Nowadays a higher proportion of people than ever before live in well-built houses, have enough to eat, are well clothed and have at birth an expectation of life of some Sixty to seventy years. Two centuries ago this expectation ot life was not much
more than half the present figure, for lack of medical knowledge together with poor living conditions resulted in much ill health and in epidemics which wiped out huge
sections of the population at a single stroke.
Science has changed all this-through researches in medicine and agriculture, by finding ways to make the things we need more rapidly and more cheaply and by discovering new substances out of which we can construct the complicated machinery of the modern world.
Here are some of the techniques developed by science in the
past two centuries.
Brick-making by Machine
Most countries have clay suitable for brick-making. This is dug out of the ground by mechanical shovels, then fed intoa
system of huge rollers which crush it into a fine, powdery substance. Moisture is added, and a band of clay is forced through a hole and then cut into individual bricks by wires.
The wet bricks are slowly dried, then put in a kiln and baked at a high temperature.
Modern building technique is very 1largely dependent on cement. Clay, chalk and limestone are crushed, then fed into a
machine which mixes them with water into a thick cream. This cream, known as ‘slurry’, is conveyed to a high-temperaturekiln which reduces it to clinker. The clinker passes between a series of rollers which grind it up, and the pale grey powder
which results is cement. For building purposes this is mixed in a revolving drum with sand and water, using proportions of
from three to five shovels of sand to each shovel of cement.
For concrete, up to six shovels of ‘aggregate’ (a mixture of
sand and small stones) is used with each shovel of cement.
This is produced by using water power, some form of fuel, or atomic energy (see section on Nuclear Power). The pressure of water from a dam, or, alternatively, steam created by burning fuel, turns a dynamo. The rotation of this spins a rotor. The rotor is an electro-magnet, which, surrounded by a coil of wire, sets up an electric current in the wire.
Still the principal source of heat for household cooking, gas is
made by baking coal in a container or retort. The gas given off is stored in gasometers until required. By-products of the
process include petrol, acids, drugs, perfumes, dyes, tar and coke. Natural gas from the North Sea is being used in Britain
for commercial and domestic purposes.
The method of glass manufacture has changed little over the centuries, but the speed and mechanisation have been greatly
increased. Specially selected sand is mixed with limestone and soda ash and melted until liquid. It is then rolled out to make
plate glass, moulded to make the cheaper kind of jars, tumblers and bottles, or blown into shape for high-quality articles. Glass-blowing is still done by hand; the blower dips a long tube into the molten glass, then blows through the tube as if inflating a balloon.
The tremendous output of books and newspapers today means that many thousands of tons of paper have to be made every year. What was once a laborious process carried out by hand is now a highly mechanised industry. Paper is made of esparto grass, rag, wood-pulp or various mixtures of these materials. These are reduced to a fibrous pulp, boiled, and bleached. The pulp then travels along a moving belt over a suction chamber which removes excess moisture. The sheet which is formed through this process goes between rollers and drying cylinders until it emerges as a roll of white paper.