Ex.11Відкрийте дужки, підбираючи необхідне слово

1. (A balance, a calorimeter, a thermometer) is a device which determines the quantity, but not the quality of heat in a body. 2. If a chemist determines mass, he is to employ (a flask, a thermometer, a balance). 3. (A calorimeter, a flask, a microscope) is used if a chemist must examine small samples of matter. 4. For the measurement of volumes of gases a chem­ist uses (burettes, pipettes, gas burettes). 5. The unit of (volume, mass) in the metric system is the gram. 6. On (the Centigrade scale, the Fahrenheit scale) the freezing point of water is 0°. 7. If a chemist must measure extremely short dis­tances, (the centimetre, the micron) is to be used

Ex. 12Прочитайте, перекладіть текст.

A thermometer is a device which is used to determine the temperature of a body. Two bodies of unequal size may have the same temperature; the bigger contains more heat, but the quality of the heat in each is the same. Thermometers take many forms, the commonest of which is the mercury-bulb variety.

There are two scales—Centigrade and Fahrenheit.

On the Fahrenheit scale the freezing point of water is marked as 32° and the boiling point of water as 212°. On the Centigrade scale the freezing point of water is called 0° and its boiling point 100° (see Fig. 5). Thus, 130 divisions on the Fahrenheit scale are equal to 100 divisions on the Centigrade scale,

and 1°F=5/9°C.

If the chemist wants to convert temperatures from one scale to the other, the following formulas are to be used: C = 5/9(F — 32) andF-9/5C + 32

Ex. 13. Прочитайте, перекладіть текст. Дайте відповіді на питання.

The Balance

If the chemist is to determine mass, he should use a balance. The balance is an instrument which is used when it is necessary to compare known masses with unknown masses Some balances are much more sensitive than others, that is, some can detect smaller differences in mass than others. This sensitivity depends upon several factors. In the first place, the sensitivity increases as the length of the beam increases, and secondly, the sensitivity increases as the mass of the object on the pan increases. Thirdly, the sensitivity increases as the weight of the beam decreases.

In the average chemical laboratory there are usually three types of balances. The analytical balance is the most sensitive. It is kept in a glass case, in a special balance room, where the temperature is constant. Hot or cold objects shouldn't be placed on such a balance and the glass case should be closed.

1. When is the chemist to use a balance?

2. What is a balance?

3. Which balance is the most sensitive?

4. Where is the analytical balance to be kept?

Ex. 14 Прочитайте, перекладіть текст

Very often a chemist has to measure volumes of liquids. The commonest instrument is the graduated cylinder. On the side of it one can see scratches. They correspond to millilitres. The cylinder has a lip so that its contents may be poured easi­ly into another container.

The volumetric flask is used for the preparation.of solutions.

The burette and the pipette are used in quantitative analysis and other quantitative work. The burette is a glass tube, open at the top end. The pipette has a scratch on the neck. This scratch is the mark to which it can be filled.

Ex. 15. Прочитайте, перекладіть текст

The chemical industry needs instruments for accurate measuring. Good measuring instruments are able to give rapid results. Without modern instrumentation chemical processes were often controlled by a human operator who had to decide what needed to be done, It was rather difficult to do. The results had often to be checked thoroughly. There are many different kinds of measuring instruments and -there is much information about the instruments which are to be used in chemical plants. The purpose of all measuring devices is to control a chemical reaction. In a process controlled by a human operator, the temperature, for example, can be read from a thermometer. The operator is to decide whether the temperature is all right. Then he has to make some measurements. In the automated system, some mechanical or electrical device must replace the human operator to decide whether a process correction is needed and, if so the extent of the necessary correction.