The terms hygroscopic and hydroscopic may sound similar but their meanings completely differ from one another.
Hygroscopic substance refers to the substance that can take and hold moisture from the surroundings. Hydroscope is an instrument used to see objects deep underwater. This article discusses about hygroscopic vs hydroscopic substances in detail.
Hygroscopic vs Hydroscopic:
| Aspect | Hygroscopy | Hydroscopy |
|---|---|---|
| Definition | The ability of a substance to absorb moisture from the surrounding environment. | The practice of observing objects underwater. |
| Scientific Relevance | Significant in chemistry, physics, material science, meteorology, and various industries. | Relevant in marine biology, underwater archaeology, and maritime activities. |
| Key Examples | Substances like salt, sugar, honey, and certain chemicals. | Instruments like traditional and modern hydroscopes. |
| Applications | Used to control moisture in food and pharmaceuticals, in humidity sensors, and in maritime cargo management. | Used for studying marine life, archaeological underwater exploration, and inspecting underwater structures. |
| Instruments/Tools | Hygrometers and other moisture measuring devices. | Hydroscope and various underwater viewing devices. |
| Historical Background | Long-standing concept in the scientific study of moisture absorption. | Originates from the invention attributed to Hypatia of Alexandria for underwater observation. |
| Physical Process Involved | Involves absorption or adsorption of water molecules. | Involves visual observation through a medium (like water) using specialized equipment. |
| Industries Impacted | Food processing, pharmaceuticals, construction, and maritime industries. | Marine biology, maritime exploration, and underwater archaeology. |
Hygroscopic substances
Hygroscope refers to the phenomenon of attracting water molecules via absorption or adsorption. Hygroscopic substances are capable of taking away moisture from the surroundings and holding it. This decreases the relative humidity of the surrounding. The relative humidity of substance is directly proportional to the amount of moisture the substance can hold.
Engineering materials like ABS, Cellulose , Nylon etc are hygroscopic in nature.In some composites, due to difference in hygroscopic properties of two materials, there can be detrimental effects such as stress concentration. The amount of moisture taken by a substance is a function of temperature and humidity of the surrounding.
The rate of transfer of moisture decreases as it approaches equilibrium. This happens because of two reasons- the driving force behind moisture transfer decreases and the diffusional resistance to mass transfer increases as the surface taking up moisture nears to equilibrium.
Image credits: Wikipedia
Storage of hygroscopic materials
Hygroscopic materials are usually stored in sealed bags. These bags are simply kept in those places where the moisture content has to be regulated. A common example is silica gel which is used to take away moisture content from the products such as water bottles, lunchboxes, water filters etc.
If these materials are not properly stored, the desired moisture content will not be achieved. Moisture content is an essential factor for determining a machine’s life. If it is not regulated properly then simply because of improper moisture content, life of machines will be altered.
Hygroscopic materials in different pressure conditions
The partial pressure of hygroscopic materials and the ambient pressure can affect the moisture of the system directly.
When the material is subjected to high pressure (isothermally beyond saturation point), then the specific humidity will decrease and relative humidity will keep on increasing. The added moisture will affect material’s quality. An example of such pressure fed system is pneumatic system wherein the hygroscopic material is conveyed through air.
When the material is subjected to negative pressure, the specific humidity remains constant and relative humidity decreases as pressure of the air in conveyer decreases.
Applications of deliquescent materials
The phenomenon of absorbing moisture up to such an extent that the substance dissolves completely in the water to make a solution. Liquids like Sulfuric acid and and salts like Sodium Chloride are examples of deliquescent substances.
In chemical industries, deliquescent materials are used for absorbing water content from chemical reactions. These materials are also known as desiccants. Desiccants like silica gel are used for absorbing moisture from the surrounding environment.
Hydroscopy
Hydroscopy is completely different from hygroscopy. Hydroscopy is the practice of looking and observing things underwater. This can be done by using the instrument called hydroscope. The original hydroscope was invented by Greek scholar and scientist philosopher, Hypatia of Alexandria.
Hydroscope itself is not any instrument. Hydroscope refers to the type of any instrument that is used to measure properties related to water. The hydroscope is generally made out of tubes and a transparent cap at the end made of plastic or glass for viewing.
It is difficult for humans to see underwater without using hydroscope. When we try looking underwater with naked eye, water rushes on the surface of eyeball and distorts the light coming to the pupil. Hydroscope prevents this distortion by providing a transparent material which allows light to enter the eye and avoiding contact with water. If required, we can also achieve magnification underwater.
Examples of hydroscopy
Complexity of hydroscope varies from application to application. It can be as simple as a tube with two lens and as complex as a computer controlled lens with variable magnification.
Some examples of hydroscopy are as follows-
- For viewing objects near the surface of oceans, a long tube is fitted with lenses so as to see the objects that can’t be seen otherwise.
- In defence practices, subsurface water is detected by the use of surface nuclear magnetic resonance technique.
Applications of hydroscope
Hydroscopy is an important technique that allows us to study aquatic life and perform underwater tasks. Everything that requires deep water excursions is achieved by using hydroscope.
Following are the applications of hydroscope-
- Scientists use hydroscopes for looking at marine life which dwells deep inside the ocean. Many marine animals and plants have been discovered with the use of hydroscopes.
- Archaeologists use hydroscopes to search for ancient remains which might have submerged deep underwater.
- Hydroscopy is used for inspection of ship hulls and underwater pipelines to check for corrosion.
- Rescue missions in caves which are flooded by seawater.
Hi ….I am Abhishek Khambhata, have pursued B. Tech in Mechanical Engineering. Throughout four years of my engineering, I have designed and flown unmanned aerial vehicles. My forte is fluid mechanics and thermal engineering. My fourth-year project was based on the performance enhancement of unmanned aerial vehicles using solar technology. I would like to connect with like-minded people.