MECHANICAL CHIMNEY SWEEPING.

Sir,-Public attention has been very properly directed to a somewhat important matter in connexion with the forthcoming emancipation of the "little negroes of our own growth," by the notice which appeared at page 425 of your last volume.

The change which will then be complete, has already to a great extent taken place; machines are now become common, children scarce. Thanks to the indefatigable exertions of Mr. Stevens, and his humane coadjutors.

Lest the compulsory humanity which is now thrust upon us, should be productive of needless annoyance, I beg to add a few words for the guidance of housekeepers, on a point upon which they are open to deception.

There are at this time in use two kinds of machines for sweeping chimneys, known as Smart's and Glass's. The former consists of a number of short inelastic hollow rods fitting loosely one into the other, and connected by a rope passing through the whole. Never employ any person who uses this machine.

Glass's machine-which is sanctioned by parliament, and is the machine by which the perfect and efficient sweeping of chimneys by mechanical means was completely established-consists of a number of elastic bamboos firmly connected together by screwed ferule joints.* This machine is sufficiently pliable to sweep all ordinary chimneys, and with a little contrivance, every chimney in existence; while its firmness and stability enable the user to cleanse the chimney more effectually than boys have ever done.

Glass's, at present, is the only machine that can be depended upon; when chimneys require sweeping, therefore, see that this machine is employed: it differs so greatly from the other that there can be no mistake, and housekeepers may depend upon it, that those parties who will still continue to use the old inefficient machines, only do so for the purpose of causing annoyance and bringing mechanical chimney sweeping into disrepute, by showing how very badly chimneys can be swept by a bad machine, worked in the worst possible manner.

• Described with illustrated engravings, at page 184 of vol. ix.

BLASTING ROCKS UNDER WATER BY GALVANIC IGNITION.-IMPROVED APPARATUS INVENTED BY DR. HARE.

[From the Franklin Journal.]

In Vol. xii. of the last series of this Journal, (page 221,*) we published an article by Professor Hare, describing an apparatus for the blasting of rocks by means of galvanic ignition; and it will be seen, by the subjoined letter, that Captain Paris, a wellknown engineer and architect, of Boston, has applied the proposed means, with perfect success, in blasting rocks under water. In the article by Dr. Hare, Mr. Moses Shaw, of Nova Scotia, is mentioned as having first suggested the idea of igniting the powder in blasting rocks, by the aid of the electric fluid. That gentleman had pursued the subject with much persevering industry, contending, at the same time, against pecuniary difficulties, and a want of those resources which science alone can supply, in the prosecution of such undertakings. well merits, however, to have his name associated with those who have brought the matter to a successful issue.-EDITOR.

He

Dear Sir,-Knowing the great interest you have always manifested in all engineering operations connected with the construction of public works, it affords me pleasure to communicate to you an account of the transactions within the past summer at this Navyyard, in blasting rocks under water by means of the galvanic battery.

The application of this means to purposes of blasting is somewhat novel, as you are well aware, and the account of Colonel Pasley's experiments in England has given to the public the first notice of its being thus employed. Since the blowing up of the wreck of the Royal George, it has been successfully used in England in blasting rocks and clearing harbours, rivers, &c. from obstructions: it bids fair to entirely supersede the old methods of blasting, both in civil and military operations, especially in the latter, where it becomes a tremendous agent for the instantaneous explosion of mines, &c.

⚫ September, 1833.

69

In the detailed accounts of the experiments tried by Col. Pasley, it appears that at first many difficulties were encountered; and the numerous failures seemed to forbid any hope of success in large operations, although the result of those on a smaller scale generally proved satisfactory. Perseverance, however, enabled the operators, after many trials, to render the explosion of the charge under water as certain as by the ordinary methods on dry land; and the subsequent success in blowing up sunken wrecks, &c., at the bottom of the Medway river, and at Spithead, proved the utility of the means, and amply compensated for the labour and expense incurred in the first attempts.

Our operations during the past season were confined chiefly to the construction of quay walls and the foundations of two launching ways, the whole of which were built of stone. The character of the bottom of the river where the work was laid rendered blasting or other means necessary, before a proper surface for the foundation could be obtained; it was desirable to give it a slight inclination inwards, so that the face of each course of stone should lie somewhat higher than the inside, thus preserving a proper batter of the walls, and rendering them perfectly secure. This bottom is a hard slate rock, and, with the exception of some level portions, extremely uneven, with slopes of almost every grade, generally in an outward direction from the shore. The depth of water in the line of the walls varies from fifteen to twenty feet at low water, and from twenty-five to thirty below the high tides. This depth of water, added to a strong and variable current, caused me to anticipate much difficulty and great expense in all operations below its surface.

But we were, fortunately, provided with a fine diving apparatus, consisting of a castiron diving-bell, and a powerful air-pump attached. This apparatus was worked from a vessel of strong construction and light draught, fitted expressly for the purpose. A system of signals and messengers was established for communication between the workmen in the bell and those on board the vessel; by these means every want was speedily made known and answered. Four workmen, divided in two gangs, were employed for working in the bell, which made four descents per day, occupying at each time two and a half hours, the two gangs alternately relieving each other. The bell was amply supplied with a constant stream of fresh air, and but two or three inches of water remained in it at its greatest depth, so that the men worked in a comfortable state, perfectly dry, and with no more difficulty of respiration than on dry land.

