XI . Answer the questions:

1. What kind of metals are lithium, sodium, potassium and caesium?

2. In what group of the Periodic Classification do these metals fall?

3. When do these metals undergo oxidation rapidly?

4. Why are sodium and potassium compounds of great importance in pharmacy?

5. What compounds are found in comparatively small quantities?

6. What is the chief naturally occurring compound of sodium?

7. How is sodium hydroxide manufactured at present?

TASKS

I. Read and translate the text b: Text b. Proteins and Amino-Acids

Proteins are highly complex compounds elaborated by living cells, and containing the elements of carbon, hydrogen, oxygen, nitrogen, and usually sulphur. They are particularly important as the source of combined nitrogen in foodstuffs. The percentage of nitrogen in most proteins varies from about 15 to 19.

Proteins are classified chiefly according to their solubility; thus albumins are soluble in water while globulins are insoluble in water but soluble in dilute salt solutions. Both albumins and globulins are coagulated by heat. The molecular weights of proteins are known to be estimated only approximately, but investigations by ultracentrifugal methods give results for the soluble proteins varying from a few thousands to many millions. Those proteins which are soluble form colloidal solutions which are generally viscous and may form gels if sufficiently concentrated (e. g. gelatin). From their colloidal solutions many proteins are precipitated by electrolytes. Many of them (e. g. egg albumen) are coagulated by heat. When the temperature is above 60 — 80 °C it produces a marked change in protein structure. This is an example of "denaturation", with diminution in solubility and other changes in properties, which may be brought

about in proteins by various means, including the action of reagents. Substances of such high complexity would not be expected to crystallize under ordinary conditions; nevertheless, some proteins, including egg albumin and hemoglobin, can be obtained in crystalline form by special methods.

Proteins can be hydrolyzed with formation of simpler substances. This process takes place, for example, during digestion in the stomach and intestinal tract.

Amino-acids represent the final stage of protein hydrolysis, and many different amino-acids are produced by the breakdown of a single protein.

The substances intermediate between proteins and amino-acids are not sharply differentiated from one another, since the breaking down process is a gradual one. The progressive decrease in molecular complexity on hydrolysis is accompanied by a corresponding increase in solubility and tendency to crystallization.

Note:

1. the breakdown of a single protein — распад (разложение) белка одного вида

II. Find the equivalents of the words in brackets:

1. Proteins are highly complex compounds (вырабатываемые) by living cells. 2. The percentage of nitrogen in most proteins (варьирует) from about 15 to 19. 3. The molecular weights of proteins can be estimated only (приблизительно). 4. Many proteins are precipitated by (электролитами). 5. The substances intermediate between proteins and amino-acids (не очень резко отличаются) from one another. 6. Proteins can be hydrolyzed (с образованием более простых веществ). 7. Amino-acids (представляют собой) the final stage of protein hydrolysis.