has been discovered in Holland, yet no pains are taken to procure a knowledge of it in this country, though that disease has occasioned the loss of many millions of property to the subjects of Great Britain within these fifty years past. If that loss had not been sustained, would not the wealth of the country have been considerably augmented, its public revenue consequently increased, and of course great quantities of human food have been preserved from destruction, which have perished, to the manifest injury of the nation!

Remarks on the Resistance of Fluids. By Dr. Young.

From the JOURNALS of the ROYAL INSTITUTION Of
GREAT BRITAIN.

MR. Lacroix has inserted in the Bulletin de la Société

Philomathique, a comparative view of the experiments of Mr. Bossut and of Mr. Vince, on the resistance of fluids striking on oblique surfaces. He does not appear to have assigned a sufficient reason for the difference of the results of those experiments; but the subject is of so much importance, as to deserve such an examination in its present state as may serve to assist in the prosecution of farther experiments.

The first approximation to a determination of the effect of the resistance to a body of a given section, terminated by oblique planes, is to suppose each particle of the fluid to impinge once on the surface, and then to retire for ever on this supposition, the resistance ought to vary as the square of the cosine of the angle of incidence.

Another part of the resistance is occasioned by the adhesion of the particles of the fluid; this may be supposed VOL. IV.-SECOND SERIES.

R.

to

to vary, as the product of the secant and the sine of the angle of incidence; that is, as its tangent.

A third part depends on the form of the posterior surface of the body, and upon the unknown irregularities produced in the motions of the particles of the fluid, by the difference of the forms of its anterior part. It may be expected, that this negative pressure will be nearly uniform, when the shape of the posterior part of the body remains unaltered, as in Bossut's experiments; but that, when a thin surface is employed, as in Mr. Vince's apparatus, it will be somewhat diminised by the obliquity of that surface, even supposing the transverse projection of the surface to remain unaltered. This portion, however, may naturally be expected to be liable to great irregularities; and it appears to be somewhat increased when the thin surface is inclined in a small angle only.

In order to inquire how far these suppositions agree with the experiments, we may examine the curves of which the ordinates express the resistances. And if we make the abscisses equal to the squares of the cosines, the figure corresponding to the first part of the resistance will be a triangle. To this we may add a figure, of which the ordinates are in proportion to the tangents, and by comparing the results with the curves deduced from experiment, we may find what remains to be explained by the third supposition of a negative pressure, and other accidental irregularities.

Thus the ordinates of the curves R, B, and R, V, (see Fig. 5, Plate VI.) may represent the resistances determined by Bossut and Vince respectively: those of the line T, S, the first portion, proportionate to the square of the cosine; the distance between this line and T E, the second portion, proportionate to the tangent; and the distance between T V, and the former curves, the

third portion, which, in Bossut's experiments, appears to decrease slowly, and almost regularly, while the obliquity increases, as might be expected from the analogy of other experiments. In those of Mr. Vince, on the contrary, this regularity is lost.

We may obtain a simple approximation to the results of Bossut, by neglecting the third portion, and adding to the square of the cosine one-tenth of the tangent: this approximation is represented by the curve RY, which is tolerably accurate, as far as 70° of inclination. Mr. Eytelwein's formula (Journals, vol. I. p. 149,) gives the curve R E. The simple ratio of the cosines, represented by the curve RS, approaches nearer to the results of Mr. Vince's experiments than any of the other determi

nations.

I have before observed, that the resistance opposed by a fluid, to the motion of a surface moving obliquely through it, might be divided into three portions; arising respectively from impulse, from tenacity, and from negative pressure; and that in such experiments as those of Bossut, where the posterior part of the substance remains unaltered, the negative pressure might be supposed to be nearly constant, the resistance from tenacity to vary as the tangent of the angle of incidence, and the effect of impulse nearly as the square of its cosine.

Mr. Romme has remarked, that the facility with which the particles of the fluid can escape before the moving body, is proportional to the angular space of the fluid which remains open to admit them, and that therefore the resistance must vary in proportion to this angle. Without allowing the truth of the observation in its whole extent, we may with propriety inquire, whether or no the portion of the pressure derived from impulse may not in part depend on some simple function of the angle of incidence;

R 2

Method of obtaining perfectly pure Metallic Cobalt,

MIX

By M. TROMMSDORFF.

From the JOURNAL DE CHIMIE,

one pound of the best safflower with four ounces of nitrate of potash and two ounces of pulverized charcoal, and throw this mixture, in small portions, into a red-hot crucible. Repeat the operation three times'; after the third time leave the matter exposed for an hour to a white heat; agitate it quickly, and add four ounces of black flux; then remove the crucible into the furnace, and keep it red-hot for an hour. When cold, separate the reduced part of the cobalt, which, by the treatment it has undergone, has by this time lost a great portion of its arsenic and iron, but is not yet quite pure, since it may still be easily pulverized notwithstanding its natural density is considerable. It is then mixed afresh with three times its weight of nitrate of potash; the mixture is thrown, in small portions, into an ignited crucible, which is kept red-hot for a certain time. By this last operation the iron is completely oxydated, the arsenic is converted into acid, and combined with the potash. levigation with warm water it is cleared from all saline particles, and the oxyd of cobalt is separated by the filtre. The oxyd is dissolved in a proper quantity of nitric acid; the solution is filtered, and evaporated to dryness. Then add fresh acid, expose it to a moderate heat, dilute with a sufficient quantity of water, filtre, in order to separate the last portions of iron, precipitate with pure potash, and reduce it.

By

Extract

Extract from a Memoir on the febrifuge Principle of

Quinquina. By M. SEGUIN.

From the BULLETIN DES SCIENCES.

THE aim of the author in this paper was to indicate the means of discovering, with certainty, the real febrifage principle of quinquina, of distinguishing those species which contain it from those which do not, and to ascertain the quantity and quality.

Hitherto a judgment has been formed of the quality of quinquina, only by the taste and by inspection; but as those methods established no fixed data, and could not be employed with quinquina in powder, the presence of the febrifuge principle was very imperfectly ascertained by them. It was therefore an object of considerable importance to substitute for those almost illusory methods, others not only reducible to calculation, but likewise invariable. Chemical re-agents alone were capable of cffecting this purpose.

M. Seguin, in consequence, began with separating the respective properties of all medicinal substances, and examined their action upon all other chemical substances. These researches led him to the discovery, that the febrifuge principle of quinquina possesses very striking characters, which place it in a class distinct by itself.

These characters are; it precipitates the solution of tan, but does not precipitate solutions of gelatine and sulphate of iron. When quinquina does not possess all these characters, it is a proof that it has been adulterated, or that it does not contain the febrifuge principle.

To