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That they have allowed him to It has been long known, that make this discovery is, in fact, a when a magnetized needle is freely proof of their carelessness. For suspended, it only preserves itself 600 years have they made use of in a horizontal position in a small the compass; day after day have zone near the terrestrial equator. they found its indications wrong, To the south of this the south end and been obliged to imagine of the needle dips or inclines to strange currents in the ocean, or the horizon; and to the north the suppose an up bill and down hill at north end dips or inclines. This sea, to account for the ship's run- is owing to the magnetic attraction ning ashore, or reaching spots from of the earth. It has also been long which, judging by their compass, kuown, that the upper ends of all they ought to have been far away. iron bodies attract the north end of Notwithstanding frequentand enor- such a needle in northern, and the mous errors of this kind, causing a other end in southern latitudes; great loss of ships and valuable and the lower ends of all iron bolives, so careless or so confiding dies have an opposite effect. It is have they been through all these now known too, from experience, 600 years, that, as far as we know, that when the ship lies with her no one of them ever seems to have head and stern north and south, thought their compass was some- or in a line with the magnetic metimes a faithless guide. In 1794, ridian, that these two attractions Mr. Downie, master of his ma- are either coincident or directly jesty's ship Glory, was the first to opposite, and have no effect on the remark, that the “ quantity of iron lateral direction of the needle ; in ships had an effect in attracting but when the ship's head is turned the needle.” Capt. Flinders traced towards the east or the west, the its connexion with the dip of the needle, owing to the effect of these needle; but the matter was again two opposite forces, namely, the forgotten, till Mr. Bain, another magnetic attraction of the earth master of the navy, published, a and the attraction of the ends of few years ago, his valuable “ Trea- the iron bodies in the ship, no longer tise on the Variations of the Com- points north and south, and its vapass.” This fixed attention; and riation will depend on the resulting Captains Parry and Ross being action of both the magnetic attracdirected by the Admiralty to make tion of the earth and the iron of observations on the subject, during the ship. This variation, when not the voyage to the North Pole, it taken into account, as it never was was found that the compasses were, till now, makes the course of the on some occasions, upwards of 500, ship, as shown by the compass, or more than the eighth of a circle different from her real course. It wrong. This effect was certainly depends, too, on so many circumnot so great formerly as at present, stances, such as difference of place, owing to the greater quantity of difference of direction of the ship's iron now used in constructing and head, and the quantity and posi. ballasting our ships. The great tion of the iron in her frame, as pitch, however, to which it has now almost to bid defiance to calculaarrived, called for a prompt and tion. The first additional fact Mr. efficacious remedy, or there could Barlow seems to have ascertained be no security for sailors: Mr. was, that the points in all bodies of Barlow set himself to this task and iron, situated between their upper succeeded. We shall not follow and lower ends, which had no effect this gentleman through his ingeni- on the needle, were all in the same ous experiments and his mathema- plane, and this plane formed with tical demonstrations, but endeą. the horizon an angle equal to the

vour to give our readers a plain complement of the dip descending .. account of the cause of the incor- from the north towards the south. . rectness of the common compasses, The needle of the mariner's comand of his remedy.

pass is suspended horizontally, or

is not allowed to dip; and Mr. iron ought to be placed, as to the Barlow found that the same fact compass, in every ship, in order to was true of such needles, as well as correct the local attraction. Tables of dipping needles. It was before will ultimately be calculated, howknown, that a large mass of iron ever, so as to make this unneces. attracted more powerfully than a sary. The plate may be placed smaller mass, and that the power either before or abast the compass; varied inversely as the cube of the in the former case doubling the distance; Mr. Barlow has, how- effect of the attraction, in the latter ever, shown, which fact is very ex- neutralizing it. The former is bet* traordinary, that this power resides ter for southern voyages, the latter wholly in the surface of the iron, for high northern latitudes. The and is the same in a hollow shell, plates vary from 12 to 16 inches in the substance of which is not one- diameter, and, in fact, the instrutwenticth of an inch thick, as in a' ment has hitherto been made of solid ball of the same circumfe two plates screwed together. They rence.

