faction. The belemnite, we may add, is one of the rarest fossilsi n Scotland. Professor Jameson observed it in lime-stone connected with sand-stone and basalt in the Island of Mull; and Mr. Neill found it in slate-clay covered with columnar green-stone in the Shiant Islands; but no other localities have hitherto been mentioned.

It appears to be the opinion of Werner that different rock formations can be discriminated by the petrifactions which they contain. How far this opinion may hold true with respect to the petrifactions of Germany, we have not the means of ascertaining; but in this country it cannot be considered as the expression of a general law in the distribution of organic remains. In the transition lime-stone which occurs between the Crook and Noblehouse there are a few impressions of bivalve shells, so closely resembling in appearance the shells found in the floetz lime-stones as to lead to the conclusion that they belong to the same species. In the lime-stone connected with the old red sand-stone in the Island of Arran there is a particular species of the genus productus of Sowerby, which is one of the most common petrifactions in the lime-stones of the Independent Coal Formation of the Lothians and Fife. If we descend from classes and formations to the individual members of a group, it will be found that the remains of the same species of vegetable are distributed through beds of clay-iron-stone, sand-stone, limestone, slate-clay, and slate-coal, as I have frequently observed.

The occurrence of the genus of shells which we have been considering in beds of lime-stone, is regarded by some as a proof of such lime-stones belonging to the transition class of rocks. Thus Von Buch, in his Travels through Norway, appears to have ferred the lime-stones of that country to the transition class, merely from the circumstance of their containing the remains of orthoceratites. In describing the mineralogical appearances which presented themselves in the neighbourhood of Christiana, where he had discovered rocks of the transition class, he says, "How great was my joy when, at the steep falls of Aggers Elv, above the lower saw-mills, I discovered the orthoceratites, which so particularly distinguish throughout all Europe this formation (transition limestone), and this formation alone. They are many feet in length, divided into compartments, and for the most part at the edge and the walls of the compartment changed into calcareous spar. They are by no means unfrequent; several of them generally lie in various directions through one another. Pectinites, and several other not very distinguishable petrifactions, appear frequently between them." English Trans. p. 47.-In the transition limestones of this country no orthoceratites have been found. They occur in beds of slate-clay and lime-stone of a more recent period. Thus it appears that the distinguishing character of a rock formation

See Professor Jameson's Mineralogy of Dumfriesshire, p. 77.

in Norway and Germany is not applicable to the same formation in Britain.

The same species of organic remains which occur imbedded in different strata of the floetz class, appear to have sustained the shock of several revolutions before the total destruction of their tribe; and we may also suppose that part of the race of orthoceratites survived the period of the deposition of the transition class, but became at last enveloped in the beds of the coal formation.

I cannot conclude these observations without taking notice of the great difference in point of size between the existing species of the genus orthocera and those orthoceratites which are found in the mineral regions. The living species of the genus to be met with on the British shores do not exceed a quarter of an inch in length, and required the aid of the microscope for their examination. Only one species has been found in Scotland, the O. linearis. (Testacea, Brit. Tab. 30, fig. 9.) It was found by Mr. Montagu in a parcel of minute shells sent to him from Dunbar. It is only a quarter of an inch in length; and its breadth is about one-eighth of its length.

Manse of Flisk, Fifeshire.

ARTICLE VII.

On Deepening, Cleaning, Excavating, and Removing Obstructions that prevent Vessels from entering Harbours. By John Rook, jun. of Akehead, Wigton, Cumberland.

WHEN We examine the force and power of water, we are convinced that it is an engine capable of performing various powerful operations. In its course from the uplands, and through the lowlands, till immersed in the Ocean, it forms for itself spacious channels and deep pools. When man brings its gravitating motion under subjection he obtains a useful and faithful servant, that performs for him numerous important labours. Passing from these reflections to a new modification of the use of that element, there seems to be a probability that it might be rendered useful in the improvement of the entrance of harbours, &c. by means of carrying it through tunnels, formed according to the circumstances of situations. These tunnels or pipes might be constructed either by collected materials, such as stone, wood, and metal, or formed by sinking down to the rock, and directing the tunnel in it according to the object in view. The use to which I would apply the principle is that of passing through these tunnels or pipes as powerful a stream of water as could be obtained; by which means considerable quantities of sand, gravel, &c. might be removed by the violent stream of water issuing forth from its confined channel.

