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been advanced, and in concert with my colleagues, to take measures for adopting every necessary correction that had been suggested: but, in justice to the original members of the Committee, I cannot hesitate to declare, that, even granting the truth of all the chemical facts adduced by their opponents, the Work exhibited nothing like those gross errors which a too captious severity of criticism had repeatedly attributed to it, and that almost every one of the charges, relating to the chemical department, have been absurdly and ridiculously exaggerated.
But whatever these errors may have been, I am at a loss to understand to which of them your remark can at present be supposed to apply, when two re-impressions of the work have appeared, in which, with the assistance derived from the experiments of a practical chemist obligingly recommended by yourself, all possible care has been taken to make every correction that candour could allow to be requisite. I therefore feel myself personally bound to call on you for such an explanation of your censure, as will enable me to answer your objections in detail; and I will venture to pledge myself to prove, that the College of Physicians has not recorded its deficiency in any of those points which are "imperiously required" for the due performance of all the practical duties of the profession. I am, dear Sir, your faithful and obedient Servant, Welbeck Street, June 11, 1818.
My dear Sir,
To Dr. Thomas Young.
The remark in my dissertation, refers exclusively to the London Pharmacopoeia for 1809; the errors of which I cannot by any means consider as cancelled by the subsequent re-impressions, as you most charitably call them. I am sorry, therefore, that I cannot honourably recant; and regret that the Committee did not contrive to avail itself of your services previous to the publication, instead of merely appointing you an additional member," when the mischief was done.
This is perhaps sufficient explanation of my censure. Should more substantial grounds be required, I refer to Mr. Richard Phillips's experimental examination of the Pharmacopoeia for VOL. V.
1809 in the facts there disclosed, you cannot fail to discern
The evident carelessness of the College, as a body, was uppermost in my mind when I wrote the offending paragraph; and the very circumstance of the list of FELLOWS being adorned with the names of men highly eminent in chemical science, renders that carelessness more unaccountable, and may well be urged in justification of my remark. I hope, therefore, that on the whole, my inclination was rather to eztenuate, than set down aught in malice; to adduce nothing that was false, rather, than all that was true; and experience one only source of regret, that of having occasioned any unfriendly feeling in one for whom I have such unfeigned respect and regard as yourself.
I am, dear Sir, your faithful and obedient Servant, Albemarle Street, June 12, 1818. W. T. BRANDE.
2. Reduction of Chloride of Silver by Hydrogen. The following method of reducing chloride of silver, is perhaps not sufficiently known. It was communicated by M. Arfwedson. Liberate hydrogen in contact with chloride of silver, as by mixing the chloride, zinc, sulphuric acid, and water together, and the silver will be reduced to the metallic state; the zinc is easily dissolved out by excess of acid, and the metal obtained by filtration or decantation.
3. Prize Question of the Academy of Sciences at Paris for 1819. The Royal Academy of Sciences at Paris give as the subject for the prize essay to be decided March, 1819—“To determine the chemical changes which take place in fruits during and after their ripening.
"For the solution of this question, the influence of the atmosphere which surrounds the fruit, and the change it suffers, ought to be examined with attention.
"The observations may be confined to a few fruits of different kinds, provided that general consequences can be drawn from them."
The reward is a gold medal 3000 francs in value, and the latest period at which any memoir can be received will be 1st. January 1819.
The subject of a second reward is as follows:
"1st. To determine by direct and accurate experiments, all the effects of the diffraction of rays of light, either direct or reflected, when they pass separately or together near the extremity of one or many bodies of an extent either limited or indefinite, having regard to the intervals of those bodies as well as to the distance of the luminous focus from whence the rays emanate.
"2d. To conclude from those experiments by mathematical induction the motion of rays in their passage near to bodies."
The reward is a gold medal of the value of 3000 francs.
As the meetings close on the 1st of August 1818, the memoirs should be remitted to the secretary of the Institute before that time, that the experiments made, may be verified. Gottingen Chemical Prize for 1819.
The Royal Society of Gottingen has offered a prize of fifty ducats for "An accurate examination founded on precise experiments of Dalton's theory of the expansion of liquids and elastic fluids, especially of mercury and atmospheric air by heat."
