Notes on the Text

1. on the other hand — с другой стороны

2. none of — ни один из

3. so long as — пока

4. a true solution — истинный раствор

Text. Colloids and colloidal particles

If one shook sand and water together in a closed vessel a momentary suspension of the sand particles in the water would be obtained. As soon as the agitation ceases, however, the sand particles begin to settle to the bottom of the vessel, where in a very short time, nearly all of them collect, leaving a clear supernatant liquid above.

If on the other hand one shook sugar and water together, a homogeneous mixture would be formed from which none of the solute would tend to settle, so long as there were suffi­cient water present to maintain the mixture. The former of _: these systems could be referred to as a coarse suspension, the latter as the solution, intermediate between systems of these two types being a third type of dispersion. The particles of this middle class, when suspended, are too small. They couldn’t be seen with the aid of the best of optical microscopes. They are so small that they could not be caught by the most fine filter paper, and they do not settle to the bottom of the vessel. These particles when suspended in a liquid do not tend to diffuse into an adjoining layer of the pure dispersing liquid.

It was Thomas Graham who made a careful study of such particles. He suggested that they should be named “colloid”. ■ The term “colloid” is derived from “kolla”, the Greek word for glue. ¹

Today the terms “colloid”, “colloidal” do not refer to def- inite categories of matter, but rather to particles of any ,: variety of matter whose dimensions lie within a certain range, ;

>•: 11

The smallest particles in the coarse suspension might have , a length of about 5x 10"* cm, while particles whose length, ^:

or diameter, is 1X 10”⁷ cm or less might have all the charac­teristic behaviour of the particles which constitute a true solution.

Hence, the colloidal particles lie between 1 x 10^-7 and 5x 10~§ cm.

This range is purely arbitrary.

A substance which is dispersed in particles of colloidal size throughout another might be called the dispersed or internal phase of the mixture, while the second component is known as the dispersion medium or the external phase. If a solid were colloidally dispersed in a liquid, it could be referred to as a suspensoid, while a liquid colloidally dis­persed in a second liquid could often be referred to as an emulsoid.

Since each of the three states of matter might be suspended colloidally in matter of each of the three states, it might be anticipated that there would be nine types of colloidal dis­persions; actually there are only eight, for mixtures of gases, because of the relatively large distances between their mole­cules, form only true solutions.

Remember the following words and word combinations:

to shake (shook,	so long as	dimension
shaken)	to maintain	length
agitation	coarse	to lengthen
to cease	suspended	arbitrary
to settle	aid	to disperse
solute	to catch (caught,	dispersion
long	caught)	internal
any longer	fine	medium
no longer	to adjoin	to anticipate

Ex. 11. Remember the following word combinations:

as soon as — как только only true solution—только

with the aid of—с помощью истинный раствор within range—в пределах the only true solution—един­ственно истинный раствор

Ex. 12. Answer the following questions:

1. When can a momentary suspension be obtained? 2. What happens when the agitation ceases? 3. What happens if sugar and water are shaken together? 4. What is the third type of

dispersion? 5. Is it possible to see the particles of the middle class? 6. Why is it impossible to see these particles? 7. What does the term “colloid” refer to? 8. What is a dispersed phase?

Ex. 13. Choose the Russian equivalents from the right column:

at least suddenly at last as long as long before to tend variety

пока

задолго до стремиться разнообразие внезапно по крайней мере наконец

Ех. 14. Open the brackets choosing the suitable word:

1. Don’t look at him so (closely, close). 2. You have (closed, close) the laboratory, haven’t you? 3. the future ol automation is (close, closely) linked with cybernetics. 4. The rate of reaction is accelerated (as long as, any longer) uni­form heating is used. 5. If we shake sand and water together in a (closed, closely) vessel, a momentary suspension will be obtained. 6. I can’t stay in this laboratory (any longer, no longer).

Ex. 15. Complete the sentences choosing the suitable word from the list of the words given below:

1. Very . . . particles of substances which have little ability to absorb light scatter blue light more than they do red light. 2. ... particles are not so affected because their surfaces are very large. 3. Colloidal particles are small enough to pass through a filter paper, they do not ... to the bottom. 4. Nearly all suspended colloidal particles are elec­trically . . ., as is shown by the fact that they can travel toward one pole or the other of an electrolytic cell. 5. If two sols whose particles have . . . charges are mixed in equal proportions, precipitation of the dispersed phases takes place. 6. If you shake water and sugar in a closed vessel a . . . mixture will be formed. 7. These particles are too . . . to be seen under this microscope. 8. A substance which is dispersed in particles of colloidal size throughout another is called the . . . phase of the mixture.

fine, coarse, to settle, to rise, charged, discharge, unlike like, homogeneous, heterogeneous, small, large, internal, external.

