in formic acid fuel cells and indirectly in hydrogen fuel cells). electrolytic conversion of electrical energy to chemical fuel has been proposed as a large-scale source of formate by various groups. the formate could be used as feed to modified e. coli bacteria for producing biomass. natural microbes do exist that can feed on formic acid or formate (see methylotroph). formic acid has been considered as a means of hydrogen storage. the co-product of this decomposition, carbon dioxide, can be rehydrogenated back to formic acid in a second step. formic acid contains 53 g/l hydrogen at room temperature and atmospheric pressure, which is three and a half times as much as compressed hydrogen gas can attain at 350 bar pressure (14.7 g/l). pure formic acid is a liquid with a flash point of +69 °c, much higher than that of gasoline (−40 °c) or ethanol (+13 °c). it is possible to use formic acid as an intermediary to produce isobutanol from co2 using microbes. soldering formic acid has a potential application in soldering. due to its capacity to reduce oxide layers, formic acid gas can be blasted at an oxide surface in order to increase solder wettability. chromatography formic acid used as a volatile ph modifier in hplc and capillary electrophoresis. formic acid is often used as a component of mobile phase in reversed-phase high-performance liquid chromatography (rp-hplc) analysis and separation techniques for the separation of hydrophobic macromolecules, such as peptides, proteins and more complex structures including intact viruses. especially when paired with mass spectrometry detection, formic acid offers several advantages over the more traditionally used phosphoric acid. other uses formic acid is also significantly used in the production of leather, including tanning (23% of the global consumption in 2009), and in dyeing and finishing textiles (9% of the global consumption in 2009) because of its acidic nature. use as a coagulant in the production of rubber consumed 6% of the global production in 2009. formic acid is also used in place of mineral acids for various cleaning products, such as limescale remover and toilet bowl cleaner. some formate esters are artificial flavorings and perfumes. formic acid application has been reported to be an effective treatment for warts. safety formic acid has low toxicity (hence its use as a food additive), with an ld50 of 1.8 g/kg (tested orally on mice). the concentrated acid is corrosive to the skin. formic acid is readily metabolized and eliminated by the body. nonetheless, it has specific toxic effects; the formic acid and formaldehyde produced as metabolites of methanol are responsible for the optic nerve damage, causing blindness, seen in methanol poisoning. some chronic effects of formic acid exposure have been documented. some experiments on bacterial species have demonstrated it to be a mutagen. chronic exposure in humans may cause kidney damage. another possible effect of chronic exposure is development of a skin allergy that manifests upon re-exposure to the chemical. concentrated formic acid slowly decomposes to carbon monoxide and water, leading to pressure buildup in the containing vessel. for this reason, 98% formic acid is shipped in plastic bottles with self-venting caps. the hazards of solutions of formic acid depend on the concentration. the following table lists the globally harmonized system of classification and labelling of chemicals for formic acid solutions: concentration (weight percent) pictogram h-phrases 2–10% h315 10–90% h313 >90% h314 formic acid in 85% concentration is flammable, and diluted formic acid is on the u.s. food and drug administration list of food additives. the principal danger from formic acid is from skin or eye contact with the concentrated liquid or vapors. the u.s. osha permissible exposure level (pel) of formic acid vapor in the work environment is 5 parts per million parts of air (ppm).