Henry Cavendish
1731 - 1810

Royal Connections. Henry Cavendish was born on October 10, 1731 in Nice, France, where his family was living at the time.  His mother was Lady Anne Gray, daughter of the Duke of Kent and his father was Lord Charles Cavendish, son of the second Duke of Devonshire.  The family traces its lineage across eight centuries to Norman times and was closely connected to many aristocratic families of Great Britain. 

Education.    At age 11, Henry Cavendish was a pupil at Dr. Newcome's School in Hackney.  At age 18, (1749) he entered Cambridge in St. Peter's College.  He left without graduating four years later.  His first paper Factitious Airs appeared 13 years later.

Eccentric in life.  Henry Cavendish had a peculiarly odd demeanor.  He was morbidly shy of women and strangers and avoided ever speaking to them.  He wore a coat of faded velvet and a three-cornered cocked hat from the previous century so he must have looked almost as curious to his con-temporaries as he does to us.  He admitted to a "singular love of solitariness."  He was a tall man with a thin, squeaky voice.  He spoke with hesitation and difficulty, especially when embarrassed.  At home, his servant was instructed by written notes what to prepare for dinner usually 'a leg of mutton.'

"[Cavendish] probably uttered fewer words in the course of his life than any man who lived to fourscore years."   -Lord Brougham"1

     Henry Cavendish was extremely wealthy, but was not bothered by money.  Through inheritances, he became the single largest holder of bank stock in England.  His single social outlet was his membership in the Royal Society Club, an organization whose members dined together before weekly meetings.  Cavendish seldom missed these meetings.  He was profoundly respected by his contemporaries.  Henry Cavendish died on March 10, 1810.2
 
 
Factitious Airs.  In this 1766 paper,3 Cavendish reported his results of careful quantitative study of gases already known using meticulous laboratory techniques.  He was also tedious, often repeating an experiment numerous times.  He dried the gases and compensated for temperature and pressure and characterized them for the first time by specific gravity. 

Hydrogen (Inflammable air). Cavendish is generally credited with the discovery of inflammable air which he eventually came to believe was pure phlogiston. Inflammable air had been collected and studied by others, starting with Boyle, for over a century, however Cavendish's careful studies involving specific gravity established the gas as a individual substance.  Prior to this, there were various inflammable airs including the gas produced from heating charcoal (now known to be CO).  Regarding the gas obtained from metals by dissolution in sulphuric or muriatic acid, Cavendish wrote:

"...their phlogiston flies off, without having its nature changed in the acid, and forms the inflammable air"


Equipment used by Cavendish for the manipulation of gases.

Water.  Cavendish will always be associated with a role in unraveling the composition of water through careful experimentation.

"...on applying the lighted paper to the mouth of the bottle... With 3 parts of inflammable air to 7 of common air, there was a very loud noise."4

"By the experiments with the globe it appeared that when inflammable and common air are exploded in a proper proportion, almost all of the inflammable air and near one-fifth of the common air lose their elasticity, and are condensed into dew."5

Sparks.  Explosions are initiated by spark.  In the 1760s the only known way to obtain an electric spark was to rotate a glass globe called an or cylinder while pressing a pad against it. 

     Cavendish went on to react dephlogisticated air (now O2) with inflammable air (H2) and established the optimal proportion as 2.02:1.

 deplogisticated air +  inflammable air gives water

[now: 2 H2(g) + O2(g)  H2O(l)]

Lasting accomplishments.

  Pioneer in the manipulation of gases, including collection in bottles by water displacement and methods for transferring gases.

  Cavendish established an accurate composition of the atmosphere (from hundreds of analyses) to be 79.167 % phlogisticated air (now N2 + Ar) and 20.833 % dephlogisticated air (now known to be 20.95% O2).  He went on to question "...whether there are not in reality many different substances confounded together by us under the name of phlogisticated air."5 and established that 1/120 is a third gas (Lord Rayleigh established the gas to be argon 100 years later)

  Cavendish's most famous accomplishment in science took place during the years 1796 - 8 during which he established the mean density of the earth to be 5.448.  The current estimate is 5.5.


References.

1 a quote of Lord Brougham, from A Short History of Chemistry, J. R. Partington, 3rd edition, (1957)

2 Much of what is known about the character of Cavendish was reported in various memoranda of his contemporaries including Sir Humphry Davy

3 Transactions of the Royal Society, 1766.  (The word, 'factitious' was from Robert Boyle.)

4 A Source Book in Chemistry 1400 - 1900, H. M. Leicester, H. S. Klickstein, Harvard University Press, 1968.

5 Famous Chemists, Sir William Tildon, London, 1921.


(This page last updated 25 September 2001)