and resistance to the water's motion, arises from its action against the containing sides, it follows, that a greater velocity, upon the same inclination, will be generated in the latter section than the former; that is, it will run more water through the same section, or the same quantity of water being determined, since a lesser inclination will suffice to generate the same velocity, the canal will empty itself at the upper end to a lower level, and thereby better drain the land.

"To resume my former illustration, of a canal 10 miles long, and 10 feet deep of water, being supplied at one end, with as much water as will form a cascade at the other end, running a quarter of an inch deep; the width is not material, if we suppose the cascade to be of equal width with the canal ; though, for the sake of fixing our ideas, we will suppose the width 60 feet, I say, that (without applying to calculation) I should not expect the rise of the canal at the entering end, in order to discharge such a quantity, to be above 2 inches higher than the cascade end, whereas, was you to conduct the same quantity of water for 10 miles, upon a bottom inclined from the solid top of the cascade, so as to run nowhere deeper than a quarter of an inch, I do not suppose an inclination of 100 feet would bring it, though you was to bring it on boards planed and jointed as smooth as art could make them.

"I therefore consider a canal having 4 feet natural descent in 16 miles, dug upon a dead level bottom, as equivalent to a canal dug, in the whole, 2 feet deeper than if the bottom is made to rise 4 feet in that length; and with less expense of leakage; because a canal dug with a sloping bottom, in the whole 2 feet deeper, must for one-half of it be dug under level of the natural discharge; and the level bottom will have this further advantage in dry times, when the quantity entering becomes very little, that the surface of the canal at the upper end will fall nearly to the level of the lower, whereas in the inclined bottom it can never run below the bottom; this circumstance may sometimes indeed be a disadvantage, by reducing the water in the drains, in the interior part of the drainage, too low; but where descent is scarce, and consequently the drainage is liable to be languidly, or imperfectly performed, it will be a very great help, in getting the drainage of the same more early completed; and after all there are always means of restraining it."

Letter from Mr. Grundy to Mr. Smeaton, July 31st, 1770.

"I cannot but be satisfied with the reasoning contained in your solution of that

question, as being metaphysically true; yet I cannot say I am convinced, that the highest advantages obtainable in point of velocity, by digging a drain to a dead level, can by any means compensate for the additional expense which must attend such practice, especially where the fall is anything considerable; and was that to become a fixed principle, it might be construed to extend and operate in some cases, so as to introduce 10 or 20 feet unnecessary depth to be dug; and as it but rarely happens that the falls we find in countries to be drained are by nature made sufficient to convey their waters to sea, by proper drains made on a parallel to the inclination of the plane of the surface, I yet think it more eligible to pursue that practice; and more particularly so, because in the other instances, where the fall is found inadequate for a natural drainage, engines must be introduced to perform it artificially. I do not recollect that we proposed making our drains on a dead level in our schemes for the drainage of the country connected with the Foss Dyke."*

Mr. GILES contended, in spite of what had been stated, that a depth of two feet below low-water mark at sea was sufficient for drainage, as all marshes were situated at a level between high and low-water marks.

Sir JOHN RENNIE said he could not have any hesitation in admitting the correctness of the principle of level bottoms, for main drains, in very flat districts; but almost every case of drainage had peculiar features, and in the Ancholme, it must be remembered, that in a distance of about 14 miles there was a fall of nearly 20 feet; while in the catch-water drains, into which the high-land waters descended with a certain velocity, there was a far greater fall; therefore the rising bottom was not only not injurious but was highly advantageous in that instance; because it enabled the floods to be carried away with sufficient rapidity, without incurring the extra expense of cutting the drain so much deeper. The case of the middle level was totally different there, as Mr. Walker very properly stated, the fall being only about 18 inches in 30 miles, there was no alternative but to make the bottom of the drain level, and to give great sectional area, because those drains must act as reservoirs to receive the great mass of water which inevitably fell into them, and which could only be discharged during the short time the sea sluices were open at each tide; but even presuming that the cill of the outfall sluice be laid from 6 feet to 8 feet below low-water mark in the Ouse; still when the

Vide Smeaton's Reports, vol. i. p. 82 (4to. 1762.)

river Ouse should be improved below Lynn, as was contemplated, the low-water mark in front of the sluice, proposed by Mr. Walker, would be lowered 5 feet or 6 feet, so that the cill of the sluice would then be only about 2 feet below low-water mark, as Mr. Giles had stated.

