My Science School

Ornaments could be made of pure gold but would get easily pressed out of shape. This is because gold is a soft metal, though it is heavy.

The two terms ‘dense’ and ‘hard’ do not mean the same. Gold has high density, over two times that of iron, because its atoms are heavier. Hardness can be easily demonstrated by ‘scratch’ test.

  A steel knife cannot cut glass, but a diamond tipped steel knife could, because diamond is harder than glass and steel is not. Gold is easily scratched. Haven't we seen goldsmiths assessing the purity of gold by rubbing it against a whetstone and examining the scratch?

 Carat has two meanings: first it is a unit for weighing precious stones. It is almost equal to 200 mg. This is based on the old European practice of weighing precious stones using the seed of a bean pod, somewhat similar ‘Manchadi’ (in Tamil).

Second, carat is a measure of purity of gold. Usually, a bit of copper is added to gold, while making ornaments, to give the hardness and to prevent distortion. 24 carat means 100 per cent gold.

Hence one carat represents 100/24 per cent. Thus 22 carat gold means 9l.67 per cent pure and 18 carat gold 75 per cent; the rest being copper.

Pasteurization is defined as the process of heating milk to a particular temperature and holding it at that temperature for a particular time till the pathogenic (disease causing) micro-organisms are destroyed causing minimum change in composition flavour and nutritive value of milk.

High temperature short time (HTST) pasteurization at 71.7 {+0} C for 15 seconds is the most common method of pasteurization. Pasteurization conditions are not sufficient to destroy thermo-resistant spores (reproductive part of microorganisms). Pasteurized milk has to be refrigerated.

Sterilization is a more severe thermal process where milk is subjected to temperature of about 135 {+0} C for few seconds followed by aseptic (free of micro-organisms) packaging. Milk processed in this manner is termed as ‘commercially sterile’, but it is not necessarily free of micro-organisms.

 These micro-organisms, which survive heat treatment, are unlikely to proliferate during storage and cause spoilage to the product.

 However, spores are destroyed during sterilization. Sterilized milk has longer shelf-life even at room temperature. Nutritional losses in sterilization are more compared to pasteurization. 

 Pasteurization is one of the methods of preservation of products such as milk, alcohol beverages etc. at higher temperatures. The process of heating of the product (milk or beverage) to a controlled temperature (usually below 100 {+0} C) to enhance the keeping quality and to destroy harmful microorganisms is known as pasteurization.

            There are two methods of pasteurization (of milk) in general use. One is low temperature holding (LTH) method in which milk is heated to 62.8 {+0} C (145 F) for 30 minutes in commercial pasteurizers (or) large closed vats which are heated by steam coils, hot water jackets etc.

The other method (i.e.) high temperature short-time (HTST) method in which the milk is heated to 71.7 {+0} C (161 F) for 15 seconds. The heating is accomplished by electricity (or) hot water and requires a heat exchange system, which preheats raw, cold milk and cools the hot pasteurized milk.

Pasteurization does not sterilize the products but kills those organisms that grow most readily at low temperatures. The surviving organisms must be kept from multiplying by constant refrigeration. 

Pasteurization is sterilization interpolated with a subtle nuance in the process conditions and hence in the final result as well.

Pasteurization is named after the great French chemist Louis Pasteur, is the process of partial sterilization, confined only with the killing of pathogens.

The subject is heated to temperature below its boiling point (usually less than 100 {+0} C) and held at that temperature for a particular time period, with the aim of killing only the pathogens.

The time-temperature combination is decided based on the heat resisting capability of the target micro-organism and the nature of the subject. For instance milk is heated to 73 {+0} C & held for 15 seconds, to destroy Coxciella burnetti and Mycobacterium tuberculosis, which are the target micro-organism.

Sterilization is extended pasteurization where the subject is heated above the boiling point and held for a particular time period to destroy all the microorganisms. The temperature is usually above 100 {+0} C.

Plastics are made of polymers which giant molecules are having long chains of repeating units derived from short molecules. These long chains are entangled with are one another and held together by weak inter-atomic forces such as Vander Waals force. These weak bonds can be easily broken up by sunlight and so long exposures to sunlight make them brittle. 

