Here's the passage I think you have in mind from ch. 18:

The rest of the evening brought her little amusement. She was teased by Mr. Collins, who continued most perseveringly by her side, and though he could not prevail with her to dance with him again, put it out of her power to dance with others. In vain did she entreat him to stand up with somebody else, and offer to introduce him to any young lady in the room. He assured her that, as to dancing, he was perfectly indifferent to it; that his chief object was, by delicate attentions, to recommend himself to her, and that he should therefore make a point of remaining close to her the whole evening. There was no arguing upon such a project. She owed her greatest relief to her friend Miss Lucas, who often joined them, and good-naturedly engaged Mr. Collins's conversation to herself.