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tem. He then calculates the velocity of the blood in the least arteries, and estimates the effect of its viscidity in increasing the friction against the sides of the vessels.
In commencing his second subject of inquiry, Dr. Young observes that the propagation of the pulse is extremely analogous to the motion of waves on the surface of water, or of sound transmitted through air; and that the same calculations are of course applicable to the three cases. The experiments of Hales are again quoted as the data on which the conclusions are founded respecting the velocity of the pulse ; and from this velocity is deduced the degree of the dilatation of the vessels, the former quantity being estimated at 16 feet in a second, and the increase of capacity in the aorta at one-sixteenth of its bulk. Then, assuming that, in the small arteries, the force of the pulse must diminish in the subduplicate ratio of the increase of the sum of their areas, we are told that, in the vessels of the 20th order, the dilatation does not exceed the 160th part of their diameter, which will be no more than the 140th of an inch. On this circumstance the author justly observes, that it is not surprizing that Haller should have been unable to discover any dilatation in vessels of these dimensions, even with the assiste ance of a powerful microscope.'
Having thus endeavoured to ascertain the extent of the dilatation which the arteries experience during the course of the circulation, we proceed in the 3d place to consider the nature of the functions which are to be attributed their muscular coats. Their dilatation being shewn to be considerably less than it has been generally imagined, Dr. Y. infers that their effect, in propelling the blood along the vessels, is likewise much less than it had been supposed : an opinion grounded not only on the small degree of contraction which these muscular fibres seem to exert, but likewise on the velocity with which the pulse proceeds along the vessels ; since it is obvious that, in order to produce any effect, the contraction must advance along the vessel as rapidly as the pulsation. Dr. Young, however, prcperly remarks that in some cases the circulation must necessarily have been effected merely by the power of the vessels ; as in the substances called moles, which have been produced in the uterus without a heart, and in a numerous class of the imperfect animals, which are destitute of this organ. With respect to the first case, he conjectures that the blocd may have been carried on in an uniform current, like the sap of vegetables ; or that there may have been some peculiarity in the structure of the placenta. The former supposition we can scarcely admit as affording any kind of explanation, since it is merely exchanging one difficulty for another not less obscure. We should incline
to conjecture that, in these instances, some of the large vessels act as substitutes for the heart, and are accordingly furnished with powers which are accommodated to the individual occasion. In the imperfect animals, it is allowed that the aorta is only a heart of a different form. Even the volume now before us contains the account of a fcetus, which had arrived at a considerable state of perfection without a heart, and in which the circulation must have been performed by some accessory power of this description. The real use of the muscular coats of the arteries does not appear to consist in the propulsion of the blood; and Dr. Young imagines that they are chiefly serviceable in accommodating the capacity of the blood-vessels to their contents, which from many causes are frequently varying. With regard to the states of the pulse which are perceptible by the touch, the author observes that they must depend almost entirely on the action of the heart; although the tension of the arteries may cause it to feel a little harder or softer, and the yielding of the longitudinal fibres may render the vessel rather tortuous. When an artery appears to throb, it must be in a state of increased dilatation, and must receive a greater portion of the force of the heart, similarly to the case of an aneurism ; and when the pulse is unusually feeble, as in a paralytic limb, the vessels must be in a state of permanent contraction : but it does not appear that the effect, in either of these instances, depends on the action or energy of the artery itself.
Dr. Young devotes the remainder of his paper to the consideration of the causes, general or partial, which produce derangement of the circulation ; either as constituting, in the one case, the states of fever, or, in the other, local inflammation. Admitting that the muscular fibres have little influence in producing these conditions, they must be referred to some change in the action of the heart, or in the capacity of the capillaries. Our boundaries will not permit us to follow the author through all his deductions : but we may say of them, as of the paper in general, that they exhibit considerable learning and ingenuity, and certainly deserve the attention of the physiologist. We are not, indeed, prepared to assent to all Dr. Young's positions, and we think that he has relied too implicitly on the experiments of Hales, which, though highly valuable, are not to be received without many allowances. In some cases, we are not sure that we fully comprehend the meaning of the writer ; since a degree of obscurity prevails in his style, by which an investigation, that is in itself sufficiently abstruse, is rendered still more difficult.
