from their relative specific gravities. An account of the condition of the carbon in them, No. 1 and 2, bright grey iron of commerce, while they are the most valuable for construction, are also the most durable: slow cooling and annealing increases the durability. The mode of analysis used by the author is given in great detail, and was approved of by Dr. Ure in the discussion, when he described that which he usually employed. Six equal parallelopipeds of cast iron were immersed for 180 days in sea water slightly acidulated with muriatic acid, frequently renewed; they were removed, and the coat of plumbago rubbed off at intervals of 30 days; the original weight of each piece was 1060 grains, the weight of each specimen after 180 days was 10414 grains, showing an absolute loss by corrosion of 18.6 grains. It is noticed that the Kyanized oak boxes in which the specimens were sunk in the harbour of Kingstown were all perforated two inches through by the "Lymnaria tenebrans," whose ravages are thus proved not to be arrested by Kyanizing. Chilled cast iron is stated to corrode more slowly when exposed to the air only, than that cast in green sand; this is the reverse of corrosion in water. The action upon wrought iron removes alternate portions of the metal, so as with Damascus iron for gun barrels to destroy the electro-positive parts, leaving a grating of minute parallel rays that could be looked through. The finer and more uniform the quality and texture of the iron, the slower is the rate of corrosion. Faggotted bars, and Lowmoor boiler plate, are those kinds which corrode slowest. Hardened cast steel, after" tilting," corrodes least, and low shear steel is destroyed most easily. The author then proceeds to examine the modes of protecting iron by zincing, and says that no mode of coating with zinc appears capable of preserving iron from the action of boiling salt water, but that, on the contrary, the zinc oxidates with unusual rapidity, and the iron is destroyed. He then reviews the causes of destruction of boilers of steam vessels, the results of corrosion of wrought iron in voltaic contact with alloys of copper and tin; and as to the process of Messrs. Elkington for coating iron with zinc, &c., by electro deposit, although he thinks it incapable of resisting any abrasion or even exposure in water for any great length of time, it would be practically useful when exposed freely to the weather, and for architectural purposes it would be very valuable. He then goes to the subject of the durability of iron ships, and after arguing carefully all the causes of their probable decay, and explaining a multitude of interesting facts relative to them, he arrives at the conclusion, that if the proper means be adopted for guarding against or reducing the rate of corrosion, and the amount of fouling by adherent marine plants and animals, in future iron vessels may be rendered as much safer and more enduring than those of timber, as the steam ships of the present time are superior to the vessels two centuries past. The full details are given of all the principal modes of preserving iron, and particularly those invented by the author, which consist first in coating with zinc; then a varnish, of which the basis is asphaltum; and then a poisonous paint to prevent the adherence of marine plants and molluscous animals. In the

discussion which ensued the author's plans and observations were fully approved; and in support of the durability of iron vessels, it was stated that iron canal-boats, which had been made forty years since, were now in use in Staffordshire; and that the "Aaron Manby," which was built in 1821, and was the first iron steamer ever sent to sea, had been constantly in use up to the present time without requiring any material repair.-Illustrated Polytechnic Review, No. 22.

DANIELL AND HUTCHINSON'S NEW MANUFACTURE OF LIME. MESSRS. DANIEL and HUTCHINSON have discovered that there are large tracts of sand on the coasts of this kingdom, and particularly on the coasts of the county of Cornwall, which are at present either treated as valueless, or made use of, like other sand, for purposes of mechanical intermixture merely, as in the making of mortar, breaking up of tenacious soils, &c. ; but from which, nevertheless, Lime of an excellent quality, applicable to building, agricultural, manufacturing, and other purposes, can be manufactured in large quantites. The patentees state that they have ascertained, " by numerous and careful analyses of the sand referred to, that it usually contains more than 70 per cent. of carbonate of lime." The mode of reduction which they adopt is thus described :-"In the first place, in order to test whether the sand on which we propose to operate is of the proper quality, we put an ascertained quantity into a retort, and pour dilute muriatic acid upon it; if it contain carbonate of lime, a violent effervescence ensues, and carbonic acid is rapidly evolved (the presence of which may be readily detected by its reddening litmus paper). We then neutralize the muriatic acid by the addition of liquid ammonia, and precipitate the lime by adding the carbonate of ammonia in excess. We next weigh this precipitate, which gives us a measure of the average quantity of lime which may be extracted from larger quantities of the sand of which that experimented upon was a sample. If the weight of the precipitate is from six to eight tenth parts of the original weight of sand tested, then the sand is of a proper quality for the purpose of our manufacture; but if much under that, the product will in some places not be sufficient to defray the expenses of reduction. In manufacturing the lime on a large scale, we proceed as follows:-We make use of reverberatory furnaces, varying in size according to the quantities operated upon, but the bodies of which are generally from 20 to 30 feet in length, from six to ten feet in their greatest width, but gradually contracted towards the end, where they open into the chimney, and from 15 inches to 2 feet in height. The sand is laid upon the bed of the furnaces to the height of the bridges, which are made a little higher than usual, in order that they may protect the sand from being blown forward by the direct action of the current of flame upon them. The high degree of heat to which the sand is here exposed expels the carbonic acid so quickly, that in about two hours the process of conversion is generally perfected. The lime is then withdrawn from the furnace through doorways made at intervals, either in the sides, end, or bottom, for that

