Joseph Priestley House

Northumberland, Pennsylvania

Priestley and Science

Compiled by Derek A. Davenport
Department of Chemistry
Purdue University

“Hitherto philosophy has been chiefly conversant about the more sensible properties of bodies; electricity, together with chymistry, and the doctrine of light and colours, seems to be giving us an inlet into their internal structure, on which their sensible properties depend. By pursuing this new light therefore, the bounds of natural science may possibly be extended, beyond what we can now form an idea of.”

“When I began these experiments, I knew very little of chemistry…But I have often said that upon the whole this circumstance was no disadvantage to me; as in this situation I was led to devise an apparatus of my own, adapted to my peculiar views. Whereas, if I had been previously accustomed to the usual chemical processes, I should not have so easily thought of any other; and without new modes of operation I should hardly have discovered anything materially new.”
-JRC, p. 71

“I own I had that expectation, when I first put a sprig of mint into a glass jar, standing inverted in a vessel of water; but when it had continued growing there for some months, I found that the air would neither extinguish a candle nor inconvenience a mouse.”
“I have had some appearances, which extraordinary as it will seem, make it rather probable, that light is necessary for the formation of this substance (algae).”
“I have discovered what I long have been in quest of, viz, that process in nature by which air, made noxious by breathing, is restored to its former salubrious condition.”
-Letter to Theophilus Lindsay (1771)

“All the time that I was making these experiments, I wrote to my friends about them, particularly to Mr. Magellan, and desired him to communicate my observations to you, as well as to others; but I believe you had not heard of them; so that what you did with leaves was altogether independent of what I was doing with whole plants. The same summer, and the same sun, operated for us both, and you certainly published before me.”
-Letter to Jan Ingenhousz

“As I never made the least secret of anything that I observe, I mentioned this experiment also, as well as those with mercurius calcinatus, and the red precipitate, to all my philosophical acquaintances at Paris, and elsewhere; having no idea at that time, to what these remarkable facts would lead.”

“The feeling of it [dephlogisticated air or oxygen] to my lungs was not sensibly different from that of common air; but I fancied that my breast felt peculiarly light and easy for some time afterwards. Who can tell but that, in time, this pure air may be a fashionable article of luxury. Hitherto only two mice and myself have had the privilege of breathing it.”

“From the greater strength and vivacity of the flame of a candle, in this pure air, it may be conjectured, that it might be particularly salutary to the lungs in certain morbid cases, when the common air would not be sufficient to carry off the phlogistic putrid effluvium fast enough. But, perhaps, we may also infer from these experiments, that though pure dephlogisticated air might be useful as a medicine, it might not be so proper for us in the usually healthy state of the body; for as a candle burns out much faster in dephlogisiticated than in common air, so we might, as may be said, live out too fast, and the animal powers be too soon exhausted in this pure kind of air. A moralist, at least, may say, that the air which nature has provided for us is as good as we deserve.”
-Experiments and Observations on Different Kinds of Air (1776)

“The more we see of the wonderful structure of the world, and of the laws of nature, the more clearly do we comprehend their admirable uses, to make all the percipient creation happy: a sentiment, which cannot but fill the heart with unbounded love, gratitude and joy.”
-The History and Present State of Electricity (1776)

“The greater is the circle of light, the greater is the boundary of the darkness by which it is confined. But, notwithstanding this, the more light we get, the more thankful we ought to be. For by this means we have the greater range for satisfactory contemplation.”
-Experiments and Observations on Different Kinds of Air (1790)

“There have been few, if any, revolutions in science so great, so sudden, and so general, as the prevalence of what is now usually termed the new system of chemistry, or that of the Antiphlogistians, over the doctrine of Stahl, which was at one time thought to have been the greatest discovery that had ever been made in science…Though there had been some doubts of the existence of such a principle as that of phlogiston, nothing had been advanced that could have laid the foundation of another system before the labours of Mr. Lavoisier and his friends, from whom this new system is often called that of the French.”
-Considerations on the Doctrine of Phlogiston and the Decomposition of Water (1796)

“But I consider no hypothesis as of any use but to assist us in discovering new facts, which new facts serve in turn to correct the hypothesis; till, at length, by this method of approximating we shall have discovered all the facts, and have got a perfect theory.”
“Speculation is the cheapest of commodities.”
“In forming any general theory we must content ourselves with the fewest difficulties.”
“Though the title of this work expresses perfect confidence in the principles for which I contend, I still shall be ready to adopt those of my opponents, if it appears to me that they are able to support them. Nay the more satisfied I am with the doctrine of phlogiston, the more honorable I shall think it to give up on conviction of its fallacy.”
-Doctrine of Phlogiston Established (1801)

“A philosopher who has long been attached to a favorite hypothesis, and especially if he has distinguished himself by his ingenuity in discovering or pursuing it, will not sometimes be convinced of its falsity by the plainest evidence of fact.”

“…phlogiston, if there be such a thing as phlogiston.”