Sir GEORGE CAYLEY observed, that he had been for more than thirty years one of the directors, for carrying out the provisions of the Muston Drainage Act, including about 10,000 acres of land near Scarborough. This drainage was effected under the direction of the late Mr. William Chapman, of Newcastle-upon-Tyne, who had great experience in such matters. The drains appeared to combine in their just and most economical proportions, the two adverse principles at issue in the previously expressed opinions. In that extensive and gently rising marsh, the dead level principle was adopted from the lowest outfall, till the surface of the water in the drain, at ordinary times, was within about 4 feet of that of the soil, which level was found sufficient for the purpose of draining the adjacent lands. From this point, the drains took the average rise of the marsh, and continued it for several miles; thus furnishing, at the cheapest possible rate, a very useful and efficient drainage, to all the lands under the Act. Had the dead level been continued throughout the whole length, the expense would have been enormous, without rendering the drainage more complete, and had the dead level not been brought up to the point named, many hundred acres of the lower portion of the swamp would not have received any benefit.

The general plan of the Muston Drainage might be thus stated. The small rivers Hartford and Derwent, with several brooks, held their courses through an extensive marsh, and in times of heavy rain they overflowed their banks and flooded the land to a great extent. No expense whatever was incurred for cutting channels, deep enough to convey away the flood waters of these rivers, or brooks, but they were allowed to keep their ancient levels, and embankments were made near them, on each side, by cutting deep back drains, for carrying the dead water from the lands, and casting up the soil excavated from them, on to the sides next the rivers or brooks. By this process, all the great body of water was conveyed, in times of flood, within these embankments to the lowest outfall; and the deep cutting, which he considered the sine qua non of an efficient drainage, and the expensive part of it, was entirely confined to such moderate-sized drains as were sufficient

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merely to convey the dead water from the land. Another practical advantage, of the deep back drains being contiguous to the embankments, was, that when they received any injury from cracking, after long droughts, or the burrowing of moles and water rats, and thus permitted the flood-water to pass in some degree through them, the back drains interrupted it, and preserved the land from injury.

The original cost of this drainage was about 40,0007.; and the annual repairs averaged about 8001. The improved rent was obtained at about four or five years' purchase.

The expense of this drainage had been much increased by local circumstances, and which could scarcely be supposed to occur in any other cases, and therefore it was unnecessary to detail them; but these circumstances took place at a distance from the marsh land, and in no way invalidated the state of the case.

Sir JOHN RENNIE said, that Mr. Telford, in his drainage works, had as nearly as possible acted upon an uniform system, similar to that which had been described; but that, in particular cases, it was necessary to adopt peculiar methods. It was certain, however, that in all cases it was essential to commence the drainage at the lowest point of outfall, and to work inwards, towards the head of the marsh. In the Bedford Level that system had been neglected, and to that circumstance Sir John Rennie attributed much of the difficulty that had been experienced.

It was always a point of importance to restore the rivers to their natural state, of main drains for the country. At Boston, in the year 1826, he recollected seeing the bed of the river nearly dry, at the time of wha ought to have been high water. Since thent the outfall below Boston had been improved, by making a cut across Burton's Marsh' and improving the channel of the river upwards, upon a plan proposed by him; the effect of these works had been such, that vessels, drawing upwards of 14 feet of water, now arrived at Boston.

THE MIXTURES MOST SUITABLE FOR OBTAINING BY ELECTRIC PRECIPITATION COPPERPLATES OF SUPERIOR FINENESS. BY PROFESSOR VON KOBELL.

[From Translation in Silliman's Journal.] "In order to attain a uniformity in the current, I tried what would be the effect of adding to the solution of the sulphate of copper other salts, which resist the action of such feeble currents as are here called into

play, and I thus obtained a copper of the most admirable quality. The salts I thus employed were Glauber's salt, sulphate of zink, potash, alum, and saltpetre. Chlorides are not available; for they become decomposed and thus act on the silver on which the pictures are painted. These salts, or rather the saturated aqueous solutions, with the exception of the sulphate of zink, take up as much sulphate of copper as common water does. I have determined the amount of the oxide of copper contained in an ascertained quantity of these solutions, and have ascertained therefore, by calculation, what is the quantity of sulphate of copper which they take up. I find that 100 parts by weight of spring water dissolve about 27 parts of sulphate of copper; 100 parts of a solution of Glauber's salt 27.5; 100 parts of a solution of potash alum, 27·4; 100 parts of nitrate of potash, 25'4; but 100 parts of sulphate of zink, only 7 parts of sulphate of copper.

