Alchemy skills represent the ability to manipulate base ingredients into functional potions. These potions can be applied by an alchemist or specially prepared to be applied by anyone. Alchemists may be full-time researchers and traders, or may be part-time alchemists who use their alchemy skills to compliment their other abilities.
Skills followed by a number or range of numbers indicate a levelled skill, this skill has multiple levels, with higher levels having different effects. To purchase a levelled skill you must have the previous levels (e.g. to purchase first aid 3 to treat somebody you must have first aid 1 and 2) in addition to any other pre-requites. The XP cost represents the XP cost per level.
Skills without a number are non-levelled: there is no progression for them, you buy them only once unless specified in the skills description.
You must be level N to buy any level N skills - for example, at chargen, your character is level 3, you may purchase skills up to level 3, but must wait until you reach level 4 (181XP) before you can buy level 4 skills.