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Borax crystals
Ball-and-stick model of the unit cell of borax decahydrate
IUPAC name
Sodium tetraborate decahydrate
Other names
Borax decahydrate
3D model (JSmol)
ECHA InfoCard 100.014.129
EC Number 215-540-4
E number E285 (preservatives)
Na2B4O7·10H2O or Na2[B4O5(OH)4]·8H2O
Molar mass 381.38 (decahydrate)
201.22 (anhydrate)
Appearance white solid
Density 1.73 g/cm3 (decahydrate, solid)[1]
2.4 g/cm3 (anhydrate, solid)[1]
Melting point 743 °C (1,369 °F; 1,016 K) (anhydrate)[1]
75 °C (decahydrate, decomposes)[1]
Boiling point 1,575 °C (2,867 °F; 1,848 K) (anhydrate)[1]
−85.0·10-6 cm3/mol
Monoclinic Prismatic
S01AX07 (WHO)
GHS pictograms The health hazard pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)
P201, P308+313
NFPA 704
US health exposure limits (NIOSH):
PEL (Permissible)
REL (Recommended)
TWA 1 mg/m3 (anhydrate and pentahydrate)[2][3]
TWA 5 mg/m3 (decahydrate)[4]
IDLH (Immediate danger)
Related compounds
Other anions
Sodium aluminate; sodium gallate
Other cations
Potassium tetraborate
Related compounds
Boric acid, sodium perborate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Borax, also known as sodium borate, sodium tetraborate, or disodium tetraborate, is an important boron compound, a mineral, and a salt of boric acid. Powdered borax is white, consisting of soft colorless crystals that dissolve in water. A number of closely related minerals or chemical compounds that differ in their crystal water content are referred to as borax, but the word is usually used to refer to the decahydrate.[1] Commercially sold borax is partially dehydrated.

Borax is a component of many detergents, cosmetics, and enamel glazes. It is used to make buffer solutions in biochemistry, as a fire retardant, as an anti-fungal compound, in the manufacture of fiberglass, as a flux in metallurgy, neutron-capture shields for radioactive sources, a texturing agent in cooking, as a precursor for other boron compounds, and along with its inverse, boric acid, is useful as an insecticide.

In artisanal gold mining, borax is sometimes used as part of a process (as a flux) meant to eliminate the need for toxic mercury in the gold extraction process, although it cannot directly replace mercury. Borax was reportedly used by gold miners in parts of the Philippines in the 1900s.[6]

Borax was first discovered in dry lake beds in Tibet and was imported via the Silk Road to the Arabian Peninsula in the 8th century AD.[7] Borax first came into common use in the late 19th century when Francis Marion Smith's Pacific Coast Borax Company began to market and popularize a large variety of applications under the 20 Mule Team Borax trademark, named for the method by which borax was originally hauled out of the California and Nevada deserts in large enough quantities to make it cheap and commonly available.[8][9]


The structure of the anion [B4O5(OH)4]2- in borax

The term borax is often used for a number of closely related minerals or chemical compounds that differ in their crystal water content:

  • anhydrous sodium tetraborate, Na2B4O7
  • sodium tetraborate pentahydrate, Na2B4O7·5H2O
  • sodium tetraborate decahydrate, Na2B4O7·10H2O

Borax is generally described as Na2B4O7·10H2O. However, it is better formulated as Na2[B4O5(OH)4]·8H2O, since borax contains the [B4O5(OH)4]2- ion. In this structure, there are two four-coordinate boron atoms (two BO4 tetrahedra) and two three-coordinate boron atoms (two BO3 triangles).

Borax is also easily converted to boric acid and other borates, which have many applications. Its reaction with hydrochloric acid to form boric acid is:

Na2B4O7·10H2O + 2 HCl -> 4 H3BO3 + 2 NaCl + 5 H2O

The "decahydrate" is sufficiently stable to find use as a primary standard for acid base titrimetry.[10]

When borax is added to a flame, it produces a yellow green color.[11] Borax is not used for this purpose in fireworks due to the overwhelming yellow color of sodium. Boric acid is used to color methanol flames a transparent green.

