XI. Прочитайте и переведите текст А
Text A. Solution
Any chemically and physically homogeneous mixture of two or more substances is said to be a solution. It is possible to have solutions of solids in liquids, liquids in liquids, gases in liquids, solids in solids, etc.
Depending upon the size of the dispersed particles we recognize true solutions, colloidal solutions, and suspensions.
If sugar is dissolved in water, it is supposed that the ultimate sugar particle ' is of molecular dimensions and that a true solution is formed. On the other hand if very fine sand is mixed with water, a suspension of comparatively large particles, each consisting of many molecules is obtained. Between these two extremes lie colloidal solutions.
From the pharmaceutical stand-point solutions of solids in liquids are of the greatest importance and many quantitative data are available on the properties of such solutions.
When an excess of a solid is brought into contact with a liquid, molecules of the former are removed from its surface until equilibrium is established between the molecules leaving the solid and those returning to it. The resulting solution is said to be saturated at the temperature of the experiment.
The extent of solubility of different substances varies from almost imperceptible amounts to relatively large quantities but for any given solute the solubility has a constant value at constant temperature.
Under certain conditions it is possible to prepare a solution containing a larger amount of solute than is necessary to form a saturated solution. This may occur when a solution is saturated at one temperature, the excess of solid solute removed, and the solution cooled. The solute present in solution, even though it may be less soluble at a lower temperature, does not always separate from the solution and a supersaturated solution is produced.
Words:
ultimate sugar particle — элементарная частица сахара
on the other hand — с другой стороны
under certain conditions — при определенных условиях
TASKS
I. Find the following equivalents in the text:
1.степень растворимости различных веществ 2. с другой стороны 3. количественные данные 4. взвешенные частички 5. истинный раствор 6. элементарная частица сахара 7. взвесь сравнительно больших частичек 8. избыток твердого растворенного вещества 9. растворы твердых частиц в жидкостях 10. растворенное вещество, находящееся в растворе.
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II. Answer the questions:
1. What mixtures may be defined as a solution?
2. Is it possible to obtain a solution only by dissolving solids in liquids?
3. What kinds of solutions are recognized?
4. What does the variety of a solution depend upon?
5. What is very fine sand mixed with if we want to obtain a suspension?
6. Is much known about the formation of colloidal solutions?
7. Why are many quantitative data available on the properties of solutions of solids in liquids?
8. How does the extent of solubility of different substances vary?
III. Complete the following sentences according to the text:
1. Depending upon the size of the dispersed particles we recognize… .
2. … these two extremes lie colloidal solutions.
3. From the pharmaceutical stand-point solutions of solids in liquids are of the greatest importance and many quantitative data …
4. … is said to be saturated at the temperature of the experiment.
5. Under certain conditions it is possible to prepare a solution containing a larger amount of solute than is necessary … .
6. … when a solution is saturated at one temperature,
IV. Read and translate the following text:
Text B. Ointments
Ointments are semi-solid preparations for external application of such consistency that they may be readily applied to the body or to mucous membranes.
They should be of such composition that they soften but not necessarily melt when applied to the body.
The ointment base1 usually constitutes the major portion of the pharmaceutical preparation and, therefore, may influence the efficacy of the incorporated medicinal substances.
Based on their penetration ointments have been divided into three classes. Epidermic ointments are those which demonstrate no, or very slight, power of penetration into the skin. The bases which contain petrolatum, waxes and their combinations have been placed in this group.
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Endodermic ointments are those which possess some power of penetration into the deeper layers of the skin. Most of them have a somewhat lower melting point, approaching the temperature of the skin, and contain vegetable oils, lard, wool fat, lanolin, and/or combinations of these.
Diadermic ointments are those which penetrate the skin, thus offering a better opportunity for absorption of the medicament. Ointments of emulsion type and the water-soluble bases belong to the group of absorption base.
Hydrocarbon bases include ointments prepared from petrolatum, or liquid petrolatum, with wax or other stiffening agents.
White and yellow ointments are relatively stable to normal climatic temperature changes. Absorption bases generally have a high index of compatibility toward the majority of medicaments used topically. These bases have found a definite place in pharmacy as well as cosmetology.
Until recently, ointments and ointment type products were packaged in glass, stoneware, porcelain, polyethylene, or plastic wide-mouth jars. Since a large area of the ointment was exposed to the effects of air, those ointments containing easily oxidized medicinals were packaged in collapsible metal tubes. The use of aerosol containers preventing contamination, drying out of the product as well as protecting water sensitive drugs is preferable.
Words:
ointment base – мазевая основа; absorption base –быстро и полностью всасывающаяся основа; wide – mouth jars –сосуды с широкими горлышками
V. Fill in the proper words from the text:
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