have a hole in the centre, through These discoveries were applied which is passed a brass socket with as follows:+It is plain, that in a broad bead, having an exterior such a mass of iron as forms part screw, with wbich the two plates of a ship, by far the greater part is and an interposed piece of wood of neutralized by opposite actions, the same size are strongly screwed and that all the effect may be re- together, the board being intended ferred to one single point of the to increase the thickness without vessel; and this point, as regards adding to the weight. The several the ship, will be the same in all parts of the plates are represented parts of the world. But as the sur- in Figs. 1 and 2, and Fig. 3 shows face of iron only possesses mag- the brass pin, socket and pedestal, netic power, it must be easy to and the whole combined, as in action procure a plate of iron of inconsi- 'on ship-board. We have only to add, derable weight, which, when placed that this apparatus has been tried Dear the compass, shall counter- in several of his Majesty's ships balance the iron of the ship. The with the greatest success. In one first thing to be done is to ascertain instance, reported by Lieutenant the local attraction of each vessel. Mudge, the situation of the ship, The ship being so moored as to admit after a run of 183 miles, as pointof her head being directed to eached out by the common compass, point of the compass successively, differed 19 miles in latitude, and and there steadied, the bearings of 32 in longitude, from her true situsome distant object are to be taken ation. On trying the compass by round the whole circle. These Mr. Barlow's corrected one, it was bearings will vary from each other found to be wrong 70; and when according to the attractive power this correction was applied, the of the vessel; and it will be found situation of the ship, as indicated that two of them, taken while the by the compass, differed from hership's head was directed to oppo- true situation only two miles of site points of the compass, nearly latitude, and four of longitude. agree. The mean of these two is We are quite sure that our readers, considered the true bearing; and by whether they are animated by pathem also the line of no attraction triotism, or soothed by the more in the vessel, which is generally gentle feelings of humanity, will straight, fore and aft, is known. forgive us for occupying so large By then comparing the true bear a portion of our space with the deing with the bearing found at every scription of a simple instrument, point of the compass, the local at- which, we conceive, will be to traction at every one is found. sailors what Sir Humphry Davy's Hitherto it has been a matter of safety-lamp is to miners. Before experiment on shore, to determine they possessed these, they could the situation in which a plate of descend into the mine or sail over

the ocean; but now alone can they mineral of fine ažure colour, from do either, with an instrument in which ultramarine is prepared. their band that warns then when the finest specimens are brought danger 'is near, and shows them from China, Persia, and Great Buhow to avoid it.

charia.

BALANCE. În chemistry it is es

sential to have the weighing maDICTIONARY OF CHEMISTRY.

chine perfect, particularly as not Aubier, alburnum. The layer of a few important theories on the wood in trees next the bark, so composition of bodies are formed named to distinguish it from the from the weight of their component more perfect wood, which is harder parts. For this purpose analytical. and browner.

chemists employ very delicate in-. AURIPIGMENTUM, yellow orpiment. struments. Ramsden lately made A mixture of arsenic and sulphur. a balauce for the Royal Society,

AURUM FULMINANS, fulminating which turns on steel edges placed gold.

on planes of polished crystal. It is AURUM GRAPHICUM, An ore of said to be sepsibly affected by the tellarium.

seven millionth part of the weight AURUM MUSIVŮM, musicum, mo- it is capable of weighing. saicum. A combination of tin and BALAS RUBY, spinelle. A presulphur, the proportions of which it cious stone of red and blue, or is not necessary should be deter- brown colour. " minate. It is used as a pigment to BALDWIN's PHOSPHORUS. Ignited" give a gold colour to statues made nitrate of lime, of plaster of Paris, and also mixed BALLOON. In chemistry, a rewith melted glass, to produce an ceiver of a spherical form. In Aeroimitation of lapis lazuli.

statics, a silken bag employed to AURUM PARADOXICUM. An ore contain air of a less specific graof telluriam; all these ores contain vity than the atmosphere, and cona greater or less quantity of gold, sequently to rise from the surface and hence their name of Aurum.. of the earth.

