Daniel Gabriel Fahrenheit (1686-1736)

Experimenta circa gradum caloris liquorum nonnullorum ebullientium instituta

Phil. Trans. 33, 1 (1724) [from William Francis Magie, A Source Book in Physics (New York: McGraw-Hill, 1935)]

About ten years ago I read in the History of the Sciences issued by the Royal Academy of Paris, that the celebrated Amontons, using a thermometer of his own invention, had discovered that water boils at a fixed degree of heat. I was at once inflamed with a great desire to make for myself a thermometer of the same sort, so that I might with my own eyes perceive this beautiful phenomenon of nature, and be convinced of the truth of the experiment.

I therefore attempted to construct a thermometer, but because of my lack of experience in its construction, my efforts were in vain, though they were often repeated; and since other matters prevented my going on with the development of the thermometer, I postponed any further repetition of my attempts to some more fitting time. Though my powers and my time failed me, yet my zeal did not slacken, and I was always desirous of seeing the outcome of the experiment. It then came into my mind what that most careful observer of natural phenomena had written about the correction of the barometer; for he had observed that the height of the column of mercury in the barometer was a little (though sensibly enough) altered by the varying temperature of the mercury. From this I gathered that a thermometer might perhaps be constructed with mercury, which would not be so hard to construct, and by the use of which it might be possible to carry out the experiment which I so greatly desired to try.

When a thermometer of that sort was made (perhaps imperfect in many ways) the result answered to my prayer; and with great pleasure of mind I observed the truth of the thing.

Three years then passed, in which I was occupied with optical and other work, when I became anxious to try by experiment whether other liquids boiled at fixed degrees of heat.

The results of my experiments are contained in the following table, of which the first column contains the liquids used, the second their specific gravity, the third, the degree of heat which each liquid attains when boiling.

Gravity of Degree
Liquids at Attained
Liquids 48 of heat by Boiling.
Spirits of Wine or Alcohol 8260 176
Rain Water 10000 212
Spirits of Niter 12935 242
Lye prepared from wine lees <15634 240
Oil of Vitriol 18775 546

I thought it best to give the specific gravity of each liquid, so that, if the experiments of others already tried, or which may be tried, give different results, if might be determined whether the difference should be looked for as resulting from differences in the specific gravities or from other causes. The experiments were not made at the same time, and hence the liquids were affected by different degrees of temperature or heat, but since their gravity is altered in a different way and unequally, I reduced it by calculation to the degree 48, which in my thermometers holds the middle place between the limit of the most intense cold obtained artificially in a mixture of water, of ice and of sal-ammoniac or even of sea-salt, and the limit of heat which is found in the blood of a healthy man.

Volatile oils certainly begin to boil at a fixed degree, but their heat is always increased by boiling. Perhaps this is because the more volatile particles readily leave while resinous particles possessed of greater attraction remain.

On the other hand fixed oils are affected by so much heat that the Mercury of the thermometer begins to boil at the same time as they do and hence their heat can hardly be explored by the aforementioned method. But I devised another method which I hope to have the honor of describing in another session before the illustrious Royal Society.

Except water and the spirit of wine, perhaps the degree of other liquors here documented will also vary, particularly if they are present in a large enough quantity and if they boil for a longer time.