purpose. It is now in a proper state to be employed as a manure; but to fit it for the various other purposes to which it may be applied, we first pass it through fine sieves to separate any extraneous substances which it may contain."

When it is desired to convert the lime so obtained into hydrate of lime, the patentees add the necessary equivalent of water; if into sulphate of lime, or gypsum, they add the necessary equivalent of sulphuric acid; and so on through all the various combinations of which lime is susceptible.-Mechanics' Magazine, No. 1059.

AMERICAN EXCAVATOR.

THIS machine, constructed by Carmichael and Co., for Excavating Earth-work, has received in America the appellation of "The Yankee Geologist." The machine is composed of the following parts, namely, a strong wooden platform, mounted on wheels, which run on a temporary railway; second, a powerful crane, firmly fixed at one end of the platform; third, on the other end of the platform, a steam engine, which actuates the machinery; fourth, a shovel, scraper, excavator, or digging tool, which is suspended by a strong chain from the jib of the crane, which chain passes over pulley wheels, and thence round a drum connected with the machinery; and lastly, the arrangement of wheelwork necessary to produce the various evolutions and motions of this novel machine. As to the quantity of earth excavated in a given time, it may be stated that 30,719 car (waggon) loads, each containing 1 cubic yard of hard excavation, consisting of clay, sand, coarse gravel, and boulders of various sizes, some of them closely bedded together, and many of them requiring blasts to cause their displacement, were excavated in forty-six days.

NEW LIGHT.

It is now four years since the first experiment on the subject of rendering continuous, and fixing at a given point, the electric fluid, and making it applicable to the general purposes of lighting, was made at Paris; but the discoverer was not able to induce any person to advance even 1,000f. for an apparatus on a sufficiently large scale for a public experiment. A public experiment has, during the past year, taken place at the Place de la Concorde. On one of the bases of the statues called the Pavillon de Lille, a glass globe of apparently twelve or thirteen inches diameter, with a moveable reflector, was fixed in connection with a voltaic battery, and at a little before nine o'clock the electric fluid was thrown into it by a conductor. At this time, all the gas lights in the place, about 100 in number, were burning. As soon as the electric light appeared, the nearest gas lights had the same dull, thick, and heavy appearance as oil lamps have by the side of gas. Soon afterwards, the gas lights were extinguished, and the electric light shone forth in all its brilliancy. Within 100 yards of the light, it was easy to read the smallest print; it was, in fact, as light as day. The estimate made by scientific persons, who were present, was, that the electric light was equal to twenty of the gas lamps, and conse