In deciding upon the best means for pre

paring the bottom for the reception of the foundation of the walls, I was greatly at loss which to adopt. It appeared to me, that in adopting the method practised by Col. Pasley, great expense and difficulty would be incurred; and as it did not appear that this method had been employed in blasting the solid rock at the bottom of a river, in any of his experiments, I was somewhat apprehensive of its utility for operations of this kind, and whether the cost would justify the trial. In order to satisfy myself with regard to the expense of an experiment with the galvanic battery, I applied to Mr. Daniel Davies, junior, philosophical instrument maker, of Boston, for the necessary information, when I was convinced that a very trifling expense would procure such a trial as would satisfactorily decide the merits of the apparatus. Mr. Davis kindly assisted me in making the experiments which were tried at the Navy-yard at Charlestown, and I had the pleasure of witnessing the most satisfactory results, and without hesitation determined to apply the means to the work in hand.

The galvanic battery, which was constructed by Mr. Davis, was one of Dr. Hare's invention, of Philadelphia. It consists of two vessels or jars, each formed by two concentric cylinders of copper, admitting of a cylinder of zinc between. Two copper wires, termed the conducting wires, formed the Imedium by which the electrical fluid was communicated to the charge from the battery. These wires were closely wound with thread, in order to prevent their coming in contact with each other, and both tightly covered with tape, and afterwards served round with twine, thus forming a single coil. At each extremity of the coil the wires were separated for a few inches, like a fork. This form of the galvanic battery, termed by Dr. Hare, the "Calorimoter," is the most simple and portable of any that I have seen; its power for blasting gunpowder may be increased to any required degree, either by enlarging the size of the jars, or increasing their number. We had, in addition to this apparatus, a simple contrivance for proving the charges of powder, which is termed the "Electrometer."

The charges used in blasting consisted of various quantities of gunpowder, according to the effect required, from four ounces to a pound. They were enclosed in perfectly airtight tin cannisters, the smallest being an inch and a quarter in diameter, and the diameter of the largest about two inches; the lengths of the cannisters were eight or nine inches. Two copper wires were introduced into the cannister, about half-way down, with the extremities connected by a fine platinum wire; the other ends of the wires pro

jected twenty or twenty-five inches beyond the mouth of the cannister, which, after being filled with powder, was closed, and effectually secured with a water-proof composition. It will be observed, in thus preparing the charges, that the whole is completely air and water tight, and that no vent to the powder remains, an advantage of which I shall further speak.

The operation of blasting is carried on in the following manner. The hole in the rock for the reception of the charge is drilled to a proper depth by the workmen in the bell; the cannister is then inserted, with the ends of the copper wires extending outside of the hole, which is then filled up or tamped with coarse sand. The ends of the conducting wires are then connected, by means of clamps, to the wires leading from the charge; the other end of the coil is then led up, as the bell is hoisted to the surface, to the battery, which, in all our experiments, was placed on a floating stage directly over the charge. The jars forming the battery are brought near each other, and their whole power concentrated by connecting them together with a short copper wire; the end of one of the conducting wires is then brought in contact with one pole of the battery, and the end of the remaining wire similarly disposed with the other pole, when the explosion instantly follows, by the platinum wire in the charge becoming intensely heated as the electrical current passes through the conducting wires.

We made during the past season nine blasts, with but one failure, which was caused by the platinum wire in the charge becoming accidentally broken, so as to render the electrical circle incomplete; this probably occurred in tamping, an operation which must be conducted with care, as this accident is most liable to be incurred, of all others, owing to the extreme delicacy of the wire. The object of the electrometer is to detect whether this has taken place before the charge is inserted in the rock, and may always be ascertained by a simple trial.

It must be obvious to every one, at all experienced in blasting rocks, that this method has advantages, in many respects, over the old methods, both under and out of water. The danger of accidental explosions is entirely prevented; these occur, for the most part, in the old practice, by carelessness, while in this, great care and nicety are required to produce the explosion. There is very little time required in charging, as the cannister is simply inserted in the hole, and tamped with sand; the whole time occupied in this operation, and making the connexion with the conducting wires, in the present cases, rarely exceeded twenty minutes. There

is great expense and trouble saved in the absence of the train or fuse, which was indispensable in the old methods, especially under water, where was always required a water-tight hose or tube leading to the surface, which was always destroyed by the explosion. Here nothing is lost or injured, except the cannister containing the charge. The explosion of the charge is reduced almost to certainty, and should cases of failure occur, it can be approached with safety, without the suspicion that fire may be near it. The most important advantage, in an economical view, is, that the effect of the charges is much greater than in the old way, in consequence of there being no vent-hole; the whole explosive force of the powder is thus gained, while by the old methods much of it is lost. Our smallest charges displaced a much greater quantity of rock than the same amount of powder by the old means, which we had opportunities of experiencing. With these advantages, this method of blasting places in our hands the most ample means of clearing harbours and rivers of rocks, &c. in any reasonable depth of water.

