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axiom of “work slowly,” requires to be reversed into “the quicker the work, the better the quality.”

Laboratory apparatus.

Figure I is a plan of the coast survey electrotype laboratory. The glazed partition, b, b, b, b, with a door, d, separates the battery room from the general laboratory, and permits an easy inspection of the batteries, without exposure to their fumes. The laboratory floor is about six feet above the ground, and slopes inward from the sides towards the scuttle holes, h, h, h, h, arranged for discharging the waste liquids spilled upon the floor. To obviate the deleterious effects of working on a floor saturated with chemical agents, when any solutions are spilled, the floor is well flooded and brushed, the water passing off through the scuttle holes. There are four battery cells, placed as indicated, B, B, B, B. A rectangular India-rubber bag, supported by a deep wooden box, contains the battery solutions. Each cell can contain nine silver and eight zinc plates. A metallic connexion unites all the zinc plates of a cell, and another one all the silver plates. Each cell can be used as an independent battery, or two, three, or four cells can be connected in consecutive or simultaneous order, or all combined into two pairs of two in consecutive or simultaneous order, or into one group of three and one of one. The position of the vertical decomposing vat is shown at W, and that of the horizontal vat at H. S is a large tub for washing plates. The tub C contains the solution of chloride of iron. Q is the quicksilver tub, and W, W, are fresh water tubs. F is the furnace, and d, d, c, c, are heating tubes connecting with the vat H. T is a flat iron table. Fig. 2 exhibits a cell and its included plates, with their mode of suspension. Fig. 3 represents the suspending frame of wood and the attached plate, P, prepared for immersion in the vertical vat. Fig. 4 shows the vertical vat and the plates suspended in it. Fig. 5 represents the adjustable plate-supporting frame used in the horizontal vat. Fig. 6 exhibits the interior arrangement of the horizontal vat, a blank plate and an engraved original being in position; also the connecting copper wires leading to the battery. Fig. 7 represents the heating surnace. The door for admitting air is shown at a, and is so connected with an adjusting compound bar of iron and zinc that by an adjusting screw it can be arranged to regulate the draught, opening or closing the door, thus maintaining a uniform heat in the solution. After getting the fire started, this door is set so as to close when the solution reaches a heat of 150°. In principle this furnace is similar to a bath-heater. A tubular helix of lead is coiled within it like the worm of a still, and the terminating branches c and d lead to the horizontal vat, the branch c uniting the top of the vat just below the liquid surface with the bottom of the coil, and d the bottom of the vat with the top of the coil. Hence follows a circulation of the solution from the furnace at top and into it at bottom.

Manipulation.

When a plate is to be electrotyped, it is placed on trestles above the open scuttle holes, h, h, h, h, and thoroughly cleaned by washing with alkalies and acids. It is then silvered, iodized, and placed before a window. A plate of rolled copper an inch larger than the engraved plate is then selected, placed on the flat iron table, and beaten with mallets until a steel straight edge shows it to be plane. It is then weighed and fixed in the vertical plate frame by two copper hooks. The engraved plate is then similarly fixed in a similar frame, when both are placed in a vertical vat and connected with the battery.

The process does not go on well when the plates are vertical, but it is necessary to start the castings in this position to prevent dust, motes, or specks of impurities, from settling on the face. As the rolled plate dissolves, its impurities rapidly render the solution muddy, and endanger the face of the forming plate. For common electrotypes dust or mote specks are not detrimental; but the coast survey copper plates being not inferior in fineness of lines to fine steel plates, the effect of impurities settling on the face of their copies is to give the impressions a clouded appearance. On first immersing the plate, the solution should, therefore, be perfectly clean. Formerly, after each use of the vertical vat, it was emptied and washed out. When the solution had deposited its sediment it was drawn off and strained through very fine cotton. This whole operation was extremely disagreeable, and consumed a whole day of one man.

By a simple expedient I have saved the necessity of cleaning the vat oftener than once a month. To guard the new plate from specks and impurities, a bag of fine cotton is drawn over a slight wooden frame, which keeps it distended. An hour or more before the solution is wanted, the bag, with its included frame, is placed on top of the solution and loaded with the copper bars used to support the plate frames. The weight causes the bag to sink gradually, filtering the contained solution as it goes down. The impurities cannot wholly choke the meshes of the cloth, as a fresh portion is constantly brought into action during the sinking. I thus filter the solution without taking it from the vat or disturbing the sediment, saving much labor, time, and annoyance.