"As a precipitation fluid, there are two mixtures which I usually employ,—the first consisting of two parts, by measure, of a saturated aqueous solution of sulphate of copper, mixed with one part, by measure, of a similar solution of the sulphate in a solution of Glauber's salt; the second consists of the same quantity of the solution of sulphate of copper, with the addition of one part, by measure, of a solution of the sulphate in a solution of sulphate of zink. There are, however, other proportions; for instance, equal parts, by measure, of the various solutions which afford satisfactory results; indeed, a simple solution of sulphate of copper in a solution of Glauber's salt, will afford an extremely malleable copper, which, when as much as half a line thick, is perfectly flexible, and presents a very even surface."

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"Occasionally, however, the two copper plates, thus prepared, adhere together so firmly that there is no possibility of separating them; but this difficulty is altogether obviated by the following process, which was first communicated by me to the Academy of Sciences, at their meeting of the 11th December, 1841.

"If we form a concentrated solution of common salt, and dissolve chloride of silver in it, (this is done by adding thereto a suitable quantity of a solution of nitrate of silver, shaking the precipitate well up in the fluid, and then letting it settle,) and into this liquor dip a clean strip of copper, it will be observed that, in from ten to fifteen minutes, there forms upon the surface thereof an infinitely thin film of firmly ad

hering metallic silver, so thin that on washing the plate and drying it with a towel, and rubbing it with a piece of wash leather, it presents the appearance of copper again.

"A similar coating of platina may be obtained by adding to a similar solution of salt (till the liquor assumes a pale wineyellow colour) a few drops of a solution of platina, as neutral as possible. About oneeighth of an ounce of the solution of platina is required for a pound of the solution of salt. It takes about two hours for the film of platina to form completely upon the copper plate; but it adheres as well as the silver, if not better. In order to clean properly the plates thus coated, they are to be laid for five or six minutes in dilute muriatic acid, and then washed in warm water. If, when thus washed, they assume a bluish or yellowish hue, they must be again dipped in the diluted muriatic acid, and washed in cold water. The deposition of this film of silver or platina is very materially influenced by the quality and the nature of the copper surface; but it is precisely upon this galvanic copper, owing to its purity, that these films are thrown down in the most perfect state; and, as they form most readily upon smooth surfaces, they prevent the plates from growing together at the very spot where their tendency to adhere is the greatest. Anything approaching a modification in the copy is out of the question by this process; for, strictly speaking, these films are not coats upon the copper, but rather they replace a portion of that metal from the surface of the plate, inasmuch as there is an interchange between the atoms of platina or silver in solution, and those of the copper.

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"From the power of the currents depends the facility with which the plates may be separated, when the silver or platina is used, or whether, when neither of those substances are employed, the plates can be parted at all, or not."

circumference of the screw blades. There can be no doubt, I think, that the dead-water will be less at B, than at A, and consequently, if the blades are pitched to suit the velocity of the vessel passing through the water at A, it will be just so much wrong at B, and vice versa, and therefore, no advantage will be gained by following his recommendation of "increasing the pitch of the blades from the centre to the circumference."

I am, Sir, your old subscriber,
Esher, Surrey, October 30, 1845.

T. W.

Sir, In the last Number of your valuable Magazine, there is a description of a new (?) propeller, and in a postscript, the reader is referred to Appendix D, of Tredgold, for a

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sketch, showing the after current of a vessel. If your correspondent had read this Appendix through, he would have found at page 62, a very accurate and full description of this same propeller, which description also appeared in your, Magazine, vol. xxxvii., page 180. Now, if your correspondent, "P. P.," had not been what I subscribe myself, he would not have troubled you and the readers of the Mechanics' Magazine, with the article alluded to.

་་་

Yours,

Blackwall, October 27, 1845.

LIEBIG'S PATENT MANURES... We have had a great many enquiries respecting the nature of these manures, and we are glad to be at length enabled by the enrolment of the learned and distinguished inventor's specification, to gratify the prevailing curiosity on the subject. The patent for them was taken out, on Dr. Liebig's behalf (April 15, 1845) in the name of Mr. James Muspratt, of Liverpool. For ourselves, we must confess, (in all proper humility, of course,) that we are anything but overwhelmed with the value of the great Giessen Professor's revelations. We can discover nothing in his specification which was not well known before; and see much in it which is calculated rather to perplex, than enlighten the agricultural mind."

The Specification.