In using Dr. Hare's apparatus, it appeared that an important advantage was gained over that of Professor Daniell's, employed by Col. Pasley, inasmuch as a very troublesome arrangement, indispensable in the latter, was avoided. This consisted in not being obliged to insulate the conducting wires from the water, as in such a case the connexion of the conducting wires with the charge must be made before the cannisters are placed in the rock; every portion, then, of the wires where the connexion is made must be covered with the waterproof composition. By Professor Daniell's apparatus, it appeared that water was a conductor, thus destroying the electrical circle, if any part of the conducting wires came in contact with it.

Though Dr. Hare's battery was known to Col. Pasley, it was not adopted in his experiments, the reason assigned being that "it did not appear that he had ever used it under

water.'

and making his return by the opposite course to that on which he commenced his tour, he will, on reaching the shore, have enjoyed all the exquisite pleasures attendant on the circuit of about 10,000 feet in distance.

"As a Mercantile Harbour, although we happily do not at present need one, and its appropriation for the purpose might be injurious to the welfare of the town, and prove inimical to the interests of the proprietors of Shoreham harbour and the Railway Company, which (for one) I consider we are in justice bound not to oppose, but on the contrary to support; yet should any fortuitous circumstances ever require its use for such a purpose, it will at all times be a source of pleasure to reflect that you have the means of availing yourself of its resources for the purpose, and having devised means for the transmission of the merchandise unshipped to one or more unobjectionable situations without interfering with the marine drive, the greatest objection to its use as a mercantile harbour may thereby be obviated; and I beg leave to take the liberty to suggest, that in justice to the Chain Pier Company, the use of the breakwaters as a promenade should be a subject of pecuniary arrangement with them, and which, I conceive, it would be to the interest of both parties to endeavour to effect.

"As a Protective Harbour to Fishermen, the cause of humanity, the welfare of a class so numerous and interesting, and the pecuniary interests of the rate-payers are powerful inducements to provide them a haven so beneficial in the hour of danger, so stimulative to habits of industry, from a consciousness on their parts of being able to pursue their calling in dangerous (yet for their purpose the most propitious) weather, having a port of refuge to fly to, from the eastern, western, and southern quarters, in every case of imminent peril.

"Having enumerated, I trust, a sufficient amount of advantages to stimulate you to the endeavour to obtain them, I hope I shall stand excused from entering into a detail of many others that reveal themselves in prospective, and for passing on to

"The Estimate, which, with the able assistance of several competent persons I have been able to arrive at the amount, as well as the insufficiency of data on a work of so novel and peculiar a character will admit; and having made an ample allowance for contingencies, I feel warranted in stating that, I think, the amount will be considerably under 200,0007., one-third of which will be payable for manual labour, a circumstance very far from being unimportant to all those who are interested in the employment of the labouring classes.

"The Testing of the Principle.-The dic

tates of prudence naturally prompt the suggestion, that in case it should be deemed desirable by my fellow-townsmen that so important and great an undertaking should be accomplished, that in the first instance a sufficient number of eminent engineers and competent nautical judges should be consulted as to the probability of the realization of the anticipated advantages, and the practicability of carrying the work into effect; and to facilitate such inquiry, I beg to refer you to the perspective drawing and model which I have caused to be made, and which may be publicly seen at the Town Hall. Should their report be favourable, I beg to submit the suggestion that a subscription should be endeavoured to be raised for the purpose of providing and placing in their designed situations the lighthouse of the southern breakwater, the two adjoining towers, and the two intermediate caissons, as shown by the model, in the following spring and summer, and allow the succeeding winter to pass over in order to test the principle fairly, to ascertain if any improvement can be made in the principle or mode of construction, and to furnish the requisite experience which it may be desirable to obtain, preparatory to the execution of the work to the extent of completion.

"To ascertain the necessary amount to perform this experimental portion of the work, there are the same difficulties in the way as have occurred in making out the estimate for the whole; and as the execution of this minor portion will require nearly all those erections and subsidiary expenses as would be necessary to accomplish the whole, so therefore must the estimate for such portion much exceed the proportionate amount that would be incurred by its execution with the rest. But as such erections will serve their required purpose in ultimately completing the work, such an outlay will not be finally lost, provided it is deemed desirable to finish it. The amount requisite to carry into effect this experimental test, I have reason to believe will not exceed 70007.; but I should suggest that 80007., in 57. shares, be raised, and that such shares should become available, in case it should ultimately be deemed desirable to form a company for the completion of the work, of which the original shareholders would form the nucleus.

"The Execution of the Work.—That in the accomplishment of a work of such magnitude and novelty, many unforeseen difficulties may occur in addition to those which have been already anticipated and mentally provided for, there can be but little doubt; but let them be what they may, I feel assured that in the present day, abounding with so many stupendous and successfully executed projects, that sufficient engineering