without added sodium hydroxide?
Answer. Paraformaldehyde is a white solid formed by combination of large numbers of formaldehyde molecules in an aqueous solution: a polymer. Formaldehyde, HCHO, is a gas and strictly speaking it doesn’t exist in aqueous solution because it tacks on a water molecule to form methylene hydrate, which is HO-CH2-OH. This is the active ingredient of fixatives. Methylene hydrate molecules just love one another, and join together (eliminating H2O, so I suppose it’s really the original formaldehyde carbon atoms that are so affectionate) to make polymers of all sizes. In commercial formalin (37-40% HCHO by weight) the polymer molecules are small enough to stay in solution. In paraformaldehyde they are big enough to be insoluble. Manufacturers add some methanol to formalin. This retards the formation of large polymer molecules (see Recommended Reading if you want to know why). Probably the methanol doesn’t affect fixative properties when diluted, though some people in the late 1950s claimed that
Answer. Paraformaldehyde is a white solid formed by combination of large numbers of formaldehyde molecules in an aqueous solution: a polymer. Formaldehyde, HCHO, is a gas and strictly speaking it doesn’t exist in aqueous solution because it tacks on a water molecule to form methylene hydrate, which is HO-CH2-OH. This is the active ingredient of fixatives. Methylene hydrate molecules just love one another, and join together (eliminating H2O, so I suppose it’s really the original formaldehyde carbon atoms that are so affectionate) to make polymers of all sizes. In commercial formalin (37-40% HCHO by weight) the polymer molecules are small enough to stay in solution. In paraformaldehyde they are big enough to be insoluble. Manufacturers add some methanol to formalin. This retards the formation of large polymer molecules (see Recommended Reading if you want to know why). Probably the methanol doesn’t affect fixative properties when diluted, though some people in the late 1950s claimed that
