Health Canada recently issued an advisory about minimizing exposure to borax based on some studies that have found developmental and reproductive problems in animals. This raised questions among teachers who use the reaction of borax with polyvinyl alcohol to form “slime,” demonstrating the ability of boron compounds to cross-link polymers. In response to queries about the use of borax in this fashion, Health Canada has clarified its warning saying that “the main concern with the use of boron-containing substances for making slime or putties, is with accidental or intentional ingestion." There is no issue if students are properly supervised to prevent ingestion. In all my years of demonstrating the "slime" reaction in front of thousands of students, I have never had one ask if they could taste the slime.
Another concern has been raised about the use of borax prompted by an account of chemical burns suffered by a student who was playing with slime. Borax is a strong base and can certainly harm the skin but this kind of a chemical burn is most unusual. It is not clear whether something else may have been involved as well. In any case, due to the attention being garnered by borax, I thought it would be interesting to delve a bit more deeply into this interesting chemical. Here we go.
One day a craftsman showed up in the court of Tiberius, Emperor of Rome (14AD to 37AD), to present the ruler with a beautiful transparent glass vase. Just as he was about to hand it to Tiberius, the man let the vessel slip through his fingers. Everyone jumped, expecting a crash and flying glass. Roman glass, after all, had a history of fragility. But the glass did not break! Tiberius was very impressed and asked the glassmaker for the secret of the unbreakable vase. The craftsman was unwilling to divulge his method and boasted that he alone would be the keeper of the secret. This did not sit well with the ruthless Emperor who had the glassmaker put to death.
The unfortunate artisan had probably stumbled on a method of making borosilicate glass. Ordinary glass is made by heating together sand, limestone and sodium oxide, a process that was well known to the Ancient Romans. If certain boron compounds are added to the mix, the glass becomes shatter resistant. This is the kind of glass we regularly use today in laboratories.
Sodium borate, or borax, as it is better known, was used by Roman goldsmiths as a "flux," a substance added to the metal to make it flow more easily when heated. We can only hypothesize that the glassmaker added some borax to his molten mix to improve its flow properties and noted that the resulting glass was much stronger. The Romans never did discover the secret and it was only in 1916 that an American patent officially described shatterproof "Pyrex" glass which contained a high percentage of boric oxide. Pyrex can withstand extreme temperature changes without cracking and is ideal for ovenware.
Borax was a rarity in ancient Rome, found only around some hot springs in Tuscany. But then in the 13th century, Marco Polo returned from the Orient with samples of gunpowder, spaghetti and white crystals of borax. The Italians immediately figured out that they could make spaghetti themselves, but the borax had to be imported. Caravans were organized and soon Venetian goldsmiths were blessed with an ample supply of this ideal welding flux.
Europeans also learned that the Chinese used borax in pottery glazes and began trying it themselves for this purpose. Addition of borax to improve the flow qualities of molten glass was a natural extension of this process. But the substance was still hard to come by. The "age of borax" did not begin until 1870 when huge natural deposits were found in the Nevada desert. It was there for the taking, all that was needed was a shovel.
Soon prospectors were crawling all over the desert to search for the best deposits of the mineral. The borax rush was on! Since the mineral cannot be readily recognized just by appearance, some simple identification test was needed. Prospectors discovered that if sulfuric acid and alcohol were poured on a suspect ore, and the mix ignited, a green flame signified the presence of borax.
Sulfuric acid reacts with sodium borate to form boric acid, which is readily consumed in the flame generated by the burning alcohol. A green "flame test," characteristic of boron is still used today to identify the element. It was just such a flame that prompted grizzled prospector Aaron Winters to let out a scream which brought his wife running in 1881. "She burns green Rosie! We're rich!"
Indeed the find in Death Valley was a major one, and Winters was paid the staggering amount of $20,000 for his claim by developer William T. Coleman. But there was a problem. How could the huge amounts of borax be moved out of the desert without a railroad link? The inventive Coleman came up with the idea of gigantic wagons drawn by a "20 mule team." Fully loaded, they weighed 32,000 pounds each and had wheels seven feet high!
The 20 day round trip through the desert to Mojave, the nearest railroad junction, was treacherous, with temperatures often exceeding 45oC. Nevertheless, in six years 20 million pounds of borax were moved out by the 20 mule teams. This was more borax than the world needed and Coleman eventually went bankrupt.
It was at this point that F.M. "Borax" Smith entered the picture and resuscitated the company with his imaginative ideas. He was going to make borax a household staple! Soon advertisements hyped the product as a complexion aid, a milk preservative, a cure for epilepsy and bunions and an additive for bath water and carriage washes. The latter claim proved to be sound, borax binds minerals which can interfere with the cleaning action of soaps and detergents. Indeed, borax is widely used in laundry products to this day. If you want to improve the appearance of your laundry, and cut down on detergent use, just add about a third of a cup of borax to each load. A quarter cup of borax dissolved in two cups of water is also a great spot remover for carpets!
Most of the world supply of borax now comes from a gigantic open pit mine in California near a town that has been appropriately named Boron. There are now a myriad uses for the material which started its technological life as a gold flux. It is used to make glass for car headlights, enamel for stoves and refrigerators, ceramic tiles, antiseptics, bleach for unbleachables, weed killers and fertilizers. Thin fibers made from elemental boron are used to reinforce resins destined for aircraft and space vehicle parts.
Boric acid, which is made from borax, can be used to control cockroaches. A bait made with flour and sugar and spiced with boric acid is likely to be their last supper. Even if they choose not to dine, the crystals of boric acid stick to the exoskeleton and rub away the oily protective layer. The creatures dehydrate and die. Ants suffer a similar fate.
Finally, borax can even teach us some neat chemistry. Just combine half a tablespoon of it with half a cup of white glue and stir! Almost miraculously the sticky glue changes into a putty which can be stretched or rolled into a ball. What happened? The glue is made of long molecules of polyvinyl acetate which easily slip and slide past each other. Borax links these long molecules together, forming a semi-rigid three-dimensional network of molecules which is neither a liquid nor a solid. But it is a lot of fun. Tiberius would have loved it. Just make sure nobody eats it.