AVANTURINË. A species of quartz BALM OF Gilead, (not Dr. Solo- rook, containing spangles of mica. mon's) opobalsum. A balsam ob

AXE-STONE. A mineral, so named tained from the amyris Gileadensis, from being worked into hatchets a tree which grows in Arabia, par." by the New Zealanders. It is a ticularly near Mecca. It is highly species of jade, and is found in valued by the Turks, and seldom Corsica, Switzerland, and other or never met with among Chris;": parts of Europe, as well as in New tians. Zealand....

AZOTANE, chloride of azote.

Azote, nitrogen, corrupted air,' LUMINOUS PLANTS. ; tritt mephitic air, phlogisticated air. An. Potatoes kept in a cellar in a elementary substance, forming growing state sometimes become a about four-fifths of the atmosphere, so luminous that we can read prints and entering largely into the com- by their light. The dictamnus albus-ban position of all animal bodies... white dittany, spreads around it int si , DEUTOXIDE or, nitrous dry summer evenings an atmo- of

sphere which, when a taper is 15 - , PROTOXIDÉ Or, gaseous brought to it, burns with a brighted · oxide of azote.

blue flame. Some plants give outoa AZÓTIC GAS. The gas of which a sparkling light, probably of the azote is assumed to be the base.' nature of electricity; such is the

AZOTITES, mitrori. The name case with the flowers of calendula given by some chemists to com- (marygold), tropoolom (Indian pounds of protóxide of azot with cress), lilium bulbiferum, and chal, basesse?

114 ? cedonicum (lities), tagetes (French ACUNE-STONE, lapis lazulie 1 A marygold), helianthus (suntłower),

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DEUTOXID

gas.

and polyanthus. Others give out a twenty ounces; distilled water a calm, steady light, of a bluisht, pint and a half. First mix the acid, greenish, or yellowish-white colour, with half a pint of water in a glass such as dematium violaceum, Pers. retort, and to the mixture, when schistostega osmundacea, w, and cold, add the muriate of soda; M., philolaca decandra, rhizomor. Pour the remainder of the water pha pinnata, Humb. The luminous into a receiver; then adapting the appearances in the galleries and retort to it, let the muriatic acid shafts of mines are often to be distil into the water from a sand- . traced to rhizomorphous plants.' bath, the heat being gradually The milky juice of some plantsis very raised till the retort becomes red luminous, and when in a state of hot. The specific gravity of muincipient decomposition, branches, riatic acid is to that of distilled trunks, and roots of trees become water as 1.160 to 1.000. One hunluminous.-Edinburgh Philosophical dred and twenty-four grains of Journal.

crystallized subcarbonate of soda

are saturated by 100 grains of this EFFECTS OF SULPHURETTED

acid. HYDROGEN GAS.

Muriatic acid, when perfectly

. pure, is colourless ; it emits white, To the Editor of the Chemist. suffocating fumes, which turn veSir, In vour last Number there getable blues red; and its taste is is a very extraordinary account of very sour and acrid. As it is a discovery, by M.Chaussier, of the usually met with, however, it has fatal effects of sulphuretted hydro- a yellow tinge, which is owing gen gas. What might be its effect either to the presence of chlorine on putting a cat's foot into it. I or peroxide of iron; if the former, never had the curiosity to try, but it may be determined by the smell, that the least quantity of it in or by its power of dissolving gold the air we breathe causes instant leaf; the latter is detected by adddeath, 1 positively deny. I once ing a solution of ammonia, which, inhaled it as I was carrying on a when in excess, throws down a per. process in which a considerable oxide of iron, of a reddish-yellow quantity is disengaged. It pro- colour. Sulphuric acid, which it * duced nothing more than fainting, sometimes contains, is discovered and, as you now see, certainly did

by adding a solution of muriate of not terminate fatally. Either M. barytes to a portion of thc acid, Chaussier has “ put his foot into.it,. diluted with four or five parts of or I have great reason to be thanke distilled water. This dilution is ful that I am not

necessary, because the acid, when July 12. A Cat's-PAW..

concentrated, attracts the water

from a solution of muriate of ba. Is our Correspondent quite sure that what he inhaled was sulphu

rytes, and causing it to crystallize,

gives a fallacious appearance of retted hydrogen? No doubt has hitherto been thrown on the accu

the presence of sulphuric acid.;'

Phurmacopæia Londinensis, Phillips's', racy of M. Chaussier's statements, Trans and he enjoys a considerable repu.. tation. We should be glad, therefore, if our Correspondent would INODOROUS HYDROGENdescribe the process he alludes to,

GAS. as the fact he states is of great im.

