[57] I do not mean to deny the tribute of praise to Marriotte and Venel, any more than to Brownrigg and Lane, and it is certain that Lavoisier was engaged in pneumatic experiments, previous to 1774.
It is impossible to conclude the preceding account better than by the following extract of a letter to Mr. Lindsey from a man[58] well able to appreciate the labours of Dr. Priestley; and the late testimony in favour of his discernment by Dr. Bostock. “To enumerate Dr. Priestley’s discoveries, would in fact be to enter into a detail of most of those that have been made within the last 15 years. How many invisible fluids whose existence evaded the sagacity of foregoing ages has he made known to us? The very air we breathe, he has taught us to analyze, to examine, to improve: a substance so little known, that even the precise effect of respiration was an enigma until he explained it. He first made known to us the proper food of vegetables, and in what the difference between these and animal substances consisted. To him Pharmacy is indebted for the method of making artificial mineral waters, as well as for a shorter method of preparing other medicines; metallurgy for more powerful and cheap solvents; and chemistry for such a variety of discoveries as it would be tedious to recite: discoveries which have new modelled that science, and drawn to it and to this country, the attention of all Europe. It is certain that since the year 1773, the eye and regards of all the learned bodies in Europe have been directed to this country by his means. In every philosophical treatise, his name is to be found, and in almost every page. They all own that most of their discoveries are due either to the repetition of his discoveries, or to the hints scattered through his works.”[59]
[58] Richard Kirwan, Esqr.
[59] Vindiciæ Priestlianæ, p. 68.
“This is not the only instance” (says Dr. Bostock,[60] speaking of Mr. Jurin’s opinion that azote was generated, instead of being absorbed, in the process of respiration as Dr. Priestley, and after him Mr. Davy had supposed,) “in which, after the conclusions of Dr. Priestley have been controverted by his contemporaries, a more accurate investigation of the question, has ultimately decided in his favour. The complicated apparatus, and imposing air of minuteness which characterize the operations of the French chemists, irresistibly engage the assent of the reader, and scarcely permit him to examine the stability of the foundation upon which the structure is erected. The simplicity of the processes employed by Dr. Priestley, the apparent ease with which his experiments were performed, and the unaffected conversational stile in which they are related have, on the contrary been mistaken for the effects of haste and inaccuracy. Something must also be ascribed to the theoretical language which pervades, and obscures the chemical writings of this Philosopher, in consequence of his unfortunate attachment to the doctrine of Phlogiston.”
[60] Essay on respiration, p. 208.
When the operose experiment of the French chemists on the formation of water, shall have been sufficiently repeated, and verified by other experiments to the same point, less complex, less tedious, less expensive, and easy to be repeated; when the water thus supposed to be formed is sufficiently distinguished from the water absolutely necessary to the generation of all airs, and attendant upon them[61] both in a state of mixture and combination; and when the difficulties enumerated a page or two back, as attendant on the modern theory shall be explained on the new system, as well as on that of Stahl, then, and not until then, will it be time to lament Dr. Priestley’s unfortunate attachment to the doctrine of Phlogiston.
[61] Mr. Kirwan found that common inflammable air from iron, and vitriolic-acid, contained about 2-3 of its weight of water mixed with it; which might be separated from the air by means of concentrated vitriolic-acid in a watch glass over mercury, without diminishing the quantity or altering the characteristic properties of the air thus treated.
Of Dr. Priestley’s other Scientific Works.
The other philosophical labours of Dr. Priestley consist of his history of electricity, his history of the discoveries relating to light and colour, and his popular introductions to perspective, electricity and natural philosophy.