An Account of some Experiments, performed avith a view to ascertain the most advantageous Method of constructing a Voltaic
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Apparatus, for the Purposes of Chemical Research. By J. G. Children, Esq. F.R.S.- This paper consists of some experiments made on a Galvanic apparatus of different forms, which serve to illustrate the observation that the same surface of metal produces different effects, according as it is divided into small or large plates. In constructing the apparatus, the author recommends that the disks of copper and zinc should be joined together at one part only, rather than soldered through their whole surface, and that, instead of being cemented into a wooden trough, they should hang loose into cells formed of earthen
The Bakerian Lecture. An Account of some new Analytical Researches on the Nature of certain Bodies, particularly the Alkalies, Phosphorus, Sulphur, Carbonaceous Matter, and the Acids hitherto undecompounded; with some general Observations on Chemical Theory. By Humphrey Davy, Esq., Sec. R.S. F.R.S. Ed., and M.R.I.A. --The Bakerian lecture of this year consists of an account of a great number of most interesting experiments performed by Mr. Davy, in which he has applied his new method of analysis to several substances that had hitherto been regarded as simple bodies. The whole paper occupies above 60 pages; so that it will be in our power to present our readers merely with an abstract of some of the most curious and important of the results.—Professor D. begins by a farther investigation of the effects which he had before noticed from the mixture of potassium and ammoniac. He had stated that, when these bodies are exposed together to a powerful heat, hydrogen gas is disengaged while the potassium becomes oxydated; from which he concluded that ammoniac, like the other alkalies, is an oxyd of some unknown base. The correctness of this opinion having been called in question, Mr. Davy deemed it necessary to repeat the process with every possible precaution; and especially with a reference to some experiments of MM. Gay-Lussac and Thenard, the results of which did not entirely correspond with those which he had formerly obtained. The conclusions that are deducible from the latter experiments of Professor Davy serve to prove the accuracy of the former; and he is moreover successful in pointing out the source of the error into which the French chemists have fallen. It appears that, when potassium and ammoniac are heated together, hydrogen is disengaged, and the potassium is oxydated, and united to a peculiar substance which seems to be the metallic basis of the ammoniac. Although this fact may be considered as clearly established, yet several theoretical difficulties attend it. The substance which is procured from the above process ought to consist of potassium united to oxygen and nitrogen : but, on submitting it to a va
riety of operations, for the purpose of removing the nitrogen, it never could be procured in a quantity at all corresponding to the hydrogen which had been evolved. The author proposes a number of ingenious queries on this point, and promises to make it the subject of his future researches,
Sulphur was the next object of experiment. Mr. Davy submitted it, in a state of fusion, to his powerful Galvanic apparatus, and he obtained a gas which was found to be sul phuretted hydrogen : the quantity of gas which the sulphur was capable of affording seemed to be indefinite, while the sulphur itself was converted into a substance of a deep redish brown colour. The same gas was extricated by the action of sulphur on potassium. On the whole, it seemed to be proved that sulphur contains hydrogen; and many circumstances render it probable that oxygen also enters into its composition. The general conclusion respecting it is that sulphur, in its common state, is a compound of small quantities of oxygen and hydrogen with a large quantity of a basis that produces the acids of sulphur in combustion, and which, on account of its strong attractions for other bodies, it will probably be very difficult to obtain in its pure form. Experiments of a similar kind were instituted on phosphorus, and the results were usually analogous ; so that in this case it is rendered highly probable that phosphorus is a compound of some unknown base with hydrogen and oxygen, though the quantity of these latter substances may be comparatively small.
We next proceed to the examination of the different car. bonaceous bodies, plumbago, charcoal, and diamond. These, the author observes, have been found to produce the same quantity of carbonic acid, and to absorb the same quantity of oxygen during combustion ; so that they must consist principally of the same kind of elementary matter. He was still, howeyer, inclined to believe that the great variation, which exists in their physical properties, does not depend merely on the difference of the mechanical arrangement of their particles, but likewise on differences in their intimate chemical nature. This opinion was found to be correct, for he observed considerable variations in the results of his experiments, when he subjected these several bodies, under similar circumstances, to the action of the Galvanic apparatus. Plumbago appeared pot to be affected by the most powerful battery, nor was any gas evolved when it was heated in contact with potassium. Charcoal, however, under the same circumstances, extricated a quantity of inflammable gas, and was, by the operation, converted into a substance bearing the external
characters of plumbago. The experiments did not afford any ground for suspecting the presence of oxygen in charcoal. Diamond, on the other hand, by being heated in contact with potassium, gave indications of the existence of a small quantity of oxygen ; so that, at present, we are led to suppose that plumbago contains the pure carbonaceous matter in union with iron only, that charcoal contains a little hydrogen, and diamond a little oxygen. Mr. Davy remarks that whoever considers the difference between iron and steel, in which there does not exist more than of plumbago, or the difference between the amalgam of ammonium, and mercury, in which the quantity of new matter is not more than
or that between the metals and their sub-oxides, some of which contain less than- of oxygen, will not be disposed to question the principle, that minute differences in chemical composition may produce great differences in external and physical characters.'
The three undecomposed acids, the boracic, the fluoric, and the muriatic, were each in succession subjected to Prof. Davy's potent apparatus, with the view of accomplishing their analysis. Of the first of these substances, the decomposition seems to have been completed ; and when the acid was submitted to the Galvanic influence, a dark coloured matter attached itself to the negative wire, which was inflammable, and by its union with oxygen became again converted into the boracic acid. It seemed to hold the same relation to its acid which sulphur and phosphorus bear to the sulphuric and phosphoric acids ; and we have reason to suppose that it is of a metallic nature. The decomposition of the fluoric acid ap: pears also to have been partially effected, but the results were less decisive than in the former case.
Mr. Davy's curious paper concludes with an account of the attempts which he has made to effect the decomposition of the muriatic acid : but this, notwithstanding his genius and perseverance, he has not yet been able to accomplish. He gives us a very interesting detail of the experiments which he performed with a vicw to this object, and we acquire from them some important information respecting the constitution of the acid. The great obstacle to its decomposition seems to be the powerful affinity which it exerts for water, so as to retain of its weight of this substance, after it has arrived at what is usually considered as a state of perfect dryness, Many curious operations were instituted for the purpose of