When we talk about "solvents" we denote liquid organic chemicals which dissolve solid substances in them. Solvents can be prepared from organic sources like citrus solvents and turpentine. However, majority of them are drawn from petroleum or other artificial substances. They are extensively used, as they are effective in dissolving materials such as plastics and resins. In addition, they also disperse cleanly as well as quickly.
Solvents can be categorized into two major types - polar and non-polar solvents. On one end, the molecules of polar solvents have a positive charge, while the other end has a negative charge. This is primarily owing to the fact that one atom of this type of solvent has a tendency to draw negatively charged electrons, while allowing the remaining electrons of the molecule to move to the positively charged atom. This is caused by oxygen, particularly when it binds with hydrogen. As a result several liquids having oxygen-hydrogen bonds, like water, are categorized as polar solvents. In addition to water, other liquids like acetone, ethanol and methanol are also polar solvents.
On the other hand, the molecules of non-polar solvents have very little electrical polarity. Some examples on the second type of solvents include various hydrocarbons like benzene, hexane, pentane and toluene. Since these liquids only have carbon-hydrogen bonds, they do not have atoms that tend to draw the electrons away from one another. Chloroform is also a common non-polar solvent. Generally, the polar solvents are very effective in liquefying polar as well as ionic compounds. However, they do not dissolve non-polar substances. The opposite happens in the case of non-polar solvents. Nevertheless, there are several differences even within both these types of solvents. In fact, a number of solvents are extra polar in nature compared to others.
Aside from polar and non-polar variants of solvents, there is a third type too called oil solvent. Precisely speaking, oil solvent is a chemical that dissolves petroleum products like oil. After breaking down the petroleum products, oil solvents leave behind an oil-free, clean finish on machinery, metal parts and even on the floor. Oil solvents are often used for cleaning various metal parts once they are machined. They are used for getting rid of all remains of oil-based coolants employed in the machining processes.
Several popular laundry detergents available in the market for domestic washing machines have any of the above solvents. Some may even contain a number of different solvents for more effective cleaning. Generally, cleaners meant for grease-cutting floors are employed for removing oil spots from a concrete shop floor or garage effectively. Specific types of oil and grease solvents are employed for making paints for metal surfaces. This is done to make sure that paint applied on the metal surfaces does not form blisters or bubbles.
Several solvents that are made for removing oil and grease are basically derived from petroleum products and categorized as oil solvents. In fact, one good solvent available in the market for doing away with oil traces from metallic surfaces is usually not sold in the form of a solvent. This solvent is dubbed as diesel engine starting fluid, often referred to as ether. This solvent is known to be highly successful oil solvent. Usually a very small amount of this oil solvent is misted over any oily surface and subsequently mopped using a clean and soft cloth, thereby making the surface oil-free. There are a number of other cleaners that are employed for removing oil and grease stains from concrete surfaces. These cleaners are, however, not based on petroleum products.
Aside from the solvents discussed above, usually a number of mild acids are also used for cleaning concrete surfaces. Such acids are said to be excellent for substituting for oil solvents. Petroleum-based products such as turpentine and mineral spirits are also very effective solvents, provided they are used in the proper way. However, one should be careful while using most solvents because our skin may easily absorb these chemicals. When this happens, it often results in itchy rashes, as the chemical composition of these solvents is smaller compared to the oil's chemical makeup. As a result, the solvent is able to break into the oil and eliminate the oil from the bottom up. This enables the solvent to get into the skin easily, thereby resulting in irritation. Therefore, it is important to wear protective gloves while handling such solvents.
It is worth mentioning here that there are no solvents that can be described as "safe". The fact is that all solvents, irrespective of whether they are derived from natural products or synthetic, are noxious. Inhaling or coming in contact with the vapour emitted by any solvent is dangerous.
Generally speaking, all solvents can cause irritation as well as damages to the skin, respiratory tract and eyes. Moreover, they may also be responsible for narcotic consequences on our nervous system and, at the same time, harm the internal organs like the kidneys and liver. Aside from these, a few solvents are mainly dangerous for particular organs or may even be responsible for the development of specific diseases, including cancer.
The bad news is that each and every variety of solvents is capable of dissolving the oils that form the protective barrier of our skin. This may result in the skin becoming dehydrated and chapping of the skin, thereby causing dermatitis. Moreover, a number of solvents even cause irritation of the skin when they burn the epidermis. Limonene and turpentine, which are both natural solvents, are known to be responsible of skin allergies. There are many solvents that may not cause any symptom, but still penetrate the skin, go into the blood stream, move all over the body causing various damages to our internal organs.
Vapours emitted by all solvents may cause irritation and harm the sensitive membranes present in our eyes, throat and nose. When one deeply inhales the vapours emitted from the solvents, it may even harm the lungs. Since the solvents emit the vapours into the atmosphere, the irritation caused by coming in contact with them differs depending on the concentration of the vapour of each solvent in the air. It has been found that usually workers using these solvents are not aware of the effects of their vapours when they are present in low concentrations. The only symptoms experienced by people are frequent incidents of colds and infections of the respiratory tract. When one is exposed to such low concentration vapours continuously for many years, he/ she may develop chronic lung ailments like chronic bronchitis.
You should be aware that all varieties of solvents are capable of affecting the brain or our central nervous system (CNS) negatively, thereby leading to "narcosis". The instantaneous symptoms related to the negative effects on the CNS may comprise headaches, irritability, dizziness, nausea and fatigue. As the concentration of the vapours increases, the symptoms too become more serious and may range from experiencing drunkenness to falling unconscious. In some cases, it may even cause death. People who are continuously exposed to solvents for several years may experience irreversible damage to the central nervous system, giving rise to depression, apathy, insomnia, memory loss and various other psychological disorders, which cannot be easily distinguished from the difficulties faced by people in their daily lives.
In addition to damaging the CNS, solvents and the vapours released by them into the atmosphere may also harm our peripheral nervous system (PNS) - the nervous system formed by nerves originating from the spinal cord and leading to the arms and legs. The symptoms related to damage to the PNS include weakness, lack of sensation and irritation in the extremities and even paralysis. A number of solvents like n-hexane, which is present in several spray products and some rubber cements, may cause damages to both the CNS and PNS. When this occurs, the symptoms are akin to that of multiple sclerosis.