phical experiment, and as an elegant mode of procuring immediate light.

A and B are two glass vessels of a spherical figure; A has a hollow tube proceeding from it, an, the upper part of which fits, air tight, into the neck, b, of the other vessel, B; its lower orifice reaches near the bottom of the vessel, B. This tube is encompassed by a plate of zinc, as is seen in the plate. C is a neck from the lower vessel, which joins a brass tube, D, with a stop-cock, d, and a small pipe, c, to direct the hydrogen gas upon the spongy platina which is contained in the copper box, E, joined to the tube of the sliding rod, e. To use it, remove the top vessel, A, fix the plate of zinc round the tube, a a, and pour into the vessel, B, as much dilute sulphuric acid as nearly fills it to the opening, b, after which replace the upper vessel; in this state the acid will act upon the zinc, the water will be decomposed, and the hydrogen being liberated, will rise in bubbles to the upper part of the vessel, B, but not being able to escape at the ground fitting of the part, b, it will press the fluid, and cause it to pass up the tube, a a, and rise into the vessel, A; and this operation will continue till the fluid is depressed as low as the dotted line, g, at which point it will no more act upon the zinc, and no more hydrogen gas will be produced. When a light is required, nothing more is necessary than to turn the cock, d, and allow the gas to blow through the pipe on the mass of spongy platina in the box, E, which will become red-hot, and a match may at once be lighted by it; f is the ground stopper of the upper bottle. The whole apparatus is perfectly free from danger, and forms one of the best and most elegant modes of producing instantaneous light.

BLEACHING.
Art. I.

HISTORY OF BLEACHING.

BLEACHING is altogether a chemical process, and has been much improved in modern times by che

mical discoveries. The great object is, to give the greatest possible degree of whiteness and softness to the different substances of which our garments are made, without injuring their texture. To do this in the best and cheapest manner, it is necessary to know what causes the dark colours of the substances to be bleached, and what substances will act on these colours without acting on the material. It must not be supposed, however, that this art has no other advantage but that of giving a brighter appearance to our clothes. This, though it affords all people a considerable pleasure, is not the only, and, perhaps, not the greatest advantage of bleaching. The dirt, by which garments are rendered unhealthy, is more easily detected in white clothes than in clothes of any other colour. It is also known, that the colouring matter of most of the substances used for clothing is not favourable either to the durability of the stuff, or its health preserving properties; and that at least a moderate bleaching is necessary to make it last long and promote our comfort. We do not say, however, that all these effects of bleaching were known ever since it has been practised; they probably were not, as in its origin, like most of the arts, it was entirely empirical, and practised chiefly on account of the beautiful appearance it imparted to clothing.

The discovery of the most general mode of bleaching, that of wetting cloth exposed to the action of the sun, must have been coeval with the employment of hemp or flax as a material for dress; for it cannot be washed and dried in the sun without becoming sensibly whiter than it was before. Now we learn from sacred history, and the fact is confirmed by mummies brought from Egypt, that the use of fine linen prevailed in that country in the earliest ages of which any record is left. Abraham says to the King of Sodom, "I will not take from a thread of the woof." Rebecca, we are told, covered herself with a veil when she perceived

Isaac (Gen. xxiv. 65.); and Moses tells us that, in his time, the land of Egypt was employed for the growth of flax. (Exodus ix. 31.) A writer of great celebrity, M. Goguet, in his work on the Origin of Laws, says, that the inhabitants of Asia employed earths and alkaline plants in the operations of washing, the use of which continues, at the present time, to form one part of the process of bleaching. In the poems of Homer, the women are described as washing their linen garments and exposing them to the bleaching power of the sun. As early, at least, as 300 years before Christ, lime was employed in bleaching, as we learn from Theophrastus, who lived about that time; and who relates, that a vessel, loaded partly with linen and partly with lime for bleaching it, was burnt by water getting access to the lime. Pliny, an author who wrote in the first century, mentions white linen as being more valuable at Rome than any other. And as linen, at least under the process usually adopted to prepare it, is not naturally white, there is, in this circumstance, strong evidence that bleaching was carried to considerable perfection among the Romans. Indeed, in other parts of his works, he distinctly mentions the several alkaline earths the Romans employed in bleaching. He also says, that both the Gauls and Britons were acquainted with a method of bleaching linen, which he described as being effected by pounding the yarn in a mortar; and, when made into cloth, beating it on a smooth stone with broad-headed cudgels. He adds, it becomes whiter in proportion as it is beaten. It is, perhaps, not a little singular, that beating linen with broad sticks, on flat stones, by the side of a running stream, is, at this day, the mode of washing it through the greater part of Europe. There is, therefore, abundant evidence to prove that bleaching, both by mere exposure to the sun's rays, and by the use of alkaline substances, was practised in the most remote anti

