An Elementary Study of Chemistry, William McPherson [icecream ebook reader txt] 📗
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2. Properties. Ethyl alcohol is a colorless liquid with a pleasant odor. It has a density of 0.78 and boils at 78°. It resembles methyl alcohol in its general properties. It is sometimes used as a source of heat, since its flame is very hot and does not deposit carbon, as the flame from oil does. When taken into the system in small quantities it causes intoxication; in larger quantities it acts as a poison. The intoxicating properties of such liquors as beer, wine, and whisky are due to the alcohol present. Beer contains from 2 to 5% of alcohol, wine from 5 to 20%, and whisky about 50%. The ordinary alcohol of the druggist contains 94% of alcohol and 6% of water. When this is boiled with lime and then distilled nearly all the water is removed, the distillate being called absolute alcohol.
Commercial preparation of alcohol. Alcohol is prepared commercially from starch obtained from corn or potatoes. The starch is first converted into a sugar known as maltose, by the action of malt, a substance prepared by moistening barley with water, allowing it to germinate, and then drying it. There is present in the malt a substance known as diastase, which has the property of changing starch into maltose. This sugar, like glucose, breaks down into alcohol and carbon dioxide in the presence of yeast. The resulting alcohol is separated by fractional distillation.
Denatured alcohol. The 94% alcohol is prepared at present at a cost of about 35 cents per gallon, which is about half the cost of the preparation of methyl alcohol. The government, however, imposes a tax on all ethyl alcohol which amounts to $2.08 per gallon on the 94% product. This increases its cost to such an extent that it is not economical to use it for many purposes for which it is adapted, such as a solvent in the preparation of paints and varnishes and as a material for the preparation of many important organic compounds. By an act of Congress in 1906, the tax was removed from denatured alcohol, that is alcohol mixed with some substance which renders it unfit for the purposes of a beverage but will not impair its use for manufacturing purposes. Some of the European countries have similar laws. The substances ordinarily used to denature alcohol are wood alcohol and pyridine, the latter compound having a very offensive odor.
Fermentation. The reaction which takes place in the preparation of ethyl alcohol belongs to the class of changes known under the general name of fermentation. Thus we say that the yeast causes the glucose to ferment, and the process is known as alcoholic fermentation. There are many kinds of fermentations, and each is thought to be due to the presence of a definite substance known as an enzyme, which acts by catalysis. In many cases, as in alcoholic fermentation, the change is brought about by the action of minute forms of life. These probably secrete the enzymes which cause the fermentation to take place. Thus the yeast plant is supposed to bring about alcoholic fermentation by secreting the enzyme known as zymase.
Glycerin (C3H5(OH)3). This compound may be regarded as derived from propane (C3H8) by displacing three atoms of hydrogen by three hydroxyl groups, and must therefore be regarded as an alcohol. It is formed in the manufacture of soaps, as will be explained later. It is an oily, colorless liquid having a sweetish taste. It is used in medicine and in the manufacture of the explosives nitroglycerin and dynamite.
ALDEHYDESWhen alcohols are treated with certain oxidizing agents two hydrogen atoms are removed from each molecule of the alcohol. The resulting compounds are known as aldehydes. The relation of the aldehydes derived from methyl and ethyl alcohol to the alcohols themselves may be shown as follows:
The first of these (CH2O) is a gas known as formaldehyde. Its aqueous solution is largely used as an antiseptic and disinfectant under the name of formalin. Acetaldehyde (C2H4O) is a liquid boiling at 21°.
ACIDSLike the other classes of organic compounds, the organic acids may be arranged in homologous series. One of the most important of these series is the fatty-acid series, the name having been given to it because the derivatives of certain of its members are constituents of the fats. Some of the most important members of the series are given in the following table. They are all monobasic, and this fact is expressed in the formulas by separating the replaceable hydrogen atom from the rest of the molecule:
Formic acid (H·CHO2). The name "formic" is derived from the Latin formica, signifying ant. This name was given to the acid because it was formerly obtained from a certain kind of ants. It is a colorless liquid and occurs in many plants such as the stinging nettles. The inflammation caused by the sting of the bee is due to formic acid.
Acetic acid (H·C2H3O2). Acetic acid is the acid present in vinegar, the sour taste being due to it. It can be prepared by either of the following methods.
1. Acetic fermentation. This consists in the change of alcohol into acetic acid through the agency of a minute organism commonly called mother of vinegar. The change is represented by the following equation:
The various kinds of vinegars are all made by this process. In the manufacture of cider vinegar the sugar present in the cider first undergoes alcoholic fermentation; the resulting alcohol then undergoes acetic fermentation. The amount of acetic acid present in vinegars varies from 3 to 6%.