The plate remains in the vertical vat over night, and preparations are made in the morning to transfer it to the horizontal vat. The furnace is first brought into action. A new plate of blank copper, an inch larger than the matrix, is flattened on the iron table, and bolted to the edges of wooden bars by platinum bolts, for the purpose of preventing the plate from sagging downwards when supported horizontally. The plate so arranged is called the strapped plate. The coated matris is then taken from the vertical vat, disengaged from its frame, and arranged in the horizontal frame. A wooden wall, an inch high, then surrounds the plate, and in this wall the strapped plate is laid, when the whole combination is placed in the horizontal vat and the connexion with the battery established. The positive plate is then taken from the vertical vat and its loss of weight noted and recorded. From the known superficial area of the matrix, the quantity of copper required for a casting one-eighth of an inch thick is computed and recorded. The blank copper consumed in both vats must equal this amount before the required thickness is reached, allowance being made for impurities of rolled copper and roughness on the back of the electrotype. After a few hours of action the strapped plate becomes so loaded with impurities that they will begin to drop on the electrotype; this plate must, therefore, be removed from the vat and a new one immediately supplied. The dirty plate is then washed in the large water tub, and when cleaned its loss of weight is found and recorded. By the amount of loss the action of the batteries is tested, and it is found, if Smee's laws are being observed. Vigilance must now be exercised in watching the batteries and rate of work, and the power must be varied to suit circumstances.

The entire working battery generally requires renewal once a day, the process being conducted as follows: One zinc and one silver plate are taken from the battery; the silver placed in the solution of chloride of iron, and the zinc taken to the water tub outside the door of the battery room, where it is scrubbed clean with a hard brush. It is then reamalgamated at the quicksilver tub, and taken back to the battery. The silver plate is transfored from the chloride of iron solution to the adjacent fresh water tub. Another silver plate is then transferred from the battery to the chloride solution, and another zinc cleaned, washed, and put back in the battery with the first silver. In this manner the whole battery can be renewed without sensibly interrupting its action.

When the loss of weight from the rolled copper in both vats indicates that the required thickness of the electrotype is gained, the plate is withdrawn from the battery, detached from its frame, its back smoothed, and its edges filed, until a separation can be made. . By separation, the original becomes liberated, and the alto or reversed relief is silvered and electrotyped exactly as an original. The copy from it, or the electrotyped basso, will, if the process has been properly conducted, be a perfect fac-simile of the original, and in hardness, ductility, and elasticity, will equal the best rolled and hammered or planished copper plate.

Yours, respectfully, GEORGE MATHIOT. Major I. I. Stevens, Assistant in charge of office.

APPENDIX No. 56.

Report of Lieutenant Washington A. Bartlett, U. S. N., assistant in the coast survey, to the Superintendent, on the examination of the reefs in Hell Gate channel, and changes produced by blasting.

New York, December 4, 1851. DEAR SIR: In my previous reports on the improvements being made in Hell Gate channel, by the operations of Mons. Maillefert, facilitated by advances from citizens of New York, I have endeavored to keep you advised of the progress of the work, and its probable effect in im

proving this important channel of ingress to New York harbor. I am now enabled to lay before you results actually obtained, which have substantially improved the navigation of the “Gate;" reduced the risk of passing through it; and which will very considerably modify the sailing directions which appear on the first edition of the coast survey chart of Hell Gate, and its approaches.

Referring to the reports made to you by Lieutenant Commanding Chas. H. Davis, United States navy, on the 15th February, and of Lieutenant Commanding D. D. Porter, on the 30th of October, 1848, the great advantages which they so ably discussed, and so confidently expected would ensue when the effort should be made as proposed, I am happy to say are now being realized.

A close attention to all they suggested as the basis of operations, and the exertions of Mr. Maillefert and Mr. Eben Meriam, based on those reports and surveys, have most conclusively demonstrated to me-so far as the work has progressed—the clear perceptions of those able officers in their suggestions for the improvement of the channel.

