Potassium nitrate (niter or saltpeter), sodium chloride, sodium borate (borax), and boric acid are employed as food preservatives, as in corned beef, ham, butter, etc. Wiley says that the small quantities of salt in butter are not preservative.

Boric acid, a crystalline solid, is soluble in 18 parts of water, 16 of alcohol, and 5 of glycerin, and volatilizes when its solution is boiled. It is soothing locally, and mildly antiseptic. Post and Nicoll (1907) obtained no essential germicidal effect in twenty hours from saturated aqueous solutions; but Bernstein (1910) has demonstrated that it has some power to check the growth of yeasts and harmless saprophytes, though only slight effect on typhoid and other pathogenic germs. It is more effective, therefore, as a preservative than as a disinfectant. About the body it possibly acts more by changing the reaction of the fluids than by directly retarding the microbic growths.

Its solution is used extensively as a cleansing application to inflamed mucous membranes, as of the eye, nose, mouth, vagina, etc.; its ointment, as an application to eczematous areas, fungous skin diseases, and burns; and the acid itself as a dusting-powder in the shoes in sweating of the feet. It is almost specific against thrush in the mouths of infants. With salicylic acid it forms the antiseptic wash "boro-sal" or Thiersch's solution, which consists of boric acid, 8; salicylic acid, 2; and water, to make 1000. For children it has a wide range of application. Boric acid and its alkaline salt, sodium borate or borax, are very widely employed as food preservatives. Borax was recommended by Gowers in epilepsy in doses of 20 grains (1.3 gm.) three times a day.

Toxicology

Boric acid has been the cause of a number of cases of poisoning, the symptoms being: gastro-enteritis with vomiting and diarrhea, a papular eruption on the skin, general edema, a gray line on the gums, and central depression leading to collapse. Best (1904) gathered from the literature 5 cases of severe poisoning and 5 deaths. Severe symptoms have resulted from irrigating the colon with boric-acid solution, from packing the vagina, the ankle-joint, etc., with the powder, from washing out the pleural cavity, a lumbar abscess, etc. Recovery is reported of an infant of eight weeks after 2 doses of 3 ounces (90 c.c.) of a saturated solution, part of which was vomited. The treatment is abundance of water and alkalies.

The glycerite of boroglycerin, a thick liquid made of boric acid and glycerin, is used on vaginal tampons in chronic endometritis and pelvic inflammations.