Borax is very soluble in ethylene glycol, moderately soluble in diethylene glycol and methanol, slightly soluble in acetone.[12] It is poorly soluble in cold water, but its solubility increases significantly with temperature.[12][13]


The English word borax is Latinized: the Middle English form was boras, from Old French boras, bourras. That may have been from medieval Latin baurach (another English spelling), borac(-/um/em), borax, along with Spanish borrax (> borraj) and Italian borrace, in the 9th century. Another name for borax is tincal, from Sanskrit.[7]

The word tincal "tinkle", or tincar "tinker", refers to crude borax, before it is purified, as mined from lake deposits in Tibet, Persia, and other parts of Asia. The word was adopted in the 17th century from Malay tingkal and from Urdu/Persian/Arabic tink?r/tank?r; thus the two forms in English. These all appear to be related to the Sanskrit nka?a.[14]

Natural sources

Borax "cottonball"

Borax occurs naturally in evaporite deposits produced by the repeated evaporation of seasonal lakes. The most commercially important deposits are found in: Turkey; Boron, California; and Searles Lake, California. Also, borax has been found at many other locations in the Southwestern United States, the Atacama desert in Chile, newly discovered deposits in Bolivia, and in Tibet and Romania. Borax can also be produced synthetically from other boron compounds.

Naturally occurring borax (known by the trade name Rasorite-46 in the United States and many other countries) is refined by a process of recrystallization.[15]

Traction steam engine hauling borax, Death Valley National Park, California, 1904


Borax-based laundry detergent

Household products

Borax is used in various household laundry and cleaning products,[16] including the "20 Mule Team Borax" laundry booster, "Boraxo" powdered hand soap, and some tooth bleaching formulas.[17]

pH buffer

Borate ions (commonly supplied as boric acid) are used in biochemical and chemical laboratories to make buffers, e.g. for polyacrylamide gel electrophoresis of DNA and RNA, such as TBE buffer (borate buffered tris-hydroxymethylaminomethonium)[18][19][20] or the newer SB buffer or BBS buffer (borate buffered saline) in coating procedures. Borate buffers (usually at pH 8) are also used as preferential equilibration solution in dimethyl pimelimidate (DMP) based crosslinking reactions.

Co-complexing agent

Borax as a source of borate has been used to take advantage of the co-complexing ability of borate with other agents in water to form complex ions with various substances. Borate and a suitable polymer bed are used to chromatograph non-glycosylated hemoglobin differentially from glycosylated hemoglobin (chiefly HbA1c), which is an indicator of long term hyperglycemia in diabetes mellitus.

Water-softening agent

Borax alone does not have a high affinity for the hardness cations, although it has been used for water-softening. Its chemical equation for water-softening is given below:

Ca2+ (aq) + Na2B4O7 (aq) -> CaB4O7 (s)? + 2 Na+ (aq)
Mg2+ (aq) + Na2B4O7 (aq) -> MgB4O7 (s)? + 2 Na+ (aq)

The sodium ions introduced do not make water 'hard'. This method is suitable for removing both temporary and permanent types of hardness.


A mixture of borax and ammonium chloride is used as a flux when welding iron and steel. It lowers the melting point of the unwanted iron oxide (scale), allowing it to run off. Borax is also used mixed with water as a flux when soldering jewelry metals such as gold or silver, where it allows the molten solder to wet the metal and flow evenly into the joint. Borax is also a good flux for "pre-tinning" tungsten with zinc -- making the tungsten soft-solderable.[21] Borax is often used as a flux for forge welding.

Small-scale gold mining

Old steam tractor and borax wagons, Death Valley National Park

Borax is replacing mercury as the preferred method for extracting gold in small-scale mining facilities. The method is called the borax method and is used in the Philippines.[22]


A rubbery polymer sometimes called Slime, Flubber, 'gluep' or 'glurch' (or erroneously called Silly Putty, which is based on silicone polymers), can be made by cross-linking polyvinyl alcohol with borax. Making flubber from polyvinyl acetate-based glues, such as Elmer's Glue, and borax is a common elementary-science demonstration.[23][24]

Food additive

Borax, given the E number E285, is used as a food additive in some countries, but is banned in some countries, like the U.S., and Thailand. As a consequence, certain foods, such as caviar, produced for sale in the US contain higher levels of salt to assist preservation.[25] Its use as a cooking ingredient is to add a firm rubbery texture to the food, or as a preservative. In Asian cooking it is mostly used for its texturing properties. In China, borax (Chinese: ; pinyin: péng sh? or Chinese: ; pinyin: yuè shí) was found to have been added to some Chinese foods like hand-pulled noodles lamian and some rice noodles like shahe fen, kway teow, and chee cheong fun recipes.[26] In Indonesia it is a common, but forbidden, additive to such foods as noodles, bakso (meatballs), and steamed rice. The country's Directorate of Consumer Protection warns of the risk of liver cancer with high consumption over a period of 5-10 years.[27]

Other uses

Rio Tinto Borax Mine Pit, Boron, California


Borax, sodium tetraborate decahydrate, according to one study, is not acutely toxic.[33] Its LD50 (median lethal dose) score is tested at 2.66 g/kg in rats,[34] meaning that a significant dose of the chemical is needed to cause severe symptoms or death. The lethal dose is not necessarily the same for humans. On pesticide information websites it is listed as a non-lethal compound and of no hazardous concerns.[35]