A soap molecule is made up of 2 parts - a long hydrocarbon part and a short ionic part containing - COONa+ group. The soap molecule is said to have a tadpole structure.

 The hydrocarbon part of the soap molecule is insoluble in water but soluble in oil and grease. The ionic portion of the soap molecule in hydrophilic. So the ionic portion of the soap molecule is soluble in water but insoluble in oil and grease. Now the clothes which contain dirt substances are soaked in water.

When soap gets dissolved in water it forms a colloidal suspension in which the soap molecules cluster together to form a micelle. The micelles remain suspended in water because negative charges at the end of each soap molecule repel each other.

In a micelle, the soap molecules are arranged in a radical manner with the hydrocarbon end directed towards the centre and the ionic end directed outwards. When greasy, oily clothes are immersed in soap solution, the soap micelle entraps the dirt particles by attaching the hydrocarbon part of the soap molecules to the greasy or oily particles.

Since the ionic part of the soap molecules remain attached to the water molecules, the dirt particles get dispersed in water and the cloth gets cleaned.

            Soap has been used as a detergent for more than 2000 years. Soap is made from oil or fat which are esters of fatty acids or glycerol. The fatty acids contain chains of 16 to 18 carbon atoms.

            When oil or fats are heated with a solution of sodium hydroxide, they breakdown to form sodium salt of the respective fatty acid and glycerol. The process of splitting the fat is called saponification. It produces soap which is separated from the solution by the addition of salt. A molecule of soap can be considered to be made up of two components. One part is a hydrocarbon and the other belongs to the COONa group.  Hydrocarbons are water repelling - hydrophobic and the other parts are water loving - hydrophilic. When water is dissolved in water it forms micelles. In a micelle, the soap molecules are arranged radically, with the hydrocarbon end towards the centre and the water loving end outwards. Dirt and grease present on a piece of cloth attach themselves to the hydrocarbon component of the soap molecule. The other component which is attached to the water molecules pulls the dirt away from the surface thereby making the cloth clean.

 Washing powder contains about 15-30 per cent detergents by weight. Sodium sulphate and sodium silicate are added to keep the washing powder dry. Sodium tripolyphosphate or sodium carbonate is added to maintain alkalinity which is helpful in removing dirt. Carboxyl methyl cellulose is added to keep the dirt suspended in water. A mild bleaching agent such as sodium per borate is also added to produce whiteness. 

 

Ordinary soap has little value as an antiseptic and it does not kill or inhibit many types of bacteria.

However, the important function of washing one’s hands with soap is the mechanical removal of bacteria through scrubbing.

 The skin normally contains dead cells, dried sweat, bacteria, oily secretions and dust. In addition, having been to the toilet one would probably have contaminated his hands with faecal bacteria.

 Soap emulsifies the mixture of all these and the water washes it away. Because soaps are good for physically removing bacteria from the skin it is important to wash the hands before eating and after going to the toilet.

This prevents the transfer of potentially harmful bacteria by the faecal to oral route.

Cosmetic soaps contain antimicrobial compounds that strongly inhibit gram-positive bacteria and these are used to decrease body odour by preventing microbial growth on body secretions. These are non-household soaps that do contain some type of antibacterial compound.

These compounds act as disinfectants and kill bacteria. Of course, during our everyday activities we do not need or want to completely disinfect or sterilize our skin because the normal population of bacteria on us acts as a barrier against infection by pathogens. Healthy skin is a bacterial battleground populated with friendly bugs. These eat our sweat and, defend our skin from less friendly bugs that would not only eat our sweat but us as well.

Staphylococcus aureus is a typical invader that causes pimples and boils (or worse) when it beats our defenses. When we wash, we not only remove dirt and invasive bacteria, we also release a tide of friendly bugs from pores to recoat our skin for protection. This is fine unless you work in food preparation, you will then be required to use soaps that contain broad spectrum bactericides that kill all types of bacteria indiscriminately. Effective hand washing depends on many factors - the soap or cleaning agent, running water, clean towel or air drier for drying and on good technique.

Normal hand soap can remove germs, if used properly, and left to drain and dry between uses, not left sitting in a puddle of soggy soap and stagnant water. Pump dispensers are generally better than soap bars. Water must be clean and taps must not be contaminated by dirty hands - that is why hospital sink taps have elbow levers or, more rarely, foot pedals.

