Ubiquitous in many classrooms since the 19th
century, chalk and chalkboards are familiar to most of us. White, powdery and prone to
sticking to those surfaces where it is put (and just as easy to wipe away), chalk and
its accompanying board are excellent instructional aids. Notably, however, most chalk today isn’t
technically chalk at all, but gypsum. Chalk and gypsum have both been mined since
ancient times. Chalk (calcium carbonate) has been found in cave paintings that date back
to 40,000 BC, while gypsum (calcium sulfate) has been used as a mortar for construction
since the dawn of civilization, and is even found in the Egyptian pyramids.
Similar and yet distinct, chalk is a base (an alkali that neutralizes acids) that is
composed of calcium and oxygen combined with carbon, while gypsum is a salt (the product
of a base and acid reacting and both becoming neutralized), made up of calcium and oxygen
combined with sulfur. Both are believed to be formed in similar
fashion. Chalk is a limestone deposit created as plankton (tiny marine organisms) concentrate
calcium in their bodies while living, then leach the calcium out after they die and settle
onto ocean floors; over millennia, large deposits are formed, and as the seas recede, chalks
deposits remain. Gypsum’s origins are similar, but in addition
to being comprised of the calcium produced by the deaths of millions of plankton, gypsum
also contains some of the salt that was left behind as the ocean evaporated.
Traditionally chalk has been used for drawing and writing, and by the end of the 18th century,
with advances in slate quarrying (slate was originally used for writing tablets and blackboards),
writing slates covered with chalk letters, symbols, numbers and figures were commonplace.
Gypsum on the other hand, had been used primarily in construction, such as for the aforementioned
mortar, as well as in the manufacture of windows. Nonetheless, both are susceptible to a process
that produces sticks of themselves that, when pressed against certain services, leave washable
marks. After quarrying, each is crushed, ground,
washed and sifted. With gypsum, it must also be dehydrated in a process that involves high
temperatures to reduce its water content from nearly 21% to about 5-6%; to make classroom
chalk, the material is mixed, again, with water (and colored pigments, if desired),
and to produce more exotic pastels, such as used for art drawings, pigments as well as
clays or oils are also added. For the former, the chalk is baked, while with the latter,
it is air-dried. As to why gypsum has replaced chalk for writing
on blackboards, it is commonly suggested it’s because chalk is much more dusty. However,
modern manufacturing methods, including baking the chalk and coating it with products like
shellac, have reduced the problem for both materials.
The most likely real reason is that gypsum is used for a huge number of applications,
meaning quantity of scale kicks in a bit more, with it being so industrially abundant. The
mineral is mined in more than 90 countries, including Canada, Mexico, Spain and the United
States. In the U.S., 19 states (notably California, Iowa, Nevada, Oklahoma and Texas) have surface-mining
operations, and the U.S. alone produces more than 30 million tons of the stuff each year.
In fact, in 2013, North American gypsum manufacturers reported sales of gypsum board, alone, of
more than $3 billion, annually; together they produced more than 20.5 billion square feet
of drywall, which is found in more than 97% of American buildings.
On that note, sometimes called “the rock nobody knows,” gypsum can easily be turned into a
fine powder (by dehydrating it), while it also has the remarkable quality of being one
of “the only natural substance that can be restored to its original rock-like state by
the addition of water alone.” Since it can be reconstituted, it can be fashioned
into any of a myriad of shapes and modified for various uses. Common applications include
plaster of Paris, creating clay molds from which a variety of plastic products are formed
(such as plastic cups and plates), the manufacture of glass, as an ingredient in cement and in
drywall (this last has been a boon to humanity as gypsum is naturally fire resistant).
Non-toxic, gypsum also pops up in fertilizers and soil conditioners, hair products, to make
plasters of teeth, to grow mushrooms, brew beer and bind tofu (which also has the added
benefit of making bean curd an excellent calcium source).
Bonus Fact: Ever wonder why an elephant’s nose is called
a “trunk”? Well, wonder no more. Naming the elephant nose this first seems to have
happened sometime in the late 16th century. The first documented instance appears in the
1589 work by Richard Hakluyt, Principal Navigations: “The Elephant . . . With water fils his troonke
right hie and blowes it on the rest.” As with most etymologies, the precise reason
trunk is used to denote an elephant’s proboscis is difficult to distinguish with 100% certainty.
However, it’s generally thought it was because a few decades before “trunk” started getting
applied to an elephant’s snout, it was also a word used to describe a pipe or hollow tube,
such as a speaking tube or ear-trumpet. For instance, in the 1546 John Bale work, The
Acts of English Voltaries: “The roode spake these wordes, or else a knaue monke behynde
hym in a truncke through the wall”. Similarly in the 1553 work by Richard Eden,
A Treatyse of the Newe India (which was a translation of part of Cosmographia, by Sebastian
Muenster), where it describes the tubes used for blow-guns “They… blowe them [arrows]
oute of a trunke as we doe pellets of claye.” This “blow gun / hollow tube” usage particularly
fits with the aforementioned first known use of the word to refer to an elephant’s proboscis,
“With water fils his troonke right hie and blowes it on the rest.”
Incidentally, another one-time name for the elephant’s trunk is “boss,” presumed to be
short for “proboscis.” This was first attested in the 1594 Lectures on Jonah, “Curtius writeth
of the elephant that he taketh an armed man with his hand… He meaneth the boss of the
elephant, which he useth as men their hands.” In any event, this might all have you wondering
how the “trunk” of a car got this name. (For the British, we’re referring to the boot of
a car here.) For this, we need to go back to the Latin
truncus, “main stem or stock of a tree or human body.” This, in turn, gave rise to the
Old French “tronc” (“alms box in a church, trunk of a tree, trunk of the human body,
wooden block”) around the 12th century and then the English “trunk” around the 15th century.
It is the “main stem of a tree” definition that is important in this one. By the mid-14th
century, this gave rise to wood chests or cases being referred to as “trunks,” presumed
to be because they were made from wood from tree trunks.
Whatever the case, the first known instance of this definition of the word can be found
in a 1462 receipt (Mann. & Househ): “Item, payd ffor a new tronke ffor my lord whych
was delyvared to Willyam off Wardrope x. s.” Fast-forward a little under a half millennia
later and we find an advertisement in the November of 1929 Hearst International Magazine
where an automobile is listed as coming standard with “Six wire wheels and a trunk rack”. The
rear trunk rack eventually gave way to a built-in storage compartment in the same region of
the car that itself was referred to as a “trunk” in North America.
Another interesting one is the use of “trunks” to refer to an article of clothing, such as
swimming trunks or “shorts.” This general definition for the word seems to have popped
up in the 19th century with the first reference in 1836 in the Pickwick Papers, “The appearance
of Mr. Snodgrass in blue satin trunks and cloak, white silk tights and shoes, and Grecian
helmet.” As for specifically “swimming trunks,” we
have the first instance appearing in a July of 1883 edition of the Pall Mall Gazette where
it states, “Captain Webb attempted his perilous feat of swimming the Niagara Rapids… He
wore a pair of silk trunks…” In this case, it’s generally thought the definition
either stems from the “hollow tube” idea, with the trunks having two hollow tubes to
stick your legs through (hence “trunks” instead of “trunk”), or is referring to the fact that
the shorts contain part of the base of the trunk of the body.