The Science Book

76

A

professor of medicine at

the University of Glasgow

and later at Edinburgh,

Joseph Black also gave lectures

on chemistry. Although he was a

notable research scientist, he rarely

published his results formally, but

instead announced them during his

lectures; his students were at the

cutting edge of new science.

Some of Black’s students were

the sons of Scottish whisky

distillers, who were concerned

about the costs of running their

businesses. Why, they asked

him, was it so expensive to

distill whisky, when all they were

doing was boiling the liquid

and condensing the vapor.

An idea brought to the boil

In 1761, Black investigated the

effects of heat on liquids, and

discovered that if a pan of water is

heated on a stove, the temperature

increases steadily until it reaches

IN CONTEXT

BRANCH

Chemistry and physics

BEFORE

1661 Robert Boyle pioneers

the isolation of gases.

1750s Joseph Black weighs

materials before and after

chemical reactions—the first

quantitative chemistry—and

discovers carbon dioxide.

AFTER

1766 Henry Cavendish

isolates hydrogen.

1774 Joseph Priestley isolates

oxygen and other gases.

1798 American-born British

physicist Benjamin Thompson

suggests that heat is produced

by the movement of particles.

1845 James Joule studies the

conversion of motion into heat

and measures the mechanical

equivalent of heat, stating

that a given quantity of

mechanical work generates

the same amount of heat.

Heat generally raises the temperature of water.

But when water boils, the temperature stops rising.

The heat that disappears in the conversion

of water into vapor is not lost.

Additional heat is needed to turn the liquid into vapor.

This latent heat gives steam a terrible scalding power.

THE HEAT THAT DISAPPEARS

IN THE CONVERSION OF

WATER INTO VAPOR

IS NOT LOST

JOSEPH BLACK (1728–1799)