quity. It is here worthy of remark, that alkaline substances continue to be used to this day in bleaching; and it may almost be doubted, if any considerable improvement was made in the art of bleaching, from the time of the Romans till after the discovery of chlorine, or oxymuriatic gas, in 1774. The first introduction of this substance, as a means of bleaching linen and cotton, towards 1787, constitutes an era in the art, since when it has undergone a complete change. Chemistry has now done much to ascertain what are the colouring matters in the different species of natural productions of which clothing is made; and it is enabled, therefore, in a great measure, to prescribe what are the best means of getting rid of the colour without injuring the texture of the cloth.

Before the introduction of oxymuriatic gas, or chlorine, into the art of bleaching, Holland was celebrated throughout Europe for its bleaching grounds; linen was sent there from the farthest part of Germany, and from Scotland, to be bleached, and was then sold at a higher price than could be got for any other linen of an equal fineness. To this day Holland continues to enjoy a reputation; and cloth is sold in all our shops under this name, in consequence of no other country being formerly able to bleach so well. It had some manufactories of its own for linen; but the principal part of that which was exported was made in Silesia, which continues at this day to be the great manufactory for fine linen. So high was the reputation which Holland enjoyed for its bleaching grounds, that they were imitated all over Europe. The great superiority of the Irish linen is supposed to have been principally owing to the Dutch method of bleaching having been introduced into Ireland; and, not thirty years ago, it was thought that an individual conferred a great benefit on the country who established bleaching grounds after the Dutch fashion in the north of Germany, In

our next Article on this subject, we shall describe the method of bleaching which was followed in Holland and other parts of Europe, before the employment of oxymuriatic acid for the purpose of whitening cloth.

ANALYSIS OF SCIENTIFIC
JOURNALS.
ART. II.

ANNALS OF PHILOSOPHY FOR MARCH

1824.

This is a very different publication from the former; and, without costing more, contains a considerably larger quantity of letter-press, and much better articles. There is a due proportion of extracts from other works, , analyses of books, proceedings of philosophical societies, &c. &c., and some original articles. The one on the Crystalline Forms of Artificial Salts, which stands first, we must pass by with out further notice, as being only the end of a series of papers, and without any interest. Then comes "Observations and Experiments on the daily variation of the Horizontal and Dipping Needles, under a reduced power, by Peter Barlow, Esq.," &c., abstracted from the Philosophical Transactions for 1823. This gentleman, who has already contributed so much to extend our knowledge of magnetism, communicated to the Royal Society, in 1823, the result of some of his experiments on the Daily Variation of the Horizontal and Dipping Needles. He thought, and justly thought, that this variation would become greater if the directive power of the needles was diminished. He therefore masked the terrestrial influence, and succeeded in producing, by that means, a much larger daily variation; but he failed, we think, in his hopes of ascertaining, by thus increasing the effect, the cause of this variation. Still, the results he obtained were somewhat curious. He concluded, for example, from the needle generally tending, in whatever direction it might be placed, to some spot between N. and N. N. W., that there is between these two directions a point

