Abrasives, Fertilizer Chemistry, Pesticides | Science & Technology for UPSC CSE PDF Download

Abrasives/ Natural Abrasives

Abrasives are substances or objects that are employed to wear off or rub down other objects, in order to give them the desired size, shape or finish.

Examples of natural abrasives are: 

(i) Diamond  (ii) Corundum  (iii) Energy  (iv) Garnet  (v) Pumice  (vi) Quartz  (vii) Flint  (viii) Sand stone and sand.

Examples of Synethic Abrasives are: 

(i) Silicon carbide (ii) Fused alumina (iii) Boron carbide (iv) Metallic abrasives.

Uses of Abrasives 

(i) Coated abrasive (ii) Polishing, buffing and lapping (iii) Sharpening sticks (iv) Grind stones and Mill stone.

Fertilizer Chemistry

So far 16 elements are known to be essential for plant growth and reproduction. 7 elements needed in quantity (macro-nutrients) are: hydrogen, oxygen, nitrogen and carbon from air and water and phosphorus, potassium and calcium from minerals in the soil. 9 elements needed only in small amount (micronutrients) are: magnesium, sulphur, boron, copper, iron, manganese, zinc, molybdenum and chlorine. The effect of manure in the soil persists for long period but their action is slow.

The effect of fertilizer remains only for a short period but their action is very swift. Nitrogen (N), phosphorus (P) and potassium (K), the primary plant nutrients are commonly applied to soils in the form of commercial fertilizers and hence they are known as fertilizer elements.

Nitrogenous Fertilizers

These are ammonium sulphate or nitrate, calcium ammonium sulphate, urea, calcium cynamide, etc. These provide ammonia which is converted to nitrates by soil bacteria and stored as plant food. Nitrogen growth increases, yield, increases protein content, imparts dark greencolour to leaves and improves quality of plants.

Phosphorus fertilisers

The nickname of phosphorus fertiliser is the “masterkey to agriculture”. Common phosphorus fertilizers are: super phosphate, diammonium phosphate, Basic slag, Bone meal, and rock phosphate — Fluor - and Chlorapatite. Its use in alkaline soil is not suitable.

Potash Fertilizers

Potash fertilisers show good results on sandy gravelly or chalky coils. These are specially sued for meadow grass, tobacco, cotton, coffee, corn and potatoes. Chief potash fertilisers are: Potassium chloride (Muriate of potash), potassium sulphate, Kainite and wood ashes. The sugar content or beets is lowered as in the quality of potatoes and the burning quality of cigar leaf tobacco when potassium chloride is used as fertiliser.

Pesticides

Pesticides are of 3 kinds.

1. Fungicides,
2. Herbicides, and
3. Insecticides.

Fungicides

They destroy or prevent the growth of Fungi. The most important Fungi cides are the compounds of sulphur and copper. Some fungicides are: Bordeaux mixture, copper sulphate, mercuric chloride, formaldehyde, chloranil, carboxylic acids, alcohols and phenols. Mercuric chloride is extensively used as a means for the control of scab in seed potatoes.

Herbicides

A pesticides either organic or inorganic used to destroy unwanted vegetation, especially various types of weeds, grasses and woody plants. Herbicides may be of two major types:
Selective such as 2-4 D, 2-4 5-T Phenol S, carbonates and urea derivatives permitting elimination of weeds without injury to the crop. 
Non-selective comprising soil sterilants (sodium compounds) and siluicides (ammonium sulphate). The latter kills wood plants and trees. Some types act as overstimulating growth hormones. 
Many herbicides are toxic, and should be handled and applied with care, use of chlorinated type may be restricted.

Insecticides : A type of particle designed to control insect life that is harmful to man, either directly as disease vectors, or indirectly as the destroyer of crops, food products, or textile fabrics. General types are as follows:

(i) Inorganic: Arsenic, lead, and copper, the use of these have diminished sharply in recent years because of the development of more effective types that are less toxic to man.

(ii) Natural Organic Compounds. Such as rotenone and pyrethrins (relatively harmless to man, since they quickly decompose to non-toxic compounds), nicotine, copper-naphthenate and petroleum derivatives.

(iii) Synthetic Organic Compounds: (a) Chlorianted hydrocarbons, such as DDT, dieldrin, chlordane, indane, p-dichlorobenzene. (b) The organic esters of phosphorous (the parathious and related substances).

Another group of organic compounds, of which imidazole is typical, act on the principle of metabolic inhibition. Besides direct application these can be fed to growing plants, with the result that plants can no longer seve as nutrients of the specific insect. 

BHC (Benzene hexachloride) is another compound that has been recognized as an excellent organic insecticide. The chemicla name for BHC is 1, 2, 3, 4, 5, 6 hexachloro-cyclohexane, BHC may exist in sixteen possible isomeric forms and is more volatile than DDT and has been proved to be highly effective insecticide. 

Chlordane is another organic compound that has been used quite successfully as an insecticide. It has been found to possess many of the properties exhibited by DDT. It is toxic to animals. 

Petroleum oils have been used as an insecticide for many years.