 Effective rinsing and drying, to remove any contaminated water without adding further contamination from a damp towel, are vital components of proper hand washing technique. This is why disposable paper towels are usually used in hospitals. Studies on hand-washing techniques by nurses have shown that some areas of the hand are less well-cleaned than others - fingers and the web between thumb and first finger are commonly inadequately leaned.a

Zeolite is used in the purification (more correctly softening) of water. Water in some localities contains salts of Calcium, Magnesium and Iron present in the earth. Such water finds it ‘hard’ or difficult to lather with ordinary washing soaps. This is because these salts react with the sodium compounds in soap causing wastage.

Further when such hard water is used in boilers these salts form a coating on the wells. This could be seen even in household vessels in which we use to boil water. Zeolite is the common name for a complex compound Sodium Aluminum Silicate. When hard water is passed through filters containing Zeolite, the salts of Calcium and Magnesium get absorbed and Sodium salts are released in exchange. Special kinds of Zeolite based on Manganese salts could remove salts of iron also if present in water.

 When the softening power of Zeolite gets weakened by constant use, it could be revived by pouring solutions of common salt and Potassium permanganate.

Water contains dissolved salts of calcium, magnesium and often iron in the form of bicarbonates, chlorides and sulphates present in the Earth's crust. When such water is heated, the bicarbonates of calcium and magnesium decompose evolving carbon dioxide and leave behind sparingly soluble carbonates.

Bicarbonate of iron interacts with the carbon dioxide and water forming sparingly soluble ferric hydroxide (brown). These sparingly soluble salts form the layer or ‘scales’ seen in utensils and boilers.

In filters, there is no boiling, still similar chemical changes take place, though to a much less extent, when the remnants of water dry up. Chlorides and sulphates do not undergo these chemical changes, but form residues due to evaporation of the water.

The usual way to avoid this trouble is by using de-mineralized water, that is, ordinary water filtered through permutit (sodium aluminum silicate), manganese salts (to remove iron) and modern ion-exchange resins. The last one frees water from all mineral salts.

All these filters naturally get clogged when in continuous use but can be regenerated in most cases by simple chemical treatment.

Potassium cyanide when consumed causes death by gradually arresting the supply of oxygen to our body cells by forming stable complexes with hemoglobin (present in the blood) and cytochrome (a protein which helps in the respiration of the cells) and depriving them of their capacity to transport or exchange oxygen.

Normally, oxygen is carried to different parts of the body from the lungs by the blood using hemoglobin -the iron-containing, oxygen-carrying molecule of the red blood cells.

Hemoglobin is made up of a globular protein and four heme groups. The iron (in ferrous state) present in these heme complexes can bond to either an oxygen molecule or a water molecule or exchange them one for the other without much difficulty. It is because of this ability to exchange them, hemoglobin is able to pick up oxygen from the lungs, carry it to the body cells and bring back water in return.

The body cells ‘respire’ oxygen with the help of Myoglobin (hemoglobin like proteins present in the cells) and cytochrome (which function as electron carrier). One form of this cytochrome and hemoglobin are responsible for the sudden death due to cyanide poisoning.

When potassium cyanide is consumed, it splits into a potassium ion and a cyanide ion. The cyanide ion has a strong affinity to the ferrous ion than what oxygen has. As a result it occupies the site meant for oxygen in the hemoglobin. This process is irreversible and so it prevents transfer of oxygen.

Also, one form of cytochrome, designated as cytochrome-a, also binds with the cyanide ion and stabilizes the iron to such an extent that it does not take part in the electron transfer to the cell. This prevents oxygen in take by the cell. The symptoms of cyanide poisoning are giddiness, headache and bluish tinge of the skin. All these are indicators of lack of oxygen supply to various parts of the body. If not treated immediately, unconsciousness and death will follow.

Inhalation of amyl nitrate or injection of sodium nitrite to oxidize some of the hemoglobin to methymoglobin provides relief. Methymoglobin binds to cyanide ion more tightly than hemoglobin or cytochrome-a and helps in the removal of cyanide from the system. Carbon monoxide (CO) also has a similar effect when inhaled. It forms a stable compound called carboxy hemoglobin and deprives it of its oxygen carrying capacity. 

