Solution

1. Any chemically and physically homogenous 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.

2. 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 particle¹ is of molecular dimensions and that a true solution is formed. On the other hand², very fine sand being mixed with water, a suspension of comparatively large particles, each consisting of many molecules, is obtained. Between these two extremes lie colloidal solutions.

3. From the pharmaceutical stand-point³ solutions of solids in liquids are sure to be of the greatest importance and many quantitative data are available on the properties of such solutions.

4. 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 re-turning to it. The resulting solution is considered to be saturated at the temperature of the experiment.

5. 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.

6. 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 is removed, and the solution is cooled. She 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.

7. To prepare a solution of solids in liquids proper solvents should be available. Water is believed to be the most universally used solvent, since it dissolves both inorganic salts and many organic compounds. Many plant constituents are extracted by water. Alcohol is lively to be the next most useful solvent as it dissolves many organic substances both synthetic and natural, including many important plant constituents. It is often used diluted with water. Water as a solvent in this case should always be used after distillation.

8. Buffer solutions are known to be commonly used in pharmaceutical practice. The standard buffer solutions contain mixtures of a weak acid and its salt and some contain a weak base and its salt. Weak adds or weak bases alone are certain to be poor buffering agents. The most common salts used to prepare standard buffer solutions are acetates, borates, citrates, phosphates and phthalates. Hydrochloric acid buffer solutions, phosphate buffer solutions and alkaline borate buffer solutions are known to be useful in the work of a pharmacist.

ВАРИАНТ 8

1. Перепишите следующие предложения. Определите по грам­матическим признаках, какой частью речи являются слова, оформ­ленные окончанием s, и какую функцию это окончание выполняет.

Переведите предложения на русский язык.

1. The child’s skin is irritated.

2. These bags belong to students.

3. She works as a chemist.

2. Перепишите следующие предложения и переведите их, обра­щая внимание на особенности перевода на русский язык определений, выраженных именем существительным.

1. About one volume of carbon dissolves in one volume of water at room temperature.

2. Take a table spoon of this medicine three times a day for two months.

3. There are three types of drug names well known to all pharmaceutists.