It only required Mr. Maillefert's effective method of overcoming the local difficulties involved in any attack on Pot rock to make the work effective. The results are altogether favorable. * *

The first in order, and the principal obstruction in Hell Gate, is Pot rock, on which I found but eight feet of water at low tide; the average depth, however, was about ten feet; the rock at the least depth being about six feet square, deepening to fourteen feet on the east and west sides, and suddenly to four fathoms on the north and south. * •

At half tides the depth of water does not increase on Pot rock, as there is at least a fall of four feet, and a vessel drawing over eight feet must strike upon it. “A full-rigged brig struck it three days since, and went down with a valuable cargo on board.”

This obstruction once removed, Hell Gate would be less dangerous by onehalf, and the eddies, which are now the cause of half the difficulties, would in a measure disappear.”

I have quoted as above Lieutenant Commanding Porter, United States navy, for the purpose of saying that his observations have been most fully sustained by the present condition of Pot rock, and that the vast—I might almost say the incalculable advantages to be derived for all future time from the reduction of this rock, cause it to be considered by all who have occasion to pass through this channel as of inestimable value.

It cannot now be said that a vessel drawing only eight feet of water will strike, for there are not less than eighteen feet water on any part of the rock at low tide; and the prospect is highly favorable to the belief that M. Maillefert will soon have lowered it to twenty feet, a depth which in my opinion is amply sufficient for all the requirements of the Hell Gate channel.

The advantages derived from the increased depth of water on Por rock are as follow:

1st. Vessels drawing sixteen feet water can pass over it with impunity at any time of tide, and any frigate in the navy can do so at high water.

2d. The increased facility for the passage of the rapid current of the flood-tide over the top of Pot rock prevents that high and violent ebul lition of the water which formerly existed to the imminent danger of all small vessels (though they might not hit the rock itself) which were thrown within its influence; while it prevents that rapid eddy, or return current, which formerly existed, and which threw all boats or "small craft" which once entered it into the very centre of the “Pot,” and then engulphed them.

The dangers to be apprehended from these causes (or if averted, encountering others in avoiding them) compelled all mariners to so direct their course through the Gate as to give the “Pot” as wide a berth as possible; and this wide steering again produced other difficulties equally attributable to it, but which otherwise could be easily avoided. Lieutenant Commanding Porter justly said that, “ Pot rock once removed, Hell Gate would be less dangerous by one-half, and the eddies, which are now the cause of half the difficulties, would in a measure disappear.”

The sketches which have been furnished of my examinations of Pot rock, during the progress of its demolition, have shown that it is at a mean depth of twenty feet at low water, one hundred and thirty feet in length, and thirty feet in average width. Before blasting, the least depth extended over å surface six feet square, while the average depth (vide Lieutenaut Porter's report) was about ten feet. With these facts before me, I have estimated that not less than (30,000) thirty thousand cubic feet of rock (hard gneiss) have been broken up, and scattered from the upper portions of the rock, by firing two hundred and twenty sub-marine charges, of one hundred and twenty-five pounds each, without drilling. This is equal to one hundred and thirty-five cubic feet of rock being removed at each blast; which calculation agrees remarkably well with the effect of each blast at Pot rock, and other points where I have examined for facts.

If it had required a pound of powder to a pound of rock, it would be a cheap process at Pot rock; for it is not easy to conceive how this very troublesome obstruction could have been so far demolished by any other mode than that used. The strength of the current is an effectual opponent to any drilling, even supposing it possible, by successfully anchoring a float, the position could be maintained. It was ably attempted and signally failed. The few moments at slack water are not sufficient to find the drilling point, and only sufficient for firing two or three charges, previously arranged for firing, without drilling.

In another part of the report of Lieutenant Commanding D. D. Porter, he states to you as follows: “ There is a small, though very dangerous rock to the southward of Woolsey's bath-house. It extends about fifty yards out into the channel, and is connected with the shore-line at low water. There are three feet of water on it at high tides. On the first of the flood, a buoy, let go opposite «Gibbs's point,' (the southern approach to Hell Gate,) drifted round Hallett's point, between Pot rock and Way's reef, along the edge of the eddies, and over the above-mentioned rock, into • Pot cove. This happens to a great many vessels, and, but for this dangerous obstruction, they would drift into a safe harbor.”

I have now the pleasure to report that this rock, so well described by Lieutenant Porter, and so dangerous that I have seen two vessels bilge on it within a single hour, and still another rock, which, though

leasure to report ous that I have seenhich, though

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