A comparison of a few points of the Centigrade and Fahrenheit scales

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) 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) and F=9/5C.+32.

2. Translate the text and answer the questions that follow. 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?

3. Read and retell the text.

Very often the 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 milliliters. 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.

Unit V.

The general apparatus of inorganic laboratory Part a

1. Learn the following words.

to carry out – производить, выполнять

to carry out an experiment

to affect – воздействовать, влиять

to clamp – закреплять (зд. Зажим

to fit - устанавливать

to furnish – снабжать, обставлять (мебелью)

to keep – держать, хранить

to pour – лить, наливать

to purify – очищать

to store – хранить

to suspend – вешать, подвешивать

to swing - качаться

to weigh – взвешивать

to yield – давть, производить

balance – весы

beam – коромысло (весов)

bowl – чаша

burner – горелка

case - ящик

crucible – тигель

disturbance – неблагоприятное воздействие

edge – край

flask – фляжка, колба, бутыль

gauze – металлическая сетка

odour – запах

pan – чашка

rack – полка, стеллаж

ring-stand – штатив

rod – палочка

shelf – полка (shelves – стеллаж)

stem – стержень

tap – кран

tube - трубка

test-tube – пробирка

vapour – пар, пары, испарения

ventilating hood – вентиляция

firm – твердый, устойчивый, прочный

external – внешний

so as – так, таким образом

2. Remember plural forms of the following words.