Comment about Formaldehyde and Formalin
solution is percent WEIGHT IN WEIGHT
Formaldehyde is a GAS which is available as a stock solution called "Formaldehyde Solution BP 1988" which contains 34 - 38 % w/w Formaldehyde (giving an average of 36 % w/w).
Formaldehyde Solution BP 1988 is also known as Formalin.
Formaldehyde Solution BP = Formalin