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The Manufacture of Sulphuric Acid

Free Radicals

An atom or group of atoms with one or more unshared electrons, which may enter into chemical-bond formation is called a free radical. Free radicals are usually highly reactive and difficult to prepare in any except low concentration. One way of making the methyl radical as a dilute gas is by heating mercury dimethyl, which decomposes to give metallic mercury and methyl radical. Methyl radical can also be made conveniently by the decomposition of diacetyl, by either heat or ultraviolet light. The diacetyl molecule liberates two molecules of carbon dioxide and two methyl radicals. The American chemist Moses Comberg discovered in 1900 that some hydrocarbon free radicals are stable. He attempted to synthesize the substance, which he expected to be a stable, white, crystalline substance. Instead he obtained a strongly coloured solution containing the stable free radical tryhenylmethyl.

 

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The Manufacture of Sulphuric Acid

It is a matter of common knowledge among chemists that sulphuric acid is made by two processes, the contact process and the lead-chamber process, which are now about equally important. In the contact process sulphur trioxide is made by the catalytic oxidation of sulphur dioxide. The catalysts formerly used was finely divided platinum; it has now been largely replaced by vanadium pentoxide. The gas containing sulphur trioxide is then bubbled through sulphuric acid, which absorbs the sulphur trioxide. Water is added at a proper rate, and 98% acid is drawn off. In the lead-chamber process oxygen, sulphur dioxide, nitric oxide, and a small amount of water vapour are introduced into a large lead-lined chamber. White crystals of nitrosulphuric acid are formed. When steam is introduced the crystals react to form sulphiric acid, liberating oxides of nitrogen.

 

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Radiation Effects on Polymers

Radiation exerts two opposing effects on polymers. On the one hand, it breaks up the polymer molecules into smaller pieces. On the other, it causes liberation of a hydrogen atom from each of the two adjoining molecules with formation of a link between the two molecules. The existence of cross-links in a polymer makes the material tougher and higher melting and is very desirable for certain applications. The cross-linking of polymers by radiation has been much studied. The irradiation of any organic compounds resulting in breaking of CH bonds, leaving free bonds on the carbon atoms while the hydrogen atoms go off together in pairs to form hydrogen gas. In a liquid the resulting free radicals can diffuse as a whole through the solution and eventually meet together and combine. In a solid polymer it is not clear how these centres get together. Whatever the mechanism of cross-linking may be the result is of commercial value.

 

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A Brief History of Polypeptide Chemistry

Protein chemistry really began in 1830s with Mulder’s systematic investigation of nitrogenous biological materials such as blood fibrin, egg white, gelatins, and silk. In 1840 Hunefeld was the first to crystallize a protein. During the following 90 years, amino acids, the building blocks of protein, were isolated by many investigators. But for many years it was not realized how amino acids were linked to form proteins. In 1902 two German chemists independently proposed that amino acids were joined together by peptide bonds. In 1926 Sumner made a tremendous advance when he recognized that enzymes were, in fact, proteins. He came to this conclusion after he has successfully crystallized a protein that was associated with enzymatic activity. He noticed that the degree of degradation of this highlypurified protein could be correlated with the disappearance of the associated enzymatic activity.

 

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Conductance and Electrolysis

Generally speaking, the classification of a substance as a non-electrolyte or as an electrolyte is based on the conductance of it aqueous solution. Aqueous solutions of non-electrolytes do not conduct electric current to any greater extent than pure water does. Aqueous solutions of electrolytes conduct an electric current and undergo electrolysis. Weak electrolytes give solutions which are relatively poor conductors because of a limited degree of ionization. On the other hand, aqueous solutions of strong electrolytes readily conduct an electric current. If a strong electrolyte is formed as a result of a chemical reaction involving two weak electrolytes the conductance of a resulting solution increases. If the ions of a strong electrolyte are removed from solution as an insoluble precipitate, the conductance of a mixture of the reactants is less than that of a strong electrolyte.

 

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A Metal that Doesn’t Sink

A little plate of greyish metal was as light as a chip of wood and didn’t sink in water. It was a sample of magnesium-lithium alloy developed at the Metallurgy Institute of the USSR Academy of Sciences. Silver-white magnesium is lighter than aluminum and superior to it in heat capacity and in its capability to act as the main component of various structural materials. It is, in fact, 1.5 times lighter than aluminum and 4.5 times lighter than iron. It doesn’t give off sparks from friction or on being stuck, and is easy to work or weld with, electrically or using gas. Magnesium is also one of the most widespread metals. Its resources are dozens of time higher than those of nickel, zinc, and lead. As for lithium, the third element in the Mendeleyev periodic table, it is the lightest of all metals. Everything new and unusual appearing today in metallurgy, chemistry and power-engeneering is to a large extent connected with lithium.

