on the earth successively, that they lived and worked here for indefinite periods, and then vanished, and made way for other kindred generations. The most distinguished student of animalculites is EHRENBERG of Berlin, who is the Lord Rosse of the microscope. These tiny animals exist in ten million times ten millions, and millions of millions, and are found living in all water and liquids. Wherever you see a spot of yellow or ochreous scum in a pond, or ditch, or any stagnant water, that scum consists of an aggregation of hosts of animalculæ. The living thing itself that is called an animalculite, or an infusorian, is a soft, juicy, fleshy, or mucous substance, that, for the most part, lives in a case which forms its house and home. This case is sometimes called its shield and sometimes its shell; and by technical writers it is called the carapace. Some, however, exist without such cases, but are naked and have a flexible skin. The cases or shields of animalculites differ in different species. In one class, the shields are calcareous or limy; in others siliceous or flinty; in others, ferruginous or irony. Their forms and shapes are innumerable, but frequently of great beauty and symmetry. The Xanthidia are a hollow globe of flinty matter. The Pyxidiculæ have a case like a saucer which is filled with their body. The Bacillaria look like a dozen cards placed in zigzag row, one touching the other at a point. The Naviculæ have a bivalve shell with six openings. The Gaillonella have a bivalve case, but of a cylindrical and half globular form. You will find the rich and beautiful variety of their shapes well illustrated in Dr. Mantell's "Medals of Creation," and especially in his "Invisible World. It is these shields or cases of the animalculite, and not the animalculites themselves, that claim the attention of the geologist, for it is these shields that he discovers mineralised, and which, in a fossil state, constitutes vast rocks in the crust of the earth. Ehrenberg has found them in flint, in opal, in chalk, and in many other rocks. They are found in vast profusion in rocks of different periods-such as the tertiary series, and in the chalky and other secondary deposits. Fossil animalculites are those which had shields; for the races that were naked and had a flexible skin had nothing enduring in their structure. Our lesson will embrace not only the fossils which belong strictly to the infusoria, but also other minute organisms with which they are associated. One class of these are called Polythalamia, because their shells have many chambers in them, and are not like that of the snail, which has only one. The other are called Foraminifera, because their cases or shells are covered with pores, or because the different chambers of their shell are connected by a pore, and not by a siphuncle that runs through each. ANIMALCULITES IN SOILS AND SANDS. At the bottom of many swamps and peat bogs, whether resting on modern soils or on ancient rocks, there are generally found layers of white, marly, or flinty paste or clay. This paste or clay is made up entirely of the shields of infusoria, They are found in abundance under the bogs of Ireland, in Lough Island, near Newcastle, and in many parts of North America. This statement refers to peat bogs of the present age; but when we examine the deposits of the tertiary period, the animalculite relics far surpass, both in multiplicity of forms and in extent of distribution, any infusorial strata of modern times. And even the profusion which is found in the tertiaries of England is not to be compared with those of the continent, such as France and Germany, and also those of North America. The rocks of the Paris basin abound with marine sands. These sands are so full of microscopic animalculites, that a cubic inch of them—that is, a mass cut and squared like a dice an inch each way-would contain sixty thousand Foraminifera and Infusoria. This is particularly the case with the sands brought from Grignon in that neighbourhood. In the district of Bilin, in Northern Germany, there is a rock cailed “polishing slate." The rock is of considerable extent, and is fourteen feet in thickness. It consists entirely of the flinty shields of Gaillonellæ. These shells are so minute, that a cubic inch of the slate contains forty-one thousand millions, 41,000,000,000 of animalculites. in Lapland there is a rock of fossil flour, which is called Bergmehl, or mountain meal. When bread is scarce, the inhabitants mingle this fossil meal with the flour of corn, or with meal made of the bark of trees, ground for food. This Bergmehl, or fossil flour, is one mass of animalculites. The same kind of rock is found at San Fioro in Tuscany. In the neighbourhood of Eyra, in Bohemia, there is dug up a fine white earth, which lies about three feet under the surface. When this earth is dry, it has all the appearance of pure magnesia; but when it is examined by the microscope, it is seen to be formed entirely of an elegant species of infusorial shells called Campilodisca. In North America, one of the most celebrated places for infusorial rocks, is a district that lies between the cities of Richmond and Petersburg in Virginia. The city of Richmond is built on a stratum of flinty marls, having a thickness of more than twenty feet, extending as far as Petersburg, and spreading out into sterile tracts along the sides of the hills. These formations are supposed to belong to the older tertiaries, the meiocene or the eocene. The whole of these deep and extensive marls are composed of infusorial remains. "When," says Dr. Mantell, in "Medals of Creation," p. 225," a few grains of this marl are prepared, and mounted on a glass, almost all their varieties will be manifest, so largely is this earth composed of the skeletons of animalcules: in fact, very few inorganic particles