of the first ages a man's untrammelled feet may take him into by the way of solitude--utter solitude without a policeman--by the way of silence--utter silence, where no warning voice of a kind neighbour can be heard whispering of public opinion? These little things make all the great difference.
later...