Thus Plate XXXI. fig. 11,

a, a, the river flowing into the sea.

b, b, b, sand or gravel, being the object of removal. c, c, c, the rock.

d, d, d, the tunnel formed in the rock by mining.

e, e, e, large augur holes, according to circumstances.

In this way I expect several new harbours might be formed, old ones deepened, cleaned, &c.; and eventually, in all likelihood, many of those dangerous bars, such as Dublin and Linmouth, removed.

Letting the tide flow into a part of a harbour, and then shutting it in by gates, might frequently be resorted to as a means of obtaining a stream of water.

Akehead, Wigton, Cumberland,

Dec. 20, 1814.

I remain yours truly,

JOHN ROOK, Jun.

P. S. I should wish to hear the opinion of any engineer upon the above.

ARTICLE VIII.

A Memoir on Iodine. By M. Gay-Lussac.

(Continued from p. 109.)

AZOTE does not combine directly with iodine. We obtain the combination only by means of ammonia. It was discovered by M. Courtois. I shall give it the name of ioduret of azote. It has been accurately analyzed by M. Colin, and I shall briefly state from him the circumstances of its formation and its nature.

When ammoniacal gas is passed over iodine, a viscid shining, liquid is immediately formed, of a brownish black colour, which, in proportion as it is saturated with ammonia, loses its lustre and viscosity. No gas is disengaged during the formation of this liquid, which may be called ioduret of ammonia. It is not fulminating. When dissolved in water, a part of the ammonia is decomposed; its hydrogen forms hydriodic acid; and its azote combines with a portion of the iodine, and forms the fulminating powder. We obtain the ioduret of azote directly by putting iodine in fine powder into a solution of ammonia in water. This indeed is the best way of preparing it; for the water is not decomposed, and seems to concur in the production of this ioduret only by determining the formation of hydriodate of ammonia.

The ioduret of azote is pulverulent, and of a brownish black colour. It detonates from the smallest shock, and from heat with a feeble violet colour. I have often seen it detonate spontaneously when properly prepared. When put into potash, azote is dis

engaged, and the same products are obtained as when iodine is dissolved in that alkali. The hydriodate of ammonia, which has the property of dissolving a great deal of iodine, gradually decomposes the fulminating powder, while azote is set at liberty. Water itself has this property, though in a much weaker degree, as M. Courtois observed long ago. Thus the elements of ioduret of azote are but very little condensed. It ought to be prepared with great precautions, and should not be preserved.

It would be difficult to determine by direct experiment the proportion of the principles of this compound; but we ascertain them correctly in the following manner :

We have seen that the ratio of hydrogen to iodine is 1.3268 to 156.21; and as ammonia is composed of

Hydrogen
Azote

....

...

18.4756
81.5244

it follows that the ratio of azote to iodine is that of 5.8544 to 156-21; and such is the ratio of the clements of the fulminating compound. If we reduce these elements to volumes by dividing 5.8544 by 0.96913, the density of azote, and 156.21 by 8.6195, the density of the vapour of iodine, we find that the proportion in volume of the elements is one azote and three iodine. We obtain this proportion directly by observing that the vapour of iodine and hydrogen combine in equal volumes; and that in ammonia the volume of hydrogen is to that of azote as three to one.