where the variation is at zero. Mr. Barlow also observed a curious anomaly between the daily variation in-doors and in the open air; whence he was led to suppose that the solar light is the principal operating agent in producing the daily variation. The third article is "On an improved Apparatus for the Analysis of Organic Products,' borrowed from the Transactions of the Society for the Encouragement of Arts. As the analysis of animal products is at present pursued in various parts of Europe with great activity and some curious re-, sults, we shall take an early opportunity of laying this paper, with its accompanying plate, before our readers. At present, we must content ourselves with having referred to it. The fourth article is is "On the ancient Tin Trade," from which we learn that the writer differs from the Rev. T. Hodgson, in his notion that the Phoenicians had traded to Cornwall for Tin sixteen centuries before the time of Julius Cæsar. We willingly leave these antiquaries, learned in the lore of other times, to settle this point betwixt them. From the next article, "On Fossil Shells," also borrowed from the Philosophical Transactions, we learn as little le of what Nature was doing some forty or fifty centuries ago, as we learned from the former article of what the good people of Cornwall and the Phoenicians were about at a later period. The paper is, however, from a learned F.R.S., and of course must be of great value. Wei necessarily pass over article sixth, "On the Active Power of Dilatation of the Heart, by D. Williams, M. D.;" for the phenomena of life, though the living principle modifies chemical action, and though many of its results are obtained by chemical processes, are not to be wholly explained by chemical laws. The next article is for the adepts of chemistry, being a Table of Equivalent Numbers, drawn up by the Editor. be useful to Chemists, but neither of extract nor further description. We have e then Astro

67

nomical Observations, by that indefatigable friend of science, Col. Beaufoy. In article nine, G. Cumberland, Esq., gives his opinion as to the cause which has brought together the bones of various animals in caves; to account for which, we agree with him, will be a subject of some difficulty. We have then a Table of the Comparative Temperature of Penzance and Pisa, for one month, by Mr. Edward Giddy; and if this short period of observation entitled us to draw any inference, we might conclude that Cornwall was quite as warm in winter as this part of Italy, and subject to less sudden variations of temperature. The mean of the whole observations at the latter place was 39° 9'; at the former, 39° 8'; the greatest difference betwixt the mean of three observations, for any two days, was, at the latter, 21° 0'; at the former, 20° 6′; the difference betwixt the lowest and highest temperature observed in the whole period at both places was in the same ratio; but the difference betwixt any two consecutive observations, amounted at Penzance only to 6o 1', while at Pisa the difference was as much as 1597. Article eleven is an account, taken from the French, of the "Volcanos at present in existence;" in which it is stated that, with the exception of two in the central part of Asia, not one is more than 50 leagues from the sea: whence it is inferred that water acts an important part in volcanic eruptions. The following general summary is worth quoting.

Number of Active Volcanos.

heads. Mr. Smith, F. R. S., afterwards proves, in a paper concerning Jupiter's third and fourth Satellites,that the opinion of its being of no use to make observations on these bodies, originates in prejudice and terminates in error. The ANNALS coneludes with an analysis of books, in which we observe an account of some curious results obtained by Mr. Scoresby, as to magnetism. This gentleman has found that the magnetizing effects of percussion might be increased by hammering on the end of a steel bar, while its lower end rested on the upper end of a large rod of iron or soft steel. This effect was increased by hammering the wire or bar of steel between two bars of iron; and, treated in this way, the bars were speedily made so magnetic as to lift their own weight.

AIR BEDS.

DREAMS, as all the world knows, are only phantoms of the brain; and it is likely they will be rendered more pleasing by sleeping on air beds. An ingenious mechanic, of Somersetshire, not long ago obtained a patent for stuffing a bed with air instead of feathers; and the following is the description of this new mode of obtaining light sleep: The invention consists in rendering the case of the bed, pillow, &c. impervious to air, and filling it, by means of an air-pump, (we presume a condensing syringe is here meant) with common atmospheric air, instead of down or feathers. The air is introduced through an aperture or tube into the case, and prevented from returning by means of an air-tight stop-cock or valve. The case may be rendered impervious to air by various methods; but that recommended by the patentee, is a composition of India rubber, spirits of turpentine, and linseed oil, which, when dry, is extremely pliable, and so elastic, that if the cloth be folded in sharp corners, it will not crack or peel off

"The advantages of this method of construction for beds and pillows, are their superior degree of