A closer look
Deliquescence: at a glance
The Deliciousness (from the Latin verb Let's go. = to dissolve, liquefy, composed of the strengthening prefix de- and from the verb I'm gonna be here = to become liquid) is a specific chemical-physical property of some solid substances (mainly Sale or strong bases) to absorb atmospheric moisture until completely dissolved in it, forming an aqueous solution. The phenomenon occurs when the steam pressure of the saturated solution of the substance is lower than the partial pressure of the water vapour present in the surrounding air.[1] It is also a peculiar characteristic of meat of some species of basidiomycete mushrooms, in particular the order Agaricales.
Chemistry and physics
Thermodynamic mechanism · Examples of deliquescent substances · Differences with efflorescenceExplore this chapter
Deliciousness is an extreme form of igroscopy. While a hygroscopic substance simply absorbs water (becoming moist or hydrating without changing its physical state), a deliquescent substance absorbs such a quantity as to exceed its solubility limit, passing from the solid to the liquid state.
Thermodynamic mechanism
The process is governed by the balance of steam pressures. A solid substance begins to manifest disappointment when relative humidity (UR) of the environment exceeds a critical value, specific for each substance and dependent on temperature, called point of deliquescence or relative humidity of deliquescence (DHR, from English Deliquescence Relative Humidity).[1] From a thermodynamic point of view, dissolution is often an exothermal process (leave heat). The temporal phases of the phenomenon are four:
- absorption: water molecules accumulate on the crystal surface by adsorption;
- dissolution: a thin layer of saturated solution is formed on the surface;
- progression: since the steam pressure of this saturated solution is lower than the pressure of atmospheric water vapor, water continues to condense in the solution;
- balance: the process continues until the salt is completely dissolved and the solution diluted to the point that its steam pressure equals the partial pressure of water in the air.
Examples of deliquescent substances
Many chemical compounds present this property, making it complex to store in uncontrolled environments. Some examples include:
- Calcium Chloride (CaCl2): widely used in domestic crystal dehumidifiers due to its high affinity for water.
- Magnesium Chloride (MgCl2): responsible, together with calcium chloride, for the packing of whole sea salt and its tendency to become moist.
- Zinc chloride (ZnCl2): one of the most important commercial zinc compounds, extremely soluble.
- Sodium hydroxide (NaOH) and potassium hydroxide (KOH): strong bases which, if exposed to air, quickly translate and form extremely corrosive caustic solutions.
- Potassium Carbonate (K2CO3): the main component of potash and pearl ash.
- Sodium Carbonate (Na2CO3): a moderate alkalizing reagent, also called Soda.
- Ammonia Nitrate (NH)4No.3): a chemical compound that is used as a fertilizer, but also to produce ammonal and ANFO mixtures, two explosives; its deliquescence can compromise the stability of detonating mixtures.
Differences with efflorescence
Deliciousness is the opposite phenomenon toefflorescence. The latter occurs when a hydrated salt loses crystallization water molecules to the atmosphere (because its vapor pressure is higher than the ambient one), transforming into a dry, opaque powder. While deliquescence requires high humidity, efflorescence typically occurs in dry air conditions.
Mycology
Relevant speciesExplore this chapter
In mycology, deliquescence describes a biological process of self-management (autolysis) of the tissues of the sporophurus (the fruit body), typical of some families of mushrooms, in particular the Psathyrellaceae (once grouped in the genus Coprinus). Although many fungi, including AScomycota, may appear "liquefied" during the decomposition process at the end of their life cycle, deliquescence proper is a functional distinctive trait of only some Basidiomycota.
In the "coprinoid" basidiomycetes, spores are produced on the bases located on the faces of extremely thin and parallel lamella. In these mushrooms, the distance between the lamella is so reduced that the spores, once expelled violently (through the mechanism of Drop of Buller), would remain stuck in the interlamellar space.
- in the other basidiomycetes the hat opens to umbrella or the slats are spaced, allowing gravity to drop the spores.
- in the delicious basidiomycetes the hat remains often bell-shaped and the lamella remain thick; the enzymatic dissolution of the fabric (starting from the margin to the center) frees the spores, allowing them to reach the air.
Unlike the chemical phenomenon, fungi deliquescence is an active enzymatic process. When the spores reach maturity, the secerne mushroom ferments (mainly chitinase and glucanase) that degrade the cell walls of the lamelle and hat. This process transforms the mushroom meat into a viscous liquid, similar to black ink.
This mechanism of tissue liquefaction is an evolutionary strategy for spore dispersion. In "coprinoid" mushrooms, the lamella are extremely thick to maximise the production surface; however, this conformation would prevent spores from falling freely by gravity. Deliciousness solves this physical bond through a coordinated dissolution, so that:
- the maturation of the spores occurs sequentially (centripe) from the bottom up along the lamella;
- while the spores are released, the underlying fabric "dissolves", drips and curls, leaving free space to the spores of the upper layers to be transported by the air currents (anemocorous disperse);
- the resulting black liquid, rich in residual spores, can also adhere to the legs of any insects, favoring a zoocorous dispersion (specifically, entomocora).
Relevant species
The deliquescenti mushrooms are not common and are represented by some main genera and species:
- Coprinus comatus (crown mushroom or ink mushroom): edible when young, but deliquescent within a few hours after harvesting. The decay is visible macroscopically and follows precise chromatic stages:
- immature phase: the hat is white, firm, with white or pinkish stripes;
- start maturation: the edge of the hat begins to darken becoming pink-blackish and to curve outwards;
- liquid phase: the hat gradually dissolves in a viscose black cuff. At this stage, the fungus is no longer edible, as protein degradation processes alter organoleptic and biochemical properties.
- Coprinopsis picaceus: the larger species of the genus Coprinus, with a blackish cap dotted with showy white plaques which represent the residue of the original veil. It melts into a thick dark latex.
- Coprinopsis atramentaria: toxic species when consumed with alcohol (covery syndrome), known for the rapidity with which the hat turns into "ink".
- Genre Parasol: small mushrooms that present such a fast deliquescence to disappear a few hours after birth (mushrooms ephemeral).
In addition to the above mentioned Psathyrellaceae, the phenomenon is observed in different intensities in:
- Family Bolbitiaceae: some species of the genus Conocy show signs of early deliquescence.
- Genre Lacrymaria: the name itself (from Latin lacry = tear) comes from the tendency of strips to secrete droplets of black liquid loaded with spores when moisture is elevated.
The liquid derived from the deliquescence of Coprinopsis atramentaria and of Coprinus comatus was historically used as ink to write. This natural ink was particularly appreciated because the presence of microscopic spores inside it made autograph documents difficult to falsify (a sort of "organic signature"before its time).
Industrial and laboratory applications
The ability of certain substances to seize water from the surrounding environment is exploited in different areas:Explore this chapter
The ability of certain substances to seize water from the surrounding environment is exploited in different areas:
- Dryers: in the laboratory, substances such as calcium chloride or phosphorus pentoxide are placed inside dryers (often vacuum) to maintain a moisture-free atmosphere for other samples.
- Dust control: in dirt roads or equestrian arenas, calcium chloride is sometimes scattered to maintain wet soil and reduce dust lifting, exploiting its ability to capture night humidity and retain water for a long time.
- dehumidification: the common salts hygroscopic for domestic use use use the principle of deliquescence to collect excess water vapour in special collection tanks in the form of brine.
Notes
Explore this chapter
- ^ to b (EN) deliquescence, in IUPAC Gold Book. Retrieved 10 March 2013.
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