Considered by many to be the founding father of Chemistry, Joseph Black has contributed greatly to our understanding of the effects of heat and temperature on substances. He discovered carbon dioxide during one of his experiments and made significant contributions to our understanding of how heat and temperature vary.
Joseph Black was born in Bourdeaux on 16th April 1728. His father was a wine merchant from Ireland and his mother Scottish. When he was 12 years old he was sent to school in Belfast, before going to university in Glasgow to study medicine and later studied at Edinburgh University where he obtained his MD.
Between 1750-52, Black worked on the chemistry of ‘magnesium alba’- a basic magnesium carbonate. It was during this time that he discovered a substance he called ‘fixed air’ – what we now know to be carbon dioxide. This was a breakthrough as it was commonly believed that air consisted of only one gas. He measured changes to the magnesium alba when heated and caused the products to react with acid or alkaline substances. In this instance, Black disproved ‘Phlogiston theory’ which had been widely accepted until this point. Phlogiston theory claims that there is a substance called ‘inflammable earth’ which is present in every flammable substance. During combustion, this substance would cause phlogiston to be released into air’ Black’s work in this area was a significant breakthrough. He observed the changes in masses related to the release of carbon dioxide from heated substances. He proved that carbon dioxide was a product of respiration as well, he did this by bubbling pure carbon dioxide through an aqueous solution of Calcium Hydroxide, which would precipitate Calcium Carbonate, which he then used to prove Carbon Dioxide was a product of respiration and also fermentation.
Black also researched the nature of heat and how it relates to temperature. During this time there were several ideas theorising on what heat was and how it affected the chemistry of substances. One theory suggested that liquids contained an inner fire which would be released when the liquid solidified. Another suggested heat was a tangible chemical substance which moved between hot and cold substances. Many of these ideas were in conflict with one another and little was actually understood at this time. Black’s meticulous experiments allowed him to clarify the distinction between heat and temperature clearing up some of the gaps in scientific knowledge of the time.
One of Black’s colleagues observed that certain substances produce extreme cold when they evaporate. This brought Black’s attention to the fact that snow was very slow to melt even when the air surrounding it increased in temperature. He realised the snow must be gradually taking in the heat from the environment without increasing in temperature. This, he called latent heat. And this latent heat, Black discovered, is the characteristic amount of energy absorbed or released by a substance without being preceded by a change in its temperature. His discovery here contributed greatly to Thermodynamics and extinguished the popular thoughts of the time.
Black also worked on Heat Capacity, a value that indicates the quantity of heat a specific material can hold. He was set onto this idea by something he had read in Boerhaave’s text, in which is detailed an experiment by Fahrenheit in which, when mixing equal quantities of mercury and water, Mercury had far less an effect in either heating or cooling compared to the water, in essence, the warm water heated the mercury far more than the warm mercury heated the water, and vice versa. This lead Black to stating that the mercury must have a smaller store of heat, despite having the greater density.
Despite his success in the field of pioneering chemistry, Black preferred his work as a lecturer, inspiring a great number of young students into the field of chemistry. He was also know to have been a friend and mentor to the inventor James Watt, and is credited for helping in his revolutionary invention of the separate combustion chamber in a steam engine.
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