Formaldehyde is a gas at room temperature and one atmosphere of pressure. A saturated solution of formaldehyde in water is 37% w/w formaldehyde and this solution is properly called “formalin.” The laboratory fixative is a neutral buffered 1:10 dilution and has a formaldehyde concentration of 4% w/v. Catalog # 5754A is a 20% w/v buffered aqueous solution of formaldehyde. It is intended to be used as a concentrate that can be diluted 1 gallon with 4 gallons of reagent grade water to make the working solution. The country of origin is the United States.