Methylated spirit is actually a blend of methyl alcohol (methanol)
and ethyl alcohol (ethanol).  For any company using ethanol, 
it is a very dangerous material to use because of the danger of illicit
drinking by the staff.  To overcome this problem, ethanol is mixed with
methanol to make it taste awful.

For interest, the production of wine involves the conversion of plant
sugars (glucose and sucrose) to ethanol (ethyl alcohol).  Alcohol mixes
with water, and it is possible that hide glue joints are easier to
break after swabbing with methylated spirit because the alcohol removes
moisture from the glue.  If so, then mildly warming the glue should
reduce the absorbed moisture and achieve the same result.

For what it is worth.

Paul Rumpf,
Melbourne, Australia