I have a couple of questions about common B&W chemicals....

What is residual hydroquinone and how is it different from hydroquinone? Can either be used to make developers? Are there any conversion necessary if a recipe calls for hydroquinone and I use "residual" type?

Why is ammonium thiosulfate only available in 60% solution rather than powder?? For example, a recipe in "Way Beyond" book calls for 120 grams of ammonium thiosulfate. It does not say in what hydration. (anhydrous/monohydrate/etc) Many other recipe I've seen is the same way. Is this a convention that I'm not aware of?

Can someone give me a hand?