Formation of a solution is a physico-chemical process. When two substances mix to form a solution, heat is either absorbed (endothermic process) or released (exothermic process). This depends on various interactions taking place between the solvent and the solute at the molecular level.

 Glucose exists in the crystalline form. When dissolved in water, the crystal structure is broken. To break the bonds in the crystal energy is required. This is obtained from the water itself and so its temperature is reduced. Chemists call this an endothermic process. But considering a similar reaction, the dissolution of salt (sodium chloride) in water.

Though this is also an endothermic process the heat transfer involved is very less. (Moreover there are other interactions of the sodium and chloride ions with water, which are exothermic in nature).

Strong exothermic effects are observed in certain cases where the substances interact strongly with water molecules. For example, dissolution of washing soda (sodium carbonate) or sodium hydroxide. 

Fire involves a chemical reaction between fuel and atmospheric oxygen.  Once initiated it is self-sustaining, generates high temperatures and release a combination of heat, light, noxious gases and particulate matter.

The visible flame is the region in which this chemical process occurs and so flame is essentially a gas phase phenomenon. For flaming combustion to occur, solid and liquid fuels must be converted into gaseous form.

 For liquid fuels this is achieved by evaporative boiling. For solid fuels, the solid is chemically decomposed through the process of paralysis to generate volatile gases.

A flame is a region containing very hot atoms. At high enough temperatures all atoms will emit energy in the form of light as their electrons, which have been prompted to higher energy levels by absorbing heat energy, fall to lower energy states. Because this light is emitted in discrete quanta according to the relationship E= hf (where E=energy, h=Planck’s constant and f= frequency), flame colour is related to the magnitude of the energy quantum which is transformed to light.

This can most easily be seen with a Bunsen burner. A Bunsen burner that has a choked air supply burns cool, the light emissions from carbon atoms are relatively low in energy and appear more red or orange.

However, when the Bunsen is allowed air so that combustion is complete, the flame is hotter and the light emitted is of a higher energy and frequency and appears blue.

The luminescence of a flame is only of the story. The structure of the flame region is important to understand too. The flame area in a normal combustion environment, such as an open-air bonfire, is structured by convention currents which form as hotter, lighter air rises and allows cooler fresh air to replace it.

It is this channeling effect and movement of air that shapes the dancing flames. It is interesting that in space, in zero gravity, the hotter and cooler air cannot move by convection, so flames take on weird shapes and may be stifled by their own combustion products. 

Fingerprint formation is like the growth of capillaries and blood vessels in angiogenesis. The pattern is not strictly determined by the genetic code but by small variables in growth factor concentrations and hormones within the tissue. There are so many variables during fingerprint formation that it would be impossible for two to be alike. However it is not totally random, perhaps having more in common with a chaotic system than a random system.

It is believed that the development of a unique fingerprint ultimately results from a combination of gene-environment interactions. One of the environmental factors is the so-called intrauterine forces such as the flow of amniotic fluid around the fetus. Because identical twins are situated in different parts of the womb during development (although they are not static), each fetus encounters slightly different intrauterine forces from their sibling, and so a unique fingerprint is born.

            Your genes specify only your biochemistry and through it, your general body plan. The pattern of your fingerprints forms rather in the way that wrinkles form over cooling custard. At most you may predict, say, the fineness of the wrinkles and their general pattern. Fingerprints are just one example. Many of your features could mark you out from any clone. Your genome only controls gross characteristics such as the rates at which the skin and its underlying attachments develop and grow. Even if there is no way for genes to specify everything exactly, there is no way the genome could carry enough information for the details. If our genomes had to specify everything, we would not be here. But, while the consequences of imperfect specification are usually trivial, they may have more serious effects. A minor distortion of a blood vessel could give poor blood flow or an aneurysm, and the branching and interconnection of brain cells affect mental aptitudes. That is why, though bright parents tend to have bright children, dimmer ones may have a child genius and vice versa.

Scorpion’s venom acts on the nerve tips and roots whereas snake’s poison acts on dendrites and axons of the nerves. As defence and prey capture are the sole aim of these and other animals and insects, it is the purpose on hand that determines venom’s composition and type.

