Category Technology

The bristles of a shaving brush are bunched together to ensure that there are a large number of thin columns of air in-between them. When the brush is moved to and fro, the soap solution seeps into the brush, due to surface tension, partially filling the air columns.

 While shaving, the soap solution stuck to the skin is dragged to form thin films. But when stretched beyond a certain length, limited by surface tension, the films break and in that process trap a little bit of air to form small bubbles. As there are hundreds of bristles involved in the bubble making process, we get lather within a short time.

 The same principle applies to tooth brush and the brushes used for washing.

 

Honey is a very dry product, mostly sugar. Any water that comes into contact with it will be drawn in by osmosis. As a result, most bacteria are dehydrated, killing them or rendering them weak and fragile.

 Bees also treat the honey with an enzyme that generates free radicals, in effect sterilizing the honey with hydrogen peroxide.

In ancient times, honey was sometimes used as a wound dressing, and some modern doctors still use sugar. Experts say the treatment probably works because sugar dries the bed of the wound to promote new tissue growth and dehydrates the bacteria that cause infection.

There are commercial wound pastes made of synthetic microscopic water-absorbing, bends that do the something. 

Honey is adulterated by way of adding jiggery syrup. To verify whether honey is pure, take a glass of water and pour one tablespoon of honey in it. Gently shake the glass (note not to stir). If the honey completely dissolves in water it is adulterated, On the other hand if it stays as a mass, it is pure honey. 

Generally a substance dissolved in a liquid lowers the freezing point or melting point of that liquid. When salt is added to ice at room temperature, some of the ice melts and cools the salt to zero degrees Celsius. The salt solution produced cannot remain in equilibrium with ice at zero degrees. It is possible only when the ice is at the freezing point of the solution (less than 0 degrees Celsius). So more ice in contact with the salt solutions melts taking the necessary latent heat of fusion from the salt solution, whose temperature is consequently lowered.

More salt thus dissolves, keeping the solution saturated and the process continues till the temperature of the solution reduced to -21 degrees Centigrade. Only at this point (eutectic point) ice is in equilibrium with saturated salt solution. When 23 per cent of salt is added to ice, the freezing point is lowered to -21 degrees.      

         

Solid ice exists at zero degrees Celsius and salt at room temperature which is bound to be higher. So, when the two mix, ice begins to melt. But the temperature still remains at zero. A little of the salt dissolves in the water thus formed. In this process, the fine, solid particles of salt breaks down to positive sodium ions and negative chloride ions (dissociation). This change requires energy which is absorbed from the solution which is cooled below zero degrees Celsius. As more and more salt dissolves, temperature goes down further till -21 degrees Celsius is reached. At this stage, the solution is saturated, that is, the maximum solubility of salt at that temperature has been attained. Ice, solution and salt co-exist at this point called eutectic point.

This principle is used in making freezing mixtures which provide sub-zero temperatures. If calcium chloride is employed instead of sodium chloride, temperatures as low as -55 degrees Celsius could be obtained.

 Another application of salt and ice is in de-icing of roads during winter. The smooth, slippery surface of ice is dangerous to fast moving vehicles. When salt is thrown on the ice, it dissolves and the solution though at a low temperature flows away leaving the roads free. Because of the presence of about 3 percent of salts (chiefly common salt) sea water freezes at -2 degrees Celsius instead of at zero.

   

Salt is used to melt ice on roads and sidewalks. On contact with ice, some of the salt dissolves.

The salt solution has a lower freezing point than pure ice and exists as a liquid at zero degrees Celsius. So even on a cold day, the ice can be melted drained using salt.

One can use sodium chloride (common salt) and calcium chloride for the above purpose. The depression of the freezing point depends on the number of particles in a given amount of solvent.

Electrolytes are compounds which produce ions in solution. NaCI exists as a sodium ion and a chloride ion in solution and calcium chloride as a calcium ion and two chloride ions. Among these the calcium salt is better clearing ice from sidewalks as it produces more particles (three ions – one calcium ion and two chloride ions) in the solution. But we cannot use them for cleaning ice in automobile radiators because of their corrosive nature. For that ethylene glycol is used as antifreeze even though it is not as efficient as the calcium salt. 

Obviously because of the string and the tail. How the string is tied to the sheet of paper (at certain angles) plays an important role in the successful flight of the kite. First, the sheet of paper is made stiff using thin sticks so that it does not bend due to the forces of the wind. Next, 3-4 small strings of equal length are attached. All this is to make the kite fly at an angle with the direction of the wind.

