Text f . Nylon

Nylon is a man-made substance which is used both as a fibre for weaving into cloth and in a solid form for such things as combs and gear wheels.

We must take care when we make nylon as some of the chemi­cals which we use are "corrosive", this means that they would burn our skins if we spilt them on ourselves.

Nylon is made by placing two solutions carefully in the same container so that they do not mix but float upon each other. This is rather like cream floating on milk.

The lighter solution should be made by dissolving 4.4 g of methylene in 50 g of water. The heavier solution should be made by dissolving 2 cc of sebacoyl chloride in 100 cc of carbon tetrachloride. Both substances are expensive and corrosive, so great care should be taken.

The carbon tetrachloride + sebacoyl chloride solution should be placed in a200 ml tall-form beaker. The solution of hexamethylene + water should be slowly poured down the side of the same beaker. The two solutions do not mix but where they touch a skin will be seen to have formed. This skin should be pushed aside with tweez­ers and the new skin which then forms can be lifted carefully out and wound around the cotton-reel on the apparatus. The skin forms a kind of "bell-tent" and can be wound out of the beaker by turn­ing the nail handle. The "bell-tent" collapses and forms a continuous thread. This experiment was first carried out in America and was called the "nylon rope trick"!

The thread will go on being formed until all the sebacoyl chlo­ride and hexamine are used up. The thread should now be placed in 50% alcohol in order to wash it. It can then be taken out and dried by leaving it on blotting or filter-paper.

Nylon was first made in America by Dr. W. Carothers in 1938. Nylon has many uses: from making climbing ropes which will sup­port a falling mountaineer to ladies' stockings which are often just called "nylons".

Text g. The carbon cycle

It will now be clear that compounds of the element carbon go through a series of changes in nature which may be repeated over and over again and hence constitute a "cycle". Remember that, al­though matter may change, it can never be destroyed. A given car­bon atom may be found at one time in the atmosphere, at another in the body of a plant, and yet again in the body of an animal.

The absorption of atmospheric carbon dioxide by plants helps to prevent the proportion of this gas in the air from increasing indefi­nitely as it is exhaled by animals. The chief agency, however, which maintains the amount of carbon dioxide in the air at about 3 or 4 parts in 10,000 by volume (0.03-0.04 per cent) is the sea, which dis­solves the gas when the proportion rises above this value, and gives it out when it falls below.

Carbonaceous fuels also play their part in the Carbon Cycle, since they owe their origin ultimately to green plants, and give out carbon dioxide into the air when they are burnt. Petroleum, or min­eral oil, is believed to owe its origin to marine organisms, and hence may be included in the Cycle. We have seen how dissolved carbon dioxide gives rise to calcium hydrocarbonate, which makes water temporarily hard, so that this compound, and the related calcium carbonate, also often of marine origin, play their part in the cycle of changes in which this remarkable element, carbon, plays the principal part.