Complex sentence: If the solution is made rapidly the solution will instantly boil, giving off large amounts of corrosive fumes, even when made with care the resultant heat can bring solution temperatures exceeding 100 ° C. It must be allowed to cool reasonably before it is used.
Split into simpler sentences: If the solution is made rapidly, it will instantly boil, releasing large amounts of corrosive fumes. Even when made with care, the resultant heat can bring solution temperatures above 100 ° C. It must be allowed to cool reasonably before it is used.