Early chemistry sets included a wide range of hardware, glassware and chemicals, much of which is omitted from modern-day sets due to later concerns about possible hazards and liability. Modern chemistry kits tend to discourage free-form experimentation, containing a limited amount of specific nontoxic substances and a booklet specifying how they can be used for a specific project. Writers frequently lament that it is no longer possible for chemistry-set users to engage in the wide range of (sometimes hazardous) experimentation that attracted them to the field of chemistry as children.