If we decompose a gramme (15.444 grains) of the fulminating powder, we obtain, at the temperature of 32°, and under the pressure of 30 inches of mercury, a gaseous mixture amounting to 0.1152 litre (7.03 cubic inches, and composed of 0.0864 of the vapour of iodine and 0.0288 of azote. Though this volume be inconsiderable, yet the explosion is very loud, because it is instantaneous. The same difficulty occurs here as in the detonation of the chloruret of azote, and of all the fulminating bodies which are decomposed into simple substances, producing at the same time heat and light. I do not pretend to resolve this difficulty; but is it not possible that the heat and light which make their appearance in these cases is produced by the shock of the gas produced against the air, or any other fluid, as happens when air is compressed or introduced into a vacuum? * Is it in fact necessary to have recourse to heat to communicate elasticity to gaseous substances condensed in a compound, or, which is the same thing, to put their elements in a state of repulsion? Do we not see, on the contrary, a weak electricity destroy the combinations which resist the repulsive force

To explain my idea the better, let us conceive a volume of air in the middle of which is a small metallic ball, containing any elastic fluid in a great degree of compression, and at the same temperature with the surrounding fluid. If we suppose the ball suddenly to burst, which will represent a detonation, we shall have heat and light produced. Now in the detonation of ioduret or chloruret of azote the developement of the gas does not appear to me to differ from that of air strongly compressed in our hall.

of a very high temperature? * Supposing these conjectures to have some foundation, it will remain to explain why, when we mix equal volumes of water and of a solution of nitrate of ammonia at the same temperature, the thermometer, as I have observed, sinks more than 9°, though there is a notable increase of density. On the supposition that the capacity of bodies for heat is a function of the absolute quantity of heat which they contain, this fact would lead us to admit that the capacity of the solution of nitrate of ammonia is greater than that of its constituents; but this consequence does not appear to be confirmed by experience; therefore the capacity of bodies for heat does not depend solely upon the absolute quantity of heat which they contain.

I return now to the combinations of iodine with the combustibles, or with those oxides which, not being saturated with oxygen, act like combustibles. I have already spoken of the action of iodine on hydro-sulphuric and phosphorous acids. It remains only to speak of its action on sulphurous acid. In the gaseous state this acid has no action on iodine; but when dissolved in water, the addition of iodine occasions a decomposition of that liquid, and sulphuric acid and hydriodic acid are produced. They cannot be separated by distillation; for at the temperature at which hydriodic acid comes over, sulphurous is reproduced. The liquid in the

Chemical phenomena, in my opinion, cannot be explained by heat alone, supposing them to depend solely on the variation of distance which it produces in the particles of these bodies. M. Laplace remarks (Systeme du Monde, 3d edit. ii. 256) that, in order to conciliate planetary attraction with chemical affinity, 66 we must suppose the dimensious of the particles so smail, when compared with the distances between them, that their density is incomparably greater than the mean density of the whole together. A spherical particle, whose radius is equal to the millionth of a metre, ought to have a density more than six thousand thousand millions greater than the mean density of the earth to produce at its surface an attraction equal to gravitation; but the attractive force of bodies considerably surpasses that of gravitation, as they inflect visibly the rays of light, whose direction is not sensibly changed by the attraction of the earth. Hence the density of atoms would prodigiously surpass that of bodies, if their affinities were only modifications of universal gravitation."

Such a supposition appears exaggerated; but let us admit it for a moment, and see whether the diminution of the affinity of a body corresponds with the increase of the distance of its particles produced by heat. Without knowing exactly the cohesion of copper, for example, in a solid and liquid state, we may admit that it is at least a thousand times greater in the former than in the latter state. Let us suppose also, to keep greatly below the truth, that copper in melting increases eight times in bulk. On this exaggerated supposition the distance between the particles of the copper would have only become double; so that the cohesion should have been only four times smaller if it followed the same law as gravitation. Hence it is obvious that, when heat accuinulates in a body, it does not diminish the affinity merely by increasing the distance of the particles, but by increasing in a great degree the power of their repulsive faculty, which is doubtless the same with their electric faculty. The figure, the arrangement, and the inertia, of the atoms, may have influence in some chemical phenomena; as, for example, in the congelation of water, and the crystallization of sulphate of soda. But there are an infinity of others which are independeut of these, as well as of the separation of the atoms. Such is the combination of hydrogen with oxygen, which takes place only at a red heat, whether the gases be În a condensed or rarified state.

VOL. V. No III.