are intermixed with the organisms. The merest pellicle or stain, left by the evaporation of a drop of water in which some of the marl has been mixed, teems with the most beautiful structures." ANIMALCULITES IN CHALK. Few of the revelations of geology have been more astonishing than the discovery, that a large proportion of the purest white chalk consists of minute chambered shells and microscopic corals, all of which are of the most complete and exquisite structure. If you scrape or brush a piece of chalk in water, and examine a small patch of the sediment by a microscope, you will see that it consists of a vast abundance of the cases or shells of Polythalamia, Foraminifera, and Polyparia. Nevertheless, even these microscopic creatures must appear colossal when you think that these animalculæ live upon infusoria more diminutive than themselves. A cubic inch of white chalk contains, according to Ehrenberg, more than one million of well-preserved shells of animalculites. This thought is almost overwhelming, when you consider, in connection with it, the vast extent and the great depth of the chalk formation on the surface of the globe. All the Chalk Downs of England, and the cretaceous rocks of the earth, are only an accumulation of exceedingly minute organisms, which are so closely packed together, that a piece of soft chalk, that you use in making a mark or drawing a line, has half its bulk formed by fossil bodies. This is the case with our English chalk; but in the chalk of the South of Europe, the profusion of animalculite remains is in much greater proportion. There is, of course, in every mass of chalk, a quantity of matter where no animalculite organisms appear in the field of the microscope. This inorganic matter does not owe its ori gin to a precipitation of lime that was previously held in solusion by the water, but it is the result of the attrition and disintegration of the infusiorial organisms into a more pulverized mass of calcareous particles, which have been afterwards reunited by crystallisation. The upper part of the chalk formation abounds in nodules of fiint. Geology has lately shown that these nodules of flints have originated in an accumulation of the pulverised and ground particles which have been derived from the siliceous or flinty shields of animalculites. The late Dr. Mantell distinguished himself much by his researches, chemical and geological, among these infusoria. He says that the most abundant microscopical forms of animalculæ discovered in the chalk and flints of England are two kinds of Polythalamia, called the Rotalia and Texitularia. Associated with these are immense numbers of the class called Foraminifera. These animalculite families are found to be most extensively distributed in the rocks of every part of the globe. In the East, they have been discovered in the Mount of Olives near Jerusalem, in the Plains of Damascus, in the Hills of Autilibanus, and in the rocks about Beyrout. In the South, it has been ascertained that a large proportion of the sand of the Libyan desert of Africa consists of microscopic shells. In North 74 America, the boundless masses of calcareous marls that pre vail in Upper Missouri, and that stretch even to the Rocky A KEY TO THE EXERCISES IN THE Mountains, are, throughout their entire depth and extent, made up of the shells of infusorial animals. FORAMINIFERA IN NUMMULITIE LIMESTONE. Among the lower or older series of tertiary rocks, there are several layers of limestone which consist of minute, flat, and circular pieces that look as so many very diminutive and even microscopic coins. As Nummulus is the Latin for "little coin," this rock has been called Nummulitic, as if it consisted of "fossil money." This calcareous rock consists often of a compact crystalline marble full of nummulites, and these nummulites are only the shells of those extremely minute forms of molluscous animals called Foraminifera. Foraminifera is the Latin for the numerous openings or pores with which the shields of this genera are covered. Nummulites are not all microscopic, though as a genera they are diminutive. If you can imagine the size of a gold penny, or, better still, a gold farthing, you will be helped to conceive of the various sizes of this "fossil money" constituting immense mountains of limestone. The nummulite varies in size from a minute point to a disc of an inch, or an inch anda half in diameter. When you look at it outside, its surface is generally smooth and marked with fine undulating lines; but if the piece be split transversely, it is found to consist of several coils, which are divided into very many cells or chambers, by oblique partitions which have no communication with each other. The extent to which these nummulitic rocks spread in different parts of the globe, has arrested the attention of all practical geologists. In Northern Italy, in a district near Nice, is a rock remarkable for its nummulites. They are also found in the Apennines, on both flanks of the Pyrenees, and among the high Alps. They occur in Asia Minor, and may be traced at intervals along the wide tract of country which extends from the Mediterranean to the borders of Western India. Thick deposits of the same calcareous nature are found in Greece and in Egypt. Sir RODERICK MURCHISON has lately shown in a paper read before the Geological Society of London, that these nummulitic rocks supply one of the chief connecting links between the deposits of India and those of Europe. "They extend," he says, "at intervals through no less than twenty-five degrees of latitude, and near one hundred degrees of longitude: its northernmost ridge on the north flank of the Carpathians being clearly identifiable with its southernmost known limb in Cutch, and its western masses in Spain and Morocco being similar to those of the Bramahpootra" in