According to the laws of physics, any force acting on can be separated into two components – one horizontal and the other vertical. Generally the vertical component lifts the object (against gravity) and the horizontal component pushes the object (along the direction of the force). Here the force acting on the kite is due to the wind.

 In the case of pieces of paper, the wind force blows them away as they are not secured anywhere. But in the case of the kite, it is held by the string in on e direction (a restoring force) and the wind is exerting its force in the opposite direction.

 The net force on the kite is resolved into the horizontal and vertical components mentioned above. These force components depend on the angle of the kite’s axis to the wind direction. When the lifting force is sufficient enough, the kite begins to fly. 

 At times we pull the string or run into the wind. These are tricks to increase the lifting force and make the kite fly higher. Some kites tend to rotate along the axis of the string. To prevent this rotation, a long tail is attached.

 The flight of the kite may look simple going by the above explanation. But there is a lot more to it: For example, if we closely watch the flying kite we can see that it is very dynamic. It adjusts its position continuously depending on the movement of the air surrounding it. All this it does, may be because it wants to fly! 

            In most cases dirt adheres to the fibres of textile fabrics by 2 kinds of forces – first by sticking to a coating of grease or a dried coating of substances which swell up in water or other solvents (starch, Proteins and other glue like substances); second by direct adhesion because of the physico – chemical character of the fibres and the dirt. Dirt consists of fatty substances, proteins, and dust and soot particles. Such dirt is largely insoluble in water or is water repellent. Used shirt is soiled with greasy substances constituting about 0.25 percent of its weight; collar may contain as much as 1.2 percent of its weight of greasy dirt.

The dirt may be held by the fibres in various ways; mechanically (pigments are jammed between fibres), chemically (fruit oil or ink strains) by absorption (feebler chemical band, dissoluble by detergents) and by electric forces. As most of the dirt is firmly held by the fibres, pure water is not very effective. Chemical cleaning or dry cleaning uses liquids other than water for cleaning of fabrics. In this treatment adhering dirt of the first kind is removed by dissolving the grease or their sticky matter to which the dirt particles are clinging.

A wide range of solvents are employed: carbon tetrachloride, trichloroethylene, tetrachloro ethylene, naphtha (petroleum ether) and benzene. A modern dry cleaning plant comprises a number of specialized machines and appliances. The soiled garments are treated with the solvents in rotating drums.

Contaminated solvent is drained off and purified for re-use. Cleaned garments are dried, impregnated and reshaped. In some cases, however, it is necessary to use water as an additional solvent or swelling agent.

The second type of dirt is dislodged from the fabric by means of detergents added to water. After this wet treatment the fabric is usually treated in weak acid solutions (to revive colours). Rinsed, centrifuged and dried.

Impregnation treatment may be applied at an intermediate stage to stiffen the fabric and make it water- and dirt-repellent. Garments are finally pressed on special machines operated with steam and air. 

      Fabrics such as cotton and linen are treated with thermosetting resins such as urea formaldehyde and melamine formaldehyde to get a durable finish, writes Mr. Surya Kumar of Tuticorin.

A thermosetting resin is a plastic that Solidifies when heated under pressure. They improve the capacity of the fabrics to resist and recover from creases formed during wear. According to him, only when clothes are pressed by a heated iron, under slight pressure, the resins develop cross linked chains between them which give stiffness to the clothes. A cold iron will not be able to do that.

Dr. J. Venkat Rao, Head of the Department of Textile Technology, Anna University, Madras, says  that  this explanation holds good only for certain fabrics. There are a few other factors which are to be considered for ironing clothes, he says.

The first is moistening the cloth. The water makes fabrics such as wool or silk to swell whereas it imparts plasticity to polyester. This allows the fabric to set in any predetermined pattern when pressed with a hot iron box. Because of the heat the moisture evaporates and the cloth sets neatly (as it is made mouldable) as the creases are removed.

According to Dr. Rao, different kinds of clothes are capable of withstanding varying quantities of heat. Natural fabrics such as cotton and linen are not thermoplastic by nature and hence are capable of withstanding high temperature. Synthetic fabrics such as nylon and polyester are thermoplastic. They melt at even slightly high temperatures and hence too much heat should not be applied to these fabrics. Another factor that controls ironing is the pressure applied – heavier iron boxes can exe greater pressure. This explains why dhobi’s ironing is far better than the housewife’s.

A soft bed above a hard surface perhaps helps in distributing the pressure evenly on the cloth.