quently that five of these lights would suffice to light the whole place most brilliantly. There would also be another great advantage in the electric light. It gives out no bad smell; it emits none of those elements which, in the burning of gas, are so injurious to health, and explosion would be impossible. The only danger that would arise would be at the battery itself, but that would be under the control of competent persons; and even in this respect there would be no danger, even to unskilful persons, with an apparatus of moderate size. Internal lighting would be as practicable as external lighting, for, by conductors, the fluid would be conveyed to every part of the house. This experiment was with a voltaic battery of two hundred pairs, composed as follows:-1st, an outer globe of glass; 2dly, in this globe a cylinder of charcoal, open at both ends, and plunged in the nitric acid contained in the outer globe; 3dly, in the cylinder of charcoal a porous porcelain vase, containing acidulated water (with sulphuric acid)— this replaces the cloth in the common battery; 4thly, in the porcelain vase a cylinder of amalgam of zinc plunged in acidulated water. The pile was on the Pavillon de Lisle; the two copper conductors from the two poles, and pointed with charcoal, lead to an empty globe from which the air has been exhausted. The two fluids on meeting produce a soft but most intense light. The strength of the electric light did not appear to exceed that of the hydro-oxygen; but then how much more simple is the apparatus; how much less costly the expense of production! The hydro-oxygen light requires a double and most expensive apparatus, and is only applicable to a few localities; the electric light may be applied externally and internally in any place.— The Builder, No. 39.

AMERICAN REFLECTING LANTERN AND HELIOTROPE.

THIS Lantern was constructed by Messrs. Henry N. Hooper and Co., of Boston, under Major Graham's directions. It was similar in form to the Parabolic Reflector Lantern, sometimes used in lighthouses, but much smaller, so as to be portable.

The burner was of the Argand character, with a cylindrical wick, whose transverse section was half an inch in diameter, supplied with oil in the ordinary manner. This was placed in the focus of a parabolic reflector, or paraboloid, of sheet copper, lined inside with silver about one-twentieth of an inch in thickness, polished very smooth and bright. The dimensions were as follows:

Diameter of the base of frustrum of reflector..
Distance of vertex from base..

Inches.

16.

3.75

Distance of focus from vertex

2.25

Diameter of cylindrical burner..

-50

Diameter of a larger burner, which was never used,
but which, by an adapting piece, could be easily
substituted

1.25

The instrument answered the purpose for which it was intended, admirably well, and was of great use in tracing the due north line. While it occupied the station at Park's Hill, 15 feet above the surface of the

ground, or 828 feet above the sea, in the latter part of September, and early part of October, 1841, the light from it was distinctly seen with the naked eye, at night, when the weather was clear, from Blue Hill, whose summit, where crossed by the meridian line, is 1071 feet above the sea; the intervening country averaging about 500 feet above the sea, and the stations being 36 miles apart.

The light appeared to the naked eye, at that distance, as bright, and of about the same magnitude, as the planet Venus. Viewed through the transit telescope, of 43 inches focal length, it presented a luminous disk, of about thirty seconds of arc in diameter. From its brilliancy at that distance, Major G. has no doubt that it would have been visible to the naked eye at 50 miles, and through the telescope at 100 miles, could stations, free from interposing objects, have been found so far apart.

It was remarked, that the wick employed by Major G. was considerably smaller than that usually made, even for polar lamps; and to this cause he attributed, in a great measure, the perfection with which the parallel rays were transmitted from the reflecting parabolic surface, so as to make them visible at so great a distance. Though a greater quantity of light is generated by a larger wick, the portion of rays reflected in a direction parallel to the axis, and which alone come to the eye, is the smaller as the flame transcends the focal limit. The size of wick most advantageous for use may easily be determined by experiment: Major G.'s impression is, that the smaller its transverse section, provided it is only large enough to escape being choked up by the charred particles, even one-third, or perhaps one-fourth, of an inch, the farther the light would be visible.

It has occurred to Major G. that lanterns of this description might be used with great advantage as station-marks, in extensive trigonometrical surveys, requiring primary triangles of great length of sides. A revolving motion might be given to the lanterns, so as to make the light transmitted from them visible from many different stations within short intervals of time. Their simplicity, and the ease with which they are managed, would perhaps give them, for such purposes, a great advantage over the Drummond, or Bude, lights, even though they be not so brilliant as the latter.

The helitrope, which he employed in the day-time, was made by order of Mr. Hassler, at the instrument shop of the coast survey office. It was a rectangular parallelogram of good German plate glass, 1 by 1 inch in size, giving an area of reflecting surface of 216 square inches. This also was seen at the distance of 36 miles.Proceedings of the American Philosophical Society.

DR. URE'S REPORT ON THE BUDE LIGHT.

FROM the Report of a Committee of the House of Commons, it appears that this light is so called from Bude, in Cornwall, the residence of its inventor, Mr. Gurney-a name bestowed upon it at the Trinity House, to distinguish it from the ignited lime light, which he first described in his work on chemistry, in the year 1823.