1765 – Glasgow, Lanarkshire, UK
Watt’s steam engine was the driving force behind the industrial revolution and his development of the rotary engine in 1781 brought mechanisation to several industries such as weaving, spinning and transportation.
Although THOMAS NEWCOMEN had developed the steam engine before Watt was even born, Newcomen’s machines had been confined to the world of mining.
In 1764, when Watt was asked to repair a scale model of Newcomen’s engine he noted its huge inefficiency. The heating and cooling of the cylinder with every stroke wasted huge amounts of fuel; and wasted time in bringing the cylinder back up to steam producing temperature, which limited the frequency of strokes. He realised that the key to improved efficiency lay in condensing the steam in a separate container – thereby allowing the cylinder and piston to remain always hot. Watt continued to improve his steam engine and developed a way to make it work with a circular, rotary motion. Another of his improvements was the production of steam under pressure, thus increasing the temperature gap between source and sink and raising the efficiency in a manner later described by SADI CARNOT and elucidated by JAMES JOULE.
RICHARD ARKWRIGHT was the first to realise the engine could be used to spin cotton, and later in weaving. Flour and paper mills were other early adopters, and in 1788 steam power was used to paddle marine transportation. In the same year, Watt developed the ‘centrifugal governor’ to regulate the speed of the engine and to keep it constant.
Watt was the first to coin the term ‘horsepower’, which he used when comparing how many horses it would require to provide the same pull as one of his machines. In 1882 the British Association named the ‘watt’ unit of power in his honour.
1757 – Edinburgh
‘Different quantities of heat are required to bring equal weights of different materials to the same temperature’
This definition relates to the concept of specific heat.
Through meticulous experimentation and measurement of results he discovered the concept of ‘latent heat’, the ability of matter to absorb heat without necessarily changing in temperature.
True in the transformation of ice into water at 0degrees C, the same principle applies in the process of transforming water to steam and indeed, all solids to liquids and all liquids to gases.
Through this work Black made the important distinction between heat and temperature.
JAMES WATT benefited from these discoveries during his development of the condensing steam engine.
Black’s insistence on the importance of quantitative experiments was a step towards setting the standard for modern chemistry.
Although JAN BAPTISTA VAN HELMONT had identified the existence of separate, distinct gases in air over a century before, Black is still often credited with the discovery of carbon dioxide (fixed air) – despite that van Helmont had clearly been aware of its existence.
He outlined the cycle of chemical changes from limestone (calcium carbonate) to quicklime (calcium oxide) and fixed air (carbon dioxide) when heated; quicklime mixed with water to become slaked lime (calcium hydroxide); which when combined with fixed air becomes limestone again (turning the solution cloudy).
Observing the effect that removing carbon dioxide from the limestone made the latter more alkaline, he deduced that carbon dioxide is an acidic gas.
Black was able to prove that carbon dioxide is made by respiration, through fermentation and in the burning of charcoal, but that the gas would not allow a candle to burn in it nor sustain animal life.
Black’s student Daniel Rutherford (1749 – 1819) called this gas ‘mephitic air’ after the mephitis of legend, a noxious emanation said to cause pestilence, for animals died in an atmosphere of the new gas. Rutherford’s ‘air’ is not the same as LAVOISIER’s mephitic air, which is nitrogen (azote).