 Cobra venom consists of 10 different enzymes, several different types of neurotoxins, cardio-toxins, cytotoxins, dendrotoxins and fasciculins (for example, lysocephalins, lysolecithins which are phospholipids). Snakes of the elapidae family (for example cobras, kraits and mambas) have venoms that kill primarily through neuro-muscular paralysis. It contains 60-75 amino acids and target nicotinic cholinoceptors in the muscle cell membranes which are sensitive to a chemical transmitter, acetylcholine. (Acetylcholine is released from nerve endings in response to an electrical impulse in the nerves.) The amino acids in snake’s venom block the junction between the nerves and the muscle. Scorpion’s venom consists of an arsenal of toxic compounds which contain 37 amino acids called charybdotoxin.

            When a scorpion stings these acids incapacitate the nerve cells causing severe pain, by rigidly binding with sulphur bonds unlike the snake’s toxin which binds by a ligand series. Moreover snake’s venom is digestible, but scorpion’s venom is not          

            Plants can prevent pollution of environment in many ways. However, the answer is restricted to prevention of air pollution by trees.

            The major components of atmosphere are nitrogen (78.08 per cent) and oxygen (20.95 per cent) (major) with minor components are argon and carbon dioxide (0.0314 per cent) and many trace elements such as neon, helium, nitrous oxide, methane, carbon monoxide, sulphur dioxide, ozone, ammonia and aerosols (colloidal sized particles) are also present.

            The ratio of these components is changing very fast due to increased human activities like fossil fuel burning, afforestation and changes in land use. They result in the liberation of tones of carbon dioxide, carbon monoxide, methane and aerosols into the atmosphere. The server human interference over the last century is said to have strained the buffering capability of nature.

            Trees help reduce the pollution in more than one way. First, they act as sink for carbon dioxide. Through photosynthesis they synthesize carbohydrates using carbon dioxide, water and sunlight. This way thousands of tonnes of carbon dioxide are trapped by the trees. By the same process, trees release oxygen, which is needed by other living organisms. They also help in cooling of the atmosphere by transpiration, a process in which water is given up by plants as vapour. I addition, aerosols and dust particles (components of atmosphere pollution) settle on the dense foliage of trees. Thus trees, especially the tall ones with dense foliage around houses and industrial establishments, reduce aerosol and dust pollution by acting as barriers or curtains.

   Bitterness is cucumber and other cucurbitaceae vegetable is due to the presence of compounds called cucurbitacins. Chemically these are tetra-cyclic triterpenes having high oxidative levels. They occur in nature as free glucosidesor as complicated mixtures, at high concentrations, in fruits and roots, for example in a wild variety of cucumber called Cucumis hardwikii.

            High temperatures above 92 degrees have been implicated in the increase f bitterness in fruits, although there is no evidence to support this. Conversely more bitter cucumbers are seen growing during the cooler growing season.

         

 

 

 

 

 

  Most of the mushrooms have a cap called pileus and a stem called stipe. The cap on its underside consists of gills which bear the spora producing structures. Important to the identification of a species are the properties of cap, the shape and colour of the gills, the way in which they are joined to the stem, presence or absence of sheath, scales and annulus ring etc. The most poisonous mushrooms are species of Amanita which come under the family Amanitaceae and the most delicious edible mushrooms are species of Agaricus (Button mushroom) which come under the family Agaricaceae. In general the fruit bodies of Amanita species can be distinguished from the Agaricus species by the following characters.

In Amanita species the pileus on its upper surface bears the scales and the stipe bears at its base a sheath called Volva. These scales and sheaths are absent in the fruit bodies of Agaricus species.

Volvariella (Paddy straw mushroom) is also having Volva at the base of the stipe as in Amanita. But it is an edible mushroom and also commonly cultivated. The Oyster mushroom namely Pleurotus is another edible one. This can be identified by its stem at the side of the cap and gills on the under surface of the cap. Boletus (Penny bun mushroom) and Lactarius (milk cap) are also edible members which grow in wild condition but not cultivable. Among these Boletus can be identified by its dense layer of tubes instead of gills on the underside of the cap.

The familiarity in distinguishing the poisonous and nonpoisonous mushrooms is needed only when we collect the wild fungi from the field for our diet table. But this problem will not arise in the case of edible fungi which are cultivated for this purpose.