3.7. Answer the questions to the text.

1. What did men do at a time when the use of explosives for blasting was unknown?

2. How many people were needed to secure 3 tons of silver per year from the Rio Tinto mine?

3. How many years did the work of 30,000 labourers require to drive a 3,5 miles long tunnel?

4. How many men and years would it take to drive such a tunnel using modern methods and explosives?

5. What was the rate of driving the Cascade tunnel?

3.8. Read and memorize the words.

acid	n	кислота
charcoal	n	древесный уголь
combustion	n	горение, воспламенение
convert	v	превращать
grain	n	зерно; fine grain – мелкое зерно, coarse grain – крупное зерно
gun-cotton	n	пироксилин
gunpowder	n	порох
cap	n	капсюль-детонатор, воспламенитель
exert	v	оказывать влияние
oxygen	n	кислород
potassium	n	калий
powder	n	порох, пыль
substance	n	вещество
sodium	n	натрий
sulfur	n	сера
volume	n	объем

3.9. Read the text “Commercial Explosives” and answer the following questions.

1. What materials supply oxygen for combustion and explosion? (1)

2. What mixture makes dynamite? (2)

3. What classes are explosives separated into? (4)

4. Is the black powder used in blasting at present? (5)

5. What explosive was named after its inventor? (7)

6. When was nitroglycerine discovered? (9)

7. Is nitroglycerine used in mining operations? (10)

8. Where is it used? (10)

Commercial Explosives

1. Oxygen for combustion or explosion can be supplied by substances other than air. Materials widely used for this purpose are sodium nitrate and ammonium nitrate. If sodium nitrate, charcoal and sulfur are mixed in the proper proportions, a mechanical mixture called black power is formed. When confined and ignited, the power explodes and produces hot gases of sufficient volume to exert a strong pressure against the surrounding material.

2. If substances like cotton, starch or glycerin are treated with nitric acid, the resulting products are called nitrocellulose (guncotton), nitrostarch and nitroglycerin. By such chemical processes materials are converted into more powerful explosives than simple gunpowder. Nitroglycerin and nitrocellulose are also mixed with other substances to make dynamite.

3. It has been found that alcohol acting on nitric acid solutions of such metals as copper, silver and mercury forms powerful and very sensitive explosives called fulminates. Fulminate of mercury is largely used in caps as promers or detonators for firing dynamites and other high explosives. Lead hydro nitride (or lead aside) and PETN are used for the same purpose.

4. Explosives are separated into two general classes, low and high. Low explosives like black powder leave about half their volume as a solid residue after explosion and produce a volume of gases that exerts a slow pushing effect on the confining material because of the relatively low rate at which they are generated. High explosives, like nitroglycerin or dynamites, are almost completely gasified when properly initiated and exert a strong shattering effect on the confining walls because of the rapid generation of the gases. The full power of a high explosive may not be realized unless he explosive is properly detonated.

5. Black Powder. The black powder (not commonly used in blasting work at present) is composed of sodium nitrate, charcoal and sulfur in the proportions of about 72, 16 and 12. Because of its low cost, it has a wider sale that blasting powder made with potassium nitrate instead of sodium nitrate. Sodium nitrate has the disadvantage of picking up water, or deliquescing. Powders made from potassium nitrate do not have this disadvantage: consequently they have better keeping qualities. In the manufacture of these black powers, the different ingredients – after being reduced to a fine power – are all ground together while moistened with water. The material is then pressed into cakes which are broken into grains, dried and screened into various sizes ranging from CCC for the coarsest size and FFFF for the finest size.

6. To secure the best results from black powder a hole should be loaded with only one size of grain; then they will all burn at the same speed. The speed with which an explosion will travel along a column of black powder is about 1500 ft. / sec.

7. Judson Powder. This type of explosive, named after its inventor but sold under different trade names, is more powerful than black powder. It is made from a form of black powder in which hard, porous grains are coated with nitroglycerin. These powders are manufactured in several grades containing 50 % of nitroglycerin.

8. The rate of detonation of Judson powder containing 5 % nitroglycerin is some 3300 ft. / sec., or over twice the speed of black powder; the rate of 20 % nitroglycerin is about 8700 ft. / sec. They are not sold to any great extent because the lower grades of dynamite are as effective in their action.

9. Nitroglycerin. This explosive was discovered by Sobrero in 1847 in a laboratory in Paris, but Alfred Nobel in 1863 was the first to manufacture it on a commercial scale. Nitroglycerin is made by mixing sulfuric acid and nitric acid in a steel talk and then adding glycerin. The sulfuric acid takes no chemical part in the reaction but absorbs the water present. To keep the temperature of the reaction within a safe limit, the tank is water jacketed, and coils of lead pipe through which cooling water is circulated are placed inside tank. The nitroglycerin is washed several times with cold water and once with caustic soda to destroy any remaining trace of acid, which affects its keeping qualities.

10. Nitroglycerine is insoluble in water and is poisonous either when in contact with the skin or when breathed as a vapour. It usually produces a violent headache. Ordinary nitroglycerin freezes or becomes crystalline at from 40 to 46⁰ F., but in a recently discovered form it does not freeze even in usual winter temperatures. Being a liquid, nitroglycerin is especially dangerous to handle, since it will leak through a hole in its container. It explodes when heated to about 392⁰ F. It can also be exploded by a violent blow or shock. Although not employed for this purpose extensively at present, its great shattering effect has made it especially suitable for “shooting” oil wells. Because of its sensitiveness to shock, liquid nitroglycerin is dangerous to transport and unsuitable for use in mining and quarrying operations.