Here is the passage in chapter 22 that contains sexual content:
Here is the screenshot from chapter 25:
Note: If you are interested in this book and are feeling like skipping it due to the above, perhaps you can consider doing it as a read-aloud or skipping that chapter, instead. The book is rated #4, so it’s the lowest on the priority list. If you don’t feel comfortable with it, it can be easily skipped, or you can choose the option #2 book: The Radium Girls: Young Readers’ Edition: The Scary but True Story of the Poison that Made People Glow in the Dark.
Having said that, the Uncle Tungsten book is wonderfully written biography full of history and the story of a boy falling in love with science (plus tons of scientific facts sprinkled about in a way that is a joy to read).