It's been around since ancient Egypt, and for most of that time, working with hide glue meant mixing it yourself and heating it all day to keep it liquified. But since the 1930s, we've had the option of using bottled hide glue that stays liquid at room temperature. Liquid hide glue offers several other advantages for beginner and veteran alike, helping to reduce the stress of assembly and finishing while matching more modern glues for strength.

From Fine Woodworking #228