I'm a little confused by the pure groups presented in Chapter 2 of RTKII.

At first, I assumed this chapter was providing the-one-and-only On-yomi for those characters presented. So for 工　the on-yomi would always be こう and for 白 it would be はく。But then of course there is く　for 工 and ビャク for 白. So then I figured what was meant in was simply that the pure groups in Chapter 2 shared ONE on-yomi (but there could be others). But this quote from Chapter 2--". . . each time you see this primitive element, you can be sure what the Chinese reading will be." But of course, if there are 2 on-yomi, then you can't really be sure. Can anyone get me back on track here? Thanks in advance.

I share the same confusion about some of those discrepancies, sorry I can't help. But I am just ignoring his descriptions and going through it with the motto that "ALMOST ALL of the time this will be read as X" which in my opinion is EXTREMELY useful and has already sky-rocketed my reading ability. There are many exceptions about when it's Chinese vs. Japanese reading anyway, so there's no need to think of hard and fast rules for groups of readings either. It's just helpful to have them grouped like this to see some of the patterns that are there. However, if someone actually knows the correct interpretation of his words, it would be great to hear. Meanwhile, I just take it with a grain of salt, just like Volume I.

It means exactly that. All kanji with the 工 primitive will be read as コウ. 功 巧 江 扛 攻 杠 杠 肛 矼 紅 虹 缸 貢 訌 控 腔 項 椌 槓 熕 箜 all have コウ as their (main) 音読み.

工 as a standalone kanji, however, has other readings. The same goes for 白.

At least, that's how I see it. tuuli does have a strong point in saying there are no hard rules, however. Always take it with a grain of salt when Heisig says something is always this or always that.

Thanks for the input.