Mr. Watt, which bears the much more. unequivocal title of "Thoughts on the Constituent Parts of Water, and of Dephlogisticated Air;' and of which the great object is to maintain that doctrine of the composition of water which is distinctly stated in its outset. M. Lavoisier, in his celebrated Memoir, admits that a partial communication was made by Blagden, to him and some other members of the French Academy, when, on the 24th of June, 1783, along with M. La Place, he tried the experiment which they reported to the Academy on the following day. "He informed us," says Lavoisier, "that Mr. Cavendish had already attempted to burn inflammable air in close vessels, and that he had obtained a very sensible quantity of water." He thus confines the extent of the communication within very narrow limits for neither the experiment nor the result, as thus reported, was anything more than had been effected by Warltire and Priestley. Evidently he did not intend to admit that he knew of any conclusion, as to the real origin of the water, having been drawn by Cavendish; for in a subsequent part of the same memoir, he takes to his coadjutor and himself the credit of drawing such conclusion:"we did not hesitate to conclude from it, that water is not a simple substance, and that it is composed, weight for weight, of inflammable air, and of vital air." He adds also, that they were then ignorant, and did not learn for some days, that M. Monge was occupied on the same subject. CHAPTER XXI. MR. WATT'S EXAMINATION OF DR. PRIESTLEY'S EXPERIMENTS IN MARCH and April, MR. WATT, in whose neighbourhood Dr. Priestley says he had "the happiness to be situated," and with whom, as has been. mentioned, he was on terms of friendship and frequent intercourse, had, previous to 1783, for many years entertained an opinion that air was a modification of water; and that, if steam could be made red-hot, so that all its latent heat should be converted into sensible heat, either the steam would be converted into permanent air, or some other change would take place in its constitution. "You may remember," he writes to Mr. Boulton,* "that I have often said, that if water could be heated red-hot or something more, it would probably be converted into some kiud of air, because steam would in that case have lost all its latent heat, and that it would have been turned solely into sensible heat, and probably a total change of the nature of the fluid would ensue." And, so early as 13th December, 1782, he talks of processes "by which," he says, "I now believe air is generated from water;" using the expression, "if this process contains no deception, here is an effectual account of many phenomena, and one element dismissed from the list.”† * 10th December, 1782. † Mr. Watt to Mr. De Luc, 13th December, 1782. ! LETTER TO DR. PRIESTLEY. 263 Being thus, even at that time, prepared to expect that water was, in some way or other, convertible into air, he directed his attention to Dr. Priestley's experiment, which he thus accurately relates: "He puts dry dephlogisticated air and dry inflammable air into a close vessel, and kindles them by electricity. No air remains, at least if the two were pure, but he finds on the sides of the vessel a quantity of water equal in weight to the air employed."* In less than a month after he thus mentions his knowledge of that experiment, we find him writing to Dr. Black that he believes he has found out the cause of the conversion of water into air;"† and giving the very words in which, both on that day, and a few days later, he stated his conclusions in the letter to Dr. Priestley, which he desired might be read to the Royal Society:-"In the deflagration of the inflammable and dephlogisticated airs, the airs unite with violence, become redhot, and, on cooling, totally disappear. The only fixed matter which remains, is water; and water, light, and heat, are all the products. Are we not then authorized to conclude, that water is composed of dephlogisticated and inflammable air, or phlogiston, deprived of part of their latent heat; and that dephlogisticated, or pure air, is composed of water deprived of its phlogiston, and united to heat and light; and if light be only a modification of heat, or a component part of phlogiston, then pure air consists of water deprived of its phlogiston and of latent heat?" The same conclusions are given in other letters written nearly at the same time; but nowhere are they more clearly, briefly, or forcibly stated, than in that to Mr. Gilbert Hamilton of the 22nd of April, where, after a short enumeration of FACTS, beginning with the result of Dr. Priestley's experiment, follow these DEDUCTIONS. "Pure imflammable air is phlogiston itself. "Dephlogisticated air is water deprived of its phlogiston, and united to latent heat. * To his brother-in-law, Mr. Gilbert Hamilton, 26th March, 1783. "Water is dephlogisticated air deprived of part of its latent heat, and united to a large dose of phlogiston." In writing to Mr. De Luc, four days afterwards, "These," says Mr. Watt, "seem bold propositions, but I think they follow from the present state of the experiments; and if I were at leisure to write a book on the subject, I think I could prove that no experiment hitherto made contradicts them, and that the greater number of experiments affirm them."* To others of his correspondents he announced his theory in similar terms. To Mr. Smeaton, writing that he has "attempted to demolish two of the most ancient elements-air and water;"† and to Mr. Fry, giving particular directions for the production of water and of [dephlogisticated] air:-" Dr. Priestley, as you observe, converts water into air, and air into water, and I have found out the reason of all these wonders, and also what air is made of, and what water is made of; for they are not simple elements.-I have written a paper on the subject, and sent it with Dr. Priestley's to the Royal Society. It is too long to give you even an abstract of it, but if you will forgive me the reasoning, I will add the receipt below for making both these elements. "To make Water.- "R. Of pure air and of phlogiston Q. S., or if you wish to be very exact, of pure air one part, of phlogiston, in a fluid form, two parts, by measure. Put them into a strong glass vessel, which admits of being shut quite close; mix them, fire them with the electric spark; they will explode, and throw out their elementary heat. Give that time to escape, and you will find the water, (equal in weight to the air,) adhering to the sides of the vessel. Keep it in a phial close corked for use. "To make Air.- "Take pure water Q. V., deprive it of its phlogiston by any ANNOUNCES HIS THEORY. 265 practicable method, add elementary heat Q. S. and distil. You will obtain pure air, to be preserved as above."* It will be remembered, that in the letter to Mr. Hamilton he had shown his belief to be, that pure inflammable air and phlogiston were exactly synonymous; and it is very remarkable, that the proportions of the two gases which he directs to be fired, viz., of pure air one part, and of inflammable air two parts, by measure, are exactly those which chemists of the present day would employ. It appears from the letter to Dr. Black of the 21st of April, that Mr. Watt had, on that day, written his letter to Dr. Priestley, to be read by him to the Royal Society; but on the 26th he informs Mr. De Luc, that having observed some inaccuracies of style in that letter, he had removed them, and would send the Doctor a corrected copy in a day or two, which he accordingly did on the 28th; the corrected letter, (the same that was afterwards embodied verbatim in the letter to Mr. De Luc, printed in the Philosophical Transactions,) being dated 26th April, and containing, almost at its very commencement, the following passages :— "The same ingenious philosopher mixed together certain proportions of pure dry dephlogisticated air and of pure dry inflammable air in a strong glass vessel, closely shut, and then set them on fire by means of the electric spark. The first effect was the appearance of red heat or inflammation in the airs, which was soon followed by the glass vessel becoming hot. The heat gradually pervaded the glass, and was dissipated in the circumambient air, and as the glass grew cool, a mist or visible vapour appeared in it, which was condensed on the glass in the form of moisture or dew. When the glass was cooled to the temperature of the atmosphere, if the vessel was opened, with its mouth immersed in water or mercury, so much of these liquids * 28th April, 1783. |