 

 

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Insulator Turns Into Superconductor

Having used ultrahigh pressures and critically low temperatures, scientists at the Institute of High Pressures of the USSR Academy of Sciences have managed to effect such a unique transformation as converting a sulphur insulator into a superconductor. Superconductivity, at which a conductor completely lacks resistance to electric current, was discovered more than 70 years ago. Present-day electronic, electrotechnical apparatuses, instruments and macines have been developed, operating on superconductors under conditions of low temperatures. Among them are radio-receiving devices for detecting weak signals arriving from the depths of outer space, highly efficient powerful, and yet small current generators, transformers and cables. Scientists are looking for materials which would become superconducting at a temperature of, for example, liquid hydrogen, or liquid nitrogen. Sulphur has been quite unexpectedly found among the superconducting materials.

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Boiling process

Experimental measurements show that the equilibrium vapour pressure of a liquid increases as the temperature increases. The temperature at which the equilibrium vapour pressure becomes equal to 1 atm is called the normal boiling temperature, or the boiling point. In the boiling process, bubbles of vapour form throughout the bulk of the liquid. In other words, evaporation occurs anywhere in the liquid, not just at the upper surface. The initiation of a bubble in the bulk of a pure liquid is a very difficult process, since it requires that many molecules with kinetic energies greater than that required for vaporization must be close to one another. The fact that the liquid reaches the boiling temperature is no guarantee that boiling will occur. If it doesn’t, continued addition of heat will cause the liquid to become superheated, that is, to reach a temperature greater than its boiling point.

 

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Modern Methods of Analysis

The so-called classical gravimetric and volumetric methods have been superseded by physical chemistry and physical methods. But instrumental analysis, as it is known today, supplements rather than supplants the so-called classical wet method. Such terms as calorimetry, spectrophotometry, fluorimetry, spectrography, X-ray diffracation, radiometric methods, polarography are in common usage. Every part of the analytical work is now performed through the use of the instrumentation. Indeed, modifications of many of these instruments are moved out into actual manufacturing operations in order to provide continuous analysis. One of the modern developments in the field of analysis is that of microanalysis. The determination of very low concentration is often of great importance in maintaining high quality of a product. A wide variety of new techniques have been developed to meet this need.

 

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The Properties of Solutions

It is difficult to give a definition which tells clearly and briefly how solutions differ from mixtures and compounds. A solution is a homogeneous substance that has a continuously variable composition. The word “homogeneous” sets a true solution apart from a mechanical mixture. Mixtures have macroscopic regions which have distinct and different composition and properties. The properties and composition of a solution are uniform, as long as a solution is not examined at the molecular level. There are substances, however, not to be clearly classified as solutions or mixtures. A solution of soap in water has a cloudy appearance due to particles which consist of many soap molecules collected together. Such a substance has properties and composition which might be described as either inhomogeneous or homogeneous depending on the experiment to be done. Therefore there is no sharp dividing line between mixtures and solutions.

 

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Free Radicals

An atom or group of atoms with one or more unshared electrons, which may enter into chemical-bond formation is called a free radical. Free radicals are usually highly reactive and difficult to prepare in any except low concentration. One way of making the methyl radical as a dilute gas is by heating mercury dimethyl, which decomposes to give metallic mercury and methyl radical. Methyl radical can also be made conveniently by the decomposition of diacetyl, by either heat or ultraviolet light. The diacetyl molecule liberates two molecules of carbon dioxide and two methyl radicals. The American chemist Moses Comberg discovered in 1900 that some hydrocarbon free radicals are stable. He attempted to synthesize the substance, which he expected to be a stable, white, crystalline substance. Instead he obtained a strongly coloured solution containing the stable free radical tryhenylmethyl.

 

Text 12

The Manufacture of Sulphuric Acid

It is a matter of common knowledge among chemists that sulphuric acid is made by two processes, the contact process and the lead-chamber process, which are now about equally important. In the contact process sulphur trioxide is made by the catalytic oxidation of sulphur dioxide. The catalysts formerly used was finely divided platinum; it has now been largely replaced by vanadium pentoxide. The gas containing sulphur trioxide is then bubbled through sulphuric acid, which absorbs the sulphur trioxide. Water is added at a proper rate, and 98% acid is drawn off. In the lead-chamber process oxygen, sulphur dioxide, nitric oxide, and a small amount of water vapour are introduced into a large lead-lined chamber. White crystals of nitrosulphuric acid are formed. When steam is introduced the crystals react to form sulphiric acid, liberating oxides of nitrogen.

 

 






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