To all to whom these presents shall come, &c., &c.-It has been ascertained, that the growing of any crop on land in a state of cultivation, and the removing and consuming of such crop wholly from the land where it was grown, takes away certain mineral compounds; and it has been suggested by Professor Liebig, that in cultivating land and applying manure thereto, that the manure should be such as to restore to the land the matters and the quantities thereof, which the particular plants have abstracted from the soil during their growth. It has been observed in the chemical examination of marls and vegetable ashes, that the alkaline carbonates and the carbonate of lime can form compounds, the solubility of which depends on the quantity of carbonate of lime contained in the particular compound. It has further been found, that the said alkaline carbonates can form alike compound with phosphate of lime, in which the carbonate of potash or soda is partly changed into phosphate of potash or soda.

Now, the object of this invention is to prepare manure in such manner as to restore to the land the mineral elements taken away by the crop which has been grown on and removed from the land, and in such manner, that the character of the alkaline matters used may be changed, and the same rendered less soluble, so that the otherwise soluble alkaline parts of the manure may not be washed away from the other ingredients by the rain falling on the land, and thus separating the same therefrom. And it is the combining carbonate of soda or carbonate of potash, or both with carbonate of lime, and also the combining carbonate of potash and soda with phosphate of lime, in such manner as to diminish the solubility of the alkaline salts to be used as ingredients for manure (suitable for restoring to the land the mineral matters taken away by crop which which may have been grown on and removed from the land to be manured,) which constitutes the novelty of the invention.

I would here state, that although the manures made in carrying out this invention will have various matters combined with the alkaline carbonates, no claim of invention is made thereto separately, and such materials will be varied according to the matters which the land to be manured requires to have returned to it, in addition to the mineral substances above mentioned. The quantity of carbonate or phosphate of lime, used with carbonate of soda or potash, may be varied according to the degree of solubility desired to be obtained, depending on the locality where the manure is to be used, in order to render the preparation less soluble, in localities where the average quantity of rain falling in the year is great; but as in practice, it would be difficult to prepare manures to suit each particular locality with exactness, I shall give such average preparation as will suit most localities. And as lands differ very greatly, it would be impossible to give directions in this specification for making manure according to this invention, which would produce the best results on all soils, I shall therefore only give such average preparations as will suit most soils as manure, and I will afterwards give such information as will enable parties desirous of applying the invention under the most advantageous circumstances to have manure manufactured for their particular cases. In making manure according to the invention, I cause carbonate of soda or of potash, or both, to be fused in a reverberatory furnace, such as is used in the manufacture of soda-ash, with carbonate or phosphate of lime, (and with such fused compounds I mix other ingredients as hereafter mentioned,) so as to pro

duce manures; and such composition, when cold, being ground into powder by edge stones or other convenient machinery, the same is to be applied to land as manure. And in order to apply such manure with precision, the analysis and weight of the previous crop ought to be known with exactness, so as to return to the land the mineral elements in the weight and proportion in which they have been removed by the crop.

Two compounds are first prepared, one or other of which is the basis of all manures, which I shall describe as the first and second preparations.

The first preparation is formed by fusing together two or two and a half parts of carbonate of lime with one part of potash of commerce (containing on an average sixty carbonate of potash, ten sulphate of potash, and ten chloride of potassium or common salt in the hundred parts,) or with one part of carbonate of soda and potash, mixed in equal parts.

The second preparation is formed by fusing together one part of phosphate of lime, one part potash of commerce, and one part of soda ash.

Both preparations are ground to powder; other salts or ingredients in the state of powder are added to these preparations and mixed together, or those not of a volatile consistency may be added when the preparations are in a state of fusion, so that the manure may represent as nearly as possible the composition of the ashes of the preceding crop. This is assuming that the land is in a high state of cultivation; but if it be desired to grow a particular crop on land not in a high state of cultivation, then the manure would be applied in the first instance suitable for the coming crop, and then in subsequent cases, the manure prepared according to the invention would, as herein described, be applied to restore to the land what has been taken therefrom by the preceding crop.

Preparation of Manure for Land which has had a Wheat crop grown on and removed therefrom.

Take of the first preparation six parts by weight, and of the second preparation one part, and mix with them two parts of gypsum-one part of calcined bones-silicate of potash, (containing six parts of silica)— and one part of phosphate of magnesia and ammonia.

And such manure is also applicable to be used after growing barley, oats, and plants of a similar character.

Preparation of Manure for Land which has