Both urea formaldehyde and phenol formaldehyde are carcinogenic in very high concentrations. Hexamethylenetetramine forms readily from aqueous ammonia and formaldehyde. These compounds include methanol, methyl amines, formaldehyde, and formate. Dioxolane is formed by reaction of ethylene glycol with aqueous formaldehyde over an acid catalyst. Novolaks are produced by reacting phenol with methanal (formaldehyde). Smaller aldehydes are more soluble in water, formaldehyde and acetaldehyde completely so. It is prepared industrially by combining formaldehyde and ammonia. Baekeland began to investigate the reactions of phenol and formaldehyde. Hexamine is prepared by the reaction of formaldehyde and ammonia. It is produced from urea and formaldehyde. Early stages in the reaction of formaldehyde and urea produce bis(hydroxymethyl)urea. Several preservatives are available, including thiomersal, phenoxyethanol, and formaldehyde. It used sulfamic acid, formaldehyde, and nitric acid. The hydroxymethanesulfinate ion is unstable in solution towards decomposition to formaldehyde and sulfite. Also applicable for accelerated curing of low formaldehyde adhesives.