Borax has been in use as an insecticide in the United States with various restrictions since 1946. All restrictions were removed in February 1986 due to the low toxicity of borax, as reported in two EPA documents relating to boric acid and borax.[36][37]

EPA has determined that, because they are of low toxicity and occur naturally, boric acid and its sodium salts should be exempted from the requirement of a tolerance (maximum residue limit) for all raw agricultural commodities.[36]

Although it cited inconclusive data, a re-evaluation in 2006 by the EPA still found that "There were no signs of toxicity observed during the study and no evidence of cytotoxicity to the target organ."[38] In the reevaluation, a study of toxicity due to overexposure was checked and the findings were that "The residential handler inhalation risks due to boric acid and its sodium salts as active ingredients are not a risk concern and do not exceed the level of concern..." but that there could be some risk of irritation to children inhaling it if used as a powder for cleaning rugs.

Sodium tetraborate decahydrate has no known hazard issues.[39][clarification needed]

Conditions defined as "over-exposure" to borax dust can cause respiratory irritation, while no skin irritation is known to exist due to borax. Ingestion may cause gastrointestinal distress including nausea, persistent vomiting, abdominal pain, and diarrhea. Effects on the vascular system and human brain include headaches and lethargy, but are less frequent. "In severe poisonings, a beefy red skin rash affecting palms, soles, buttocks and scrotum has been described. With severe poisoning, erythematous and exfoliative rash, unconsciousness, respiratory depression, and renal failure."[33]

A draft risk assessment released by Health Canada in July 2016 has found that overexposure to boric acid has the potential to cause developmental and reproductive health effects. Since people are already exposed to boric acid naturally through their diets and water, Health Canada advised that exposure from other sources should be reduced as much as possible, especially for children and pregnant women. The concern is not with any one product, but rather multiple exposures from a variety of sources. With this in mind, the department also announced that registrations for certain pesticides that contain boric acid, which are commonly used in homes, will have their registrations cancelled and be phased out of the marketplace. As well, new, more protective label directions are being introduced for other boric acid pesticides that continue to be registered in Canada (for example, enclosed bait stations and spot treatments using gel formulations).[40]

Possible carcinogen

The Indonesian Directorate of Consumer Protection warns of the risk of liver cancer with high consumption of borax over a period of 5-10 years.[27]

Risk to fertility and pregnancy

Borax was added to the Substance of Very High Concern (SVHC) candidate list on 16 December 2010. The SVHC candidate list is part of the EU Regulations on the Registration, Evaluation, Authorisation and Restriction of Chemicals 2006 (REACH), and the addition was based on the revised classification of borax as toxic for reproduction category 1B under the CLP Regulations. Substances and mixtures imported into the EU which contain borax are now required to be labelled with the warnings "May damage fertility" and "May damage the unborn child".[41] It was proposed for addition to REACH Annex XIV by the ECHA on 1 July 2015.[42] If this recommendation is approved, all imports and uses of borax in the EU will have to be authorized by the ECHA.[needs update] Review of the boron toxicity (as boric acid and borates) published 2012 in Journal of Toxicology and Environmental Health concluded: "It clearly appears that human B [boron] exposures, even in the highest exposed cohorts, are too low to reach the blood (and target tissue) concentrations that would be required to exert adverse effects on reproductive functions."[43]