Бх. 16. Complete the sentences:

1. A suspension of sand particles would have taken place

If one 2. If the agitation ceased, the sand particles

3. A homogeneous mixture could be formed if one

.... 4. If a solid were colloidally dispersed in a liquid, it • .... 5. If you had read this text attentively, you . . . -

6. Were this text not so difficult, we ... .

Ex. 17. Translate the sentences paying attention to the meanings of

“would”:

1. Thus, theoretically, a given sample would never entire­ly disappear. 2. Since silicon shows a valence of four, it would naturally be expected to form the hydroxide Si(OH)₄.

3. It would seem from this description that most of the in­terior of an atom is empty space, similar to that between the planets and the sun. 4. The idea occurred to Fermi that neutrons would be produced during the fission process. 5. The dual behaviour of dilute solutions of hydrogen peroxide would have been predicted from the fact that the oxidation number of oxygen in H₂0₂ is —1. 6. Under various influences atoms combine in exact proportions to form compounds, just as Dalton has said they would. 7. Rutherford was the first to see that if a suitable nuclear projectile were available, it might be possible to bring it into such powerful contact with another nucleus that a proton would be ejected. 8. The scientist said that it would be necessary to tell about ioni­zation in order to clarify the theory of the electromagnetic method. 9. It would be very difficult to carry out this re­search without electronic equipment. 10. They would repeat their experiment many times if the results were unsatis­factory. 11. Unless the atmosphere contained oxygen, nei­ther life nor burning would be possible. 12. The absolute zero of temperature would represent the cessation of mo­lecular motion.

Ex. 18. Translate the sentences paying attention to the meanings of

“should”:

1. It should be mentioned that the gamma rays of radium are of shorter wave length than any other form of radiant energy could be. 2. It is necessary that the solution should be dried. 3. If the experiment hadn’t been so time-consum^ ing, we should have been able to complete it much earlier.

3. Before beginning our work we should like to check all the (lata received. 5. In each case this question should be consid­ered separately. 6. An indicator should actually change co­lour when acid and base are brought together in chemically equivalent quantities. 7. If the titration were continued until the solution became neutral, we should have too much acid.

8. The scientist suggested that this lecture should be devoted to the latest discoveries in the field of inorganic chemistry.

9. Decrease the temperature lest the solution should be evap­orated. 10. Switch off the device lest it should be overheat­ed. 11. It is necessary that the battery should be charged.

12. It is surprising that this process should continue. 13. It is necessary that synthetic dyes, perfumes and medicines should be widely used instead of the natural substances.

Ex. 19. Read the following and give a summary of it:

When dissolved substance is in the molecular or ionic state a solution is homogeneous.

Solute particles diffuse readily into a layer of the pure solvent. Finally divided solids produce suspensions when they are shaken with a liquid in which they are not soluble.

In a coarse suspension the particles of the solid are vis­ible to the unaided eye. There is an intermediate range be­tween the solution and the mechanical mixture, in which the dispersed material retains its former phase, but the parti­cles are so small that they are not visible. Such systems are called dispersed systems.

A colloidal system is a heterogeneous system in which the dispersed material is distributed uniformly in a fine state throughout the dispersing medium.

Ex. 20. Translate the text paying attention to the Adverbial Clauses of Condition:

If colloidly dispersed particles in liquid systems could pass through filter paper, they would not separate from the liquid.

The most noticeable differences in properties between colloidal dispersions and coarser suspensions are due to the fine state of the colloidal particles. The more finely divided the substances are, the greater the number of particles and the total area of the surface exposed for the same weight of material.

The total surface of a cube with 1cm edges is 6sq cm. If this cube were cut in half along each of its three dimen­sions, there would be eight cubes, with 1/2 cm edges, and the total surface would be 12 sq cm.

If this process of subdivision were continued to the lower limits of colloidal size, the total surface area would be approx­imately 1*4 acres.

Ex. 21. Read the text and retell it (use Fig. 8):

Electric Charges of the Particles in Colloidal Suspension

Fig. 8.

Colloidally dispersed particles almost always carry an electric charge. This may be shown by placing a colloidal suspension beneath water in a large i/-tube (see Fig.-8) and inserting electrodes connect­ed with a source of direct current into the clear liquid. If colloidal arsenious sulphide were tested in this manner, it would be found that the colloidal particles would move toward the anode, bearing negative charges in general. Many of the metal sulphides and the free noble metals form negatively charged particles in the colloidal state.

The source of this charge cannot be stated with certainty, though it is fprobably due to the adsorption of specific electrically charged ions from the solution. The charges of the colloidal particles are balanced by the charges of free ion in the solution.