2. From the distillation of wood. The liquid obtained by heating wood in the absence of air contains a large amount of acetic acid, and this can be separated readily in a pure state. This is the most economical method for the preparation of the concentrated acid.
Acetic acid is a colorless liquid and has a strong pungent odor. Many of its salts are well-known compounds. Lead acetate (Pb(C2H3O2)2) is the ordinary sugar of lead. Sodium acetate (NaC2H3O2) is a white solid largely used in making chemical analyses. Copper acetate (Cu(C2H3O2)2) is a blue solid. When copper is acted upon by acetic acid in the presence of air a green basic acetate of copper is formed. This is commonly known as verdigris. All acetates are soluble in water.
Butyric acid (H·C4H7O2). Derivatives of butyric acid are present in butter and impart to it its characteristic flavor.
Palmitic and stearic acids. Ordinary fats consist principally of derivatives of palmitic and stearic acids. When the fats are heated with sodium hydroxide the sodium salts of these acids are formed. If hydrochloric acid is added to a solution of the sodium salts, the free palmitic and stearic acids are precipitated. They are white solids, insoluble in water. Stearic acid is often used in making candles.
Acids belonging to other series. In addition to members of the fatty-acid series, mention may be made of the following well-known acids.
Oxalic acid (H2C2O4). This is a white solid which occurs in nature in many plants, such as the sorrels. Its ammonium salt ((NH4)2C2O4) is used as a reagent for the detection of calcium. When added to a solution of a calcium compound the white, insoluble calcium oxalate (CaC2O4) precipitates.
Tartaric acid (H2·C4H4O6). This compound occurs either in a free state or in the form of its salts in many fruits. The potassium acid salt (KHC4H4O6) occurs in the juice of grapes. When the juice ferments in the manufacture of wine, this salt, being insoluble in alcohol, separates out on the sides of the cask and in this form is known as argol. This is more or less colored by the coloring matter of the grape. When purified it forms a white solid and is sold under the name of cream of tartar. The following are also well-known salts of tartaric acid: potassium sodium tartrate (Rochelle salt) (KNaC4H4O6), potassium antimonyl tartrate (tartar emetic) (KSbOC4H4O6).
Cream of tartar baking powders. The so-called cream of tartar baking powders consist of a mixture of cream of tartar, bicarbonate of soda, and some starch or flour. When water is added to this mixture the cream of tartar slowly acts upon the soda present liberating carbon dioxide in accordance with the following equation:
KHC4H4O6 + NaHCO3 = KNaC4H4O6 + H2O + CO2.
The carbon dioxide evolved escapes through the dough, thus making it light and porous.
Citric acid (H3·C6H5O7). This acid occurs in many fruits, especially in lemons. It is a white solid, soluble in water, and is often used as a substitute for lemons in making lemonade.
Lactic acid (H·C3H5O3). This is a liquid which is formed in the souring of milk.
Oleic acid (H·C18H33O2). The derivatives of this acid constitute the principal part of many oils and liquid fats. The acid itself is an oily liquid.
ETHEREAL SALTSWhen acids are brought in contact with alcohols under certain conditions a reaction takes place similar to that which takes place between acids and bases. The following equations will serve as illustrations:
The resulting compounds of which methyl nitrate (CH3NO3) may be taken as the type belong to the class known as ethereal salts, the name having been given them because some of them possess pleasant ethereal odors. It will be seen that the ethereal salts differ from ordinary salts in that they contain a hydrocarbon radical, such as CH3, C2H5, C3H5, in place of a metal.
The nitrates of glycerin (nitroglycerin). Nitric acid reacts with glycerin in the same way that it reacts with a base containing three hydroxyl groups such as Fe(OH)3:
The resulting nitrate (C3H5(NO3)3) is the main constituent of nitroglycerin, a slightly yellowish oil characterized by its explosive properties. Dynamite consists of porous earth which has absorbed nitroglycerin, and its strength depends on the amount present. It is used much more largely than nitroglycerin itself, since it does not explode so readily by concussion and hence can be transported with safety.
The fats. These are largely mixtures of the ethereal salts known respectively as olein, palmitin, and stearin. These salts may be regarded as derived from oleic, palmitic, and stearic acids respectively, by replacing the hydrogen of the acid with the glycerin radical C3H5. Since this radical is trivalent and oleic, palmitic, and stearic acids contain only one replaceable hydrogen atom to the molecule, it is evident that three molecules of each acid must enter into each molecule of the ethereal salt. The formulas for the acids and the ethereal salts derived from each are as follows:
Olein is a liquid and is the main constituent of liquid fats. Palmitin and stearin are solids.
Butter fat and oleomargarine.
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