When hydrogen gas, obtained .. portance.--ED.

from a mixture of iron filings and

diluted sulphuric acid, is passed TO PREPARE MURIATIC.. through pure alcohol, the gas near-. ACID.

Jy loses its odour, and if water be * ACIDUM MURIATICUM. added to the alcohol, it becomes va TAKË dried muriate of soda, two milky. If enclosed in a flask, apd poands, sulphuric acid, by weight, left for some days, an odorous vos

latile oil is deposited, which was the workmen say, or by a small contained in the gas, and which portion of it adhering to a flat contributed to its odour. Perfectly piece of glass. It is of a duller inodorous hydrogen gas may be colour, also, when adulterated; it obtained by putting an amalgam tarnishes by long exposure to the of potassium and mercury into pure air, and if shaken in a bottle with distilled water ; but if an acid or water, a black powder speedily muriate of ammonia be added to forms. If Icad be one of the imthe water, which accelerates the purities, it may be discovered by developement of the gas, it agitating the mercury with water, also acquires the same odour as which oxidizes the lead. Pour off that remarked in the solution of the water, and digest the mercury zinc in weak sulphuric acid. This in acetiè acid, which dissolves the odour, therefore, does not belong oxide of lead, and its presence is to the hydrogen gas, but is given proved by its forniing a blackish to it by impurities.-Berzelius. . precipitate with sulphuretted wa

ter. If only a very minute quanTO PROCURE JALAPINE. tity of lead be present, it may be To obtain this new poison, macerate detected by dissolving in nitric powdered jalap for twelve or four- acid; add sulphuretted water, when teen days in acetic acid; a tincture a dark brown precipitate will ensue, is obtained, filter it, saturate it which in a few days will subside. with ammonia, and shake the mix. One part of lead may in this manture violently; à sabulous deposit ner be separated from upwards of will fall, and a few crystals be de- 15,000 parts of mercury. Bismuth posited on the sides of the vessel. may be detected by a solution in Collect both, and wash them in nitric acid prepared without heat; distilled water; redissolve them in pour it into water, when a precipistrong concentrated acetic acid, tate will appear, if bismuth be preand reprecipitate by ammonia sent. The presence of tin is proved added in excess, and small white by adding a weak solution of nitroaeicular crystals are thrown down, muriate of gold, which throws down which are jalapine.

a purple precipitate. Trusting,

Sir, that you may find a corner for ADULTERATION OF MERCURY. these few remarks, I remain MR. EDITOR,As you have in a

Your obedient servant, Jate Number described this sub

PURIFICATOR. stance and its uses, permit me to occupy a corner of your miscellany ACTION OF ARSENIC ON IRON. with a few remarks on its adultera To the Editor of the Chemist. . tion, and the means of detecting SiR, -Having seen the descrip it. There is no substance, I can tion of the phenomenon witnessed assure you, Sir, on very good au- by Arsenicum in the 18th Number thority, more subject to adultera, of the Chemist, I shall answer his tion than mercury. It completely three questions in the following dissolves some of the less costly manner:metals; they pass with it, as you First, The injury sustained by described, through the pores of the melting pot is occasioned by chamois leather, and they even rise the alloy acting on the iron by vir along with it when distilled ; they tue of the great affinity of arsenic are, therefore, very frequently mix- for iron. ed with it in various proportions; Secondly, The action of the alloy and it is very remarkable, that the on the vessel is confined to the mercury will dissolve a greater edge of the melted compound only, quantity of lead or tin, if bismuth because the iron of the cast iron or zing be previously added. This being combined with carbon, its adulteration may be detected by affinity is thereby lessened for the the mercury not being so heavy as arsenic.; but as the arsenic is oxy. it ought to be, dragging a tail, as dated on the surface, its oxygen

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