See also


  1. ^ a b c d e f William M. Haynes (2016). CRC Handbook of Chemistry and Physics (97th ed.). Boca Raton: CRC Press. p. 4-87. ISBN 978-1-4987-5429-3.
  2. ^ a b c "NIOSH Pocket Guide to Chemical Hazards #0057". National Institute for Occupational Safety and Health (NIOSH).
  3. ^ "NIOSH Pocket Guide to Chemical Hazards #0059". National Institute for Occupational Safety and Health (NIOSH).
  4. ^ "NIOSH Pocket Guide to Chemical Hazards #0058". National Institute for Occupational Safety and Health (NIOSH).
  5. ^ "Potential Commodities NFPA 704" (PDF). Archived from the original (PDF) on 2016-05-17. Retrieved .
  6. ^ "March 2012 ipad ewaste Filipino Borax, Pakistans Pollution, Artisanal Gold Mining". Archived from the original on 2016-10-13. Retrieved .
  7. ^ a b "Borax ( Na2B4O7. 10H2O ) - Sodium Borate - Occurrence, Discovery and Applications". 2004-08-16.
  8. ^ "American Borax Production" Scientific American September 22, 1877
  9. ^ Hildebrand, G. H. (1982) "Borax Pioneer: Francis Marion Smith." San Diego: Howell-North Books. p. 267 ISBN 0-8310-7148-6
  10. ^ Mendham, J.; Denney, R. C.; Barnes, J. D.; Thomas, M. J. K. (2000), Vogel's Quantitative Chemical Analysis (6th ed.), New York: Prentice Hall, ISBN 0-582-22628-7 p. 316.
  11. ^ Staff. "Creating Flame Colors". The Science Company. Retrieved 2008.
  12. ^ a b
  13. ^ "BORAX DECAHYDRATE (Sodium Tetraborate Decahydrate)".
  14. ^ "tincal". Oxford English Dictionary (3rd ed.). Oxford University Press. September 2005. (Subscription or UK public library membership required.)
  15. ^ Wizniak, Jaime (July 2005). "Borax, Boric Acid, and Boron - From exotic to commodity" (PDF). Indian Journal of Chemical Technology. 12 (4). ISSN 0975-0991.
  16. ^ Record in the Household Products Database of NLM
  17. ^ Hammond, C. R. (2004). The Elements, in Handbook of Chemistry and Physics 81st edition. CRC press. ISBN 978-0-8493-0485-9.
  18. ^ Peacock AC, Dingman CW. Resolution of multiple ribonucleic acid species by polyacrylamide gel electrophoresis. Biochemistry (1967) volume 6(6):1818-27.
  19. ^ Anderson S. Shotgun DNA sequencing using cloned DNase I-generated fragments. Nucleic Acids Research (1981) Volume 9(13): 3015-3027
  20. ^ Nucleic Acid Electrophoresis, D. Tietz, ed., Springer-Verlag ISBN 3-540-63959-4 (1998)
  21. ^ Dodd, J.G. (1966). "Soft soldering to tungsten wire". Am. J. Phys. 34 (10): xvi. doi:10.1119/1.1972398.
  22. ^ "The borax method" (PDF). Borax replacing mercury in small-scale mining. The Geological Survey of Denmark and Greenland (GEUS). Archived from the original (PDF) on 2008-12-06. Retrieved .
  23. ^ Parratore, Phil (1998). Wacky Science: A Cookbook for Elementary Teachers. Dubuque, IA: Kendall Hunt. p. 26. ISBN 978-0-7872-2741-8.
  24. ^ "Slime Recipe - How to Make Borax and White Glue Slime". Retrieved .
  25. ^ "Caviar glossary". The Caviar Guide a gourmet review of caviars & fish roe. Hanson Ltd, Geneva, Switzerland. Archived from the original on 2008-12-08. Retrieved .
  26. ^ "Chinese Ingredients: Borax Powder, Mushroom Extract - Chowhound". Retrieved .
  27. ^ a b "Watch Out For The Food We Consume". Directorate of Consumer Protection, Jakarta, Indonesia. 2006. Archived from the original on December 28, 2008. Retrieved .
  28. ^ "Centre for Alternative Technology". Archived from the original on 2012-08-01. Retrieved .
  29. ^ "Borax". Retrieved .
  30. ^ "Boron Basics".
  31. ^ Marie, Anne. "How To Color Fire - Fun Fireplace Instructions". Retrieved .
  32. ^ [1][dead link]
  33. ^ a b "Borax - toxicity, ecological toxicity and regulatory information". Retrieved .
  34. ^ [2][dead link]
  35. ^ "Borax - toxicity, ecological toxicity and regulatory information". Retrieved .
  36. ^ a b "Pesticide Reregistration Status | Pesticides | US EPA" (PDF). Retrieved .
  37. ^ "Pesticides | US EPA" (PDF). 2015-08-20. Retrieved .
  38. ^ "Archived copy". Archived from the original on 2015-05-03. Retrieved .
  39. ^ "Safety Data Sheet : acc. to OSHA HCS" (PDF). Retrieved .
  40. ^ "Information Update - Health Canada advises Canadians to avoid homemade craft and pesticide recipes using boric acid - Recalls & alerts - Healthy Canadians Website". 2016-07-22. Retrieved .
  41. ^ Member state committee draft support document for identification of disodium tetraborate, anhydrous as a substance of very high concern because of its CMR properties. Adopted on 9 June 2010. Retrieved on 2012-02-17.
  42. ^ Recommendation of the European Chemicals Agency of 1 July 2015 for the inclusion of substances in Annex XIV to REACH (List of Substances subject to Authorisation) Retrieved on 2015-07-06.
  43. ^ Bolt, Hermann M.; Ba?aran, Nur?en; Duydu, Yalç?n (2012). "Human Environmental and Occupational Exposures to Boric Acid: Reconciliation with Experimental Reproductive Toxicity Data". Journal of Toxicology and Environmental Health, Part A. 75 (8-10): 508-514. doi:10.1080/15287394.2012.675301. PMID 22686310.

External links

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