They were never meant to cleanse silver effects. I remember they were bugged when introduced, cleansing some silver effects (I think it was doom and maybe a few others), sometimes and only in certain situations. This was fixed and now they work as intended (I think...nobody knows with all the bugs). This means they do not work as the Alchemist's skill (which is ok I think).
One general rule that holds true in MOST cases is: IF a skill does also apply for silver (or golden) effects, it is normally written in the skill description. Something like "cleanses negative effects, including silver effects".