The authors are to pay attention to the necessity alleged by Dalton for changing the progression of the degrees of the present thermometrical scales. The memoirs must be trans-. mitted to the Society before the end of September, 1819.*
5. Boiling point of Fluids.
M. Gay Lussac has in a late Number of the Annales de Chimie, shewn that the boiling point of water and other liquids varies independently of atmospheric pressure. The circumstances which influence it appearing to be the nature of the body which is in contact with the boiling fluid, the cohesion of the fluid, and the resistance which is opposed to a change of state, as in the cases of every other equilibrium of forces.
Water boiled in a glass vessel rises to a temperature of more
* This question has been discussed in a Paper lately read to the Royal Society, by Dr. Ure.
than one degree of the centegrade thermometer higher than when boiled in a metallic vessel; and the effect appears to be due to the nature of the surface in contact with the fluid; this is rendered evident by placing a metallic surface in contact with water boiled in a glass vessel. If a flask of water he placed over a lamp until its temperature be raised to the point of ebullition, and it be noticed, and then a portion of iron filings thrown in, the temperature will fall, and the boiling will go on, as in a metallic vessel.
It is to be observed that this effect of difference of temperature appears to be not so much a constant and specific effect as the apparent result of other circumstances. Water boiled in a glass vessel and open to the air, is continually changing its temperature, sometimes rising and sometimes falling within a certain minute range, and these changes accord with the evolution of vapour from the fluid. Either water or alcohol, when boiled in glass vessels, do not generally give off vapour in a regular uniform way, but whole torrents rise at once from the under surface with great force, producing a kind of explosion; the fluid is then quiet for a moment, and then another gust of vapour rises up. Now, during the time the vapour rises the temperature falls, and whilst the fluid is quiet the heat rises, so that it is continually changing; and as the lowest point is the true boiling point, it is evident that the mean temperature of water boiled in a glass vessel must be above that point. In a metallic vessel, on the contrary, as soon as the water or fluid has attained the boiling point, the conversion into vapour commences, and if the heat is continued, the steam is constantly and regularly generated and given off.
M. Gay Lussac seems inclined to account for the effect in glass vessels by the cohesion of the fluid to the surface of the vessel. It is evident that when vapour is formed in the interior of a liquid body, one force to be overcome is the cohesion of the particles of the liquid; this force will of course be constant for the same liquid in vessels of every material. An analogous force is that exerted between the liquid and the substance of the vessel, and this will vary with the substance; and as the vapour is generated at the point of contact be
tween the fluid and the vessel, the variation of this force will vary the temperature at which vapour will be formed.
M. Gay Lussac also gives, as another power which has influence in these phenomena, the resistance to a change of state; but observes, that it is difficult to analyze and describe; and he concludes in this part, that the conducting power for heat, and the nature of the surface, appear to exert an influence on the boiling point of water; and that every thing else being equal, water boils more readily on a metallic surface than on a glass surface, and more readily in a glass vessel containing glass in powder, than in a glass vessel containing nothing but the fluid.
The application which M. Gay Lussac proposes to make of the property which metals have of inducing ebullition before glass or earthen ware vessels, is to prevent those sort of explosions which take place in distillations. If into a retort, or flask, containing alcohol, water, or particularly sulphuric acid, some little pieces of platinum wire be put, the concussions, which are so violent as sometimes to break the vessels, will be prevented, and the vapour formed and liberated in a regular manner. This mode has been adopted for some years in this country by the makers of vitriol, where glass vessels are used to distil in. Where the retort is made of platinum, it is obviously unnecessary.
M. Gay Lussac observes, that an important consideration in the graduation of thermometers arises from the above facts, and that the variation pointed out ought to be guarded against, as a source of error.
6. Oxide of Lead crystallized.
Mr. Houtan Labillardiere has described a crystallization of the oxide of lead from its solution in soda. The solution had been left to itself during the winter, and had deposited many small crystals of a regular dodecahedral form, white, and semitransparent. They were insoluble in water; on burning charcoal, were reduced to lead; and were not diminished in weight when heated in a platinum crucible. They dissolved without effervescence in nitric acid, the solution was not rendered