the East. In the United States, a range of mountains near Suggsville, and which are about three hundred feet high, are entirely composed of one species of nummulites. In our own country, especially in Sussex, the blue clay that is found at Bracklesham and Stubbington, and the calcareous sandstone that is dug up at Emsworth and Bognor, abound in nummulites. The facts which have been briefly stated in this lesson show to you what an important influence the number, the growth, and the decay of minute bodies and invisible agents have had in the slow but progressive formation of our Earth's crust. The contribution of each is almost unappreciable even by the microscope, but the enormous masses produced by their numerical profusion are incalculable. Well might Infinite Power stand over these stupendous operations, and ask "who hath despised the day of small things?" It is by means of these diminutive agents, that He has brought to pass the most astounding phenomena and the most magnificent results. When we think that these minute animalculites have contributed much more material for furnishing the cover of the globe, than have been supplied by lions, and elephants, and whales, and leviathans, we cannot but think of the language of the Psalmist: "O Lord, how manifold are thy works! in wisdom hast thou made them all; the earth is full of thy riches; so is this great and wide sea, wherein are things creeping and innumerable, both small and great beasts. These wait all upon thee, that thou mayest give them their meat in due season. Thou hidest thy face, they are troubled; thou takest away their breath, they die, and return to their dust.” LATIN LESSONS. By JOHN R. BEARD, D.D. Vol. III. p. 72.-ENGLISH-LATIN. Reipublicae interest; meâ refert; illorum interest; omnium interest; neminis refert; se domum reversurum esse certiorem me fecit filius; maritum valere certiorem fecit matrem filia tua; animi sum confusus; mali saepe confusi sunt animi; temporis et necessitatis senatum regina admonet; me suscepti negotii taedet; boni malorum miserentur; illos taedet vitae; te uxorem habere mihi venit in mentem; praeteritorum recordatur; rei militaris es peritus; consciane recti est mens tua? consilii mei te faciam certiorem ; literarum appetens puer fiet sapiens; piscibus scatet mare; mitis est ingenii soror tua; a plurimis divitiae magni aestimantur; quanti hunc librum emisti? non unius assis me faciunt; nostrum est imperare, tuum obsequi; proditionis est accusatus; capitis damnabitur; claves urbis potestatis suae fecerunt hostes. Vol. III. p. 95,-LATIN-ENGLISH. Caesar said to Dumnorix that he pardoned the past misdeeds of his brother Divitiacus; the abandoned woman cursed both; physicians, while they minister to the whole body, cure not even the smallest part; Venus was married to Vulcan; Gabinius is reviled; I have reproved Trebatius because he does not regard his health sufficiently; the unwilling are not easily persuaded; I am of this opinion; a good citizen makes to the republic a present of his private hatreds; the Germans are given to labour and hardships; I am satisfied that you are worthless; a good general is present in dangers; the physician applied remedies to the wounds; Caesar made war on Gaul; certain signs precede certain things; father compares small things with great; the consul preferred the safety of all to the safety of individuals; I set before myself all things; he esteemed his love for his son less than the public good; Quintius Fabius alone survived the slaughter of his family at Cremera; the senate bestowed honours on illustrious men; the virgin married him whom Caecilia had had for a husband; thy keepers have given thee the name of madman; the name of that disease is avarice; my name is Arcturus; I have deliberated and determined; all things belonging to human life ought to have been investigated, heard, read, discussed, and handled by the orator; Alcibiades had such sagacity that he could not be deceived, especially when he purposely kept his mind on the watch; majesty and love do not well agree, nor tarry in one abode; the father gave his son a dog; the Rhine approaches the ocean; you do not know what man you speak ill of; avoid the dog; surely these things do not seem to you suitable to a marriage? the villas, built along the pleasant places of the river, stand on its margin; the world obeys God, and the seas and the lands obey him, and the life of man obeys the commands of the supreme law; I keep constant guard against thee; is agreed between Dejotarus and myself [comma after convenit] that he with his troops should be in my camp; he advised Pompey to fear my house and be on his guard against me; but it is agreed to by all that the Sibyl brought three books to Tarquinius Superbus; it is foolish to allow what you can prevent; neither the plan nor the conversation suits me; an image of victory stood in the right hand of Ceres; the Parthians had taken the standards from Crassus; Caesar betrothed the granddaughter of Atticus to Tiberius Claudius Nero; it is advantageous to the country itself to have citizens who perform what they owe to their parents; no fool nor dishonest person can be well off; Caesar made to his country a present of his grudges; Perseus familiarly smiled on persons whom he scarcely knew; the praise and the glory of other men are commonly objects of envy; you ought to have discerned these things; who has not heard of the watchings (vigiliae) of Demosthenes Plet us always live as if we thought we had to give an account; in the school of Pythagoras silence was imposed on disciples for five years; Aeneas is seen by no one; Julianus and Apollinaris in their lasciviousness and sloth, were like gladiators rather than generals; if my son sins at all he sins against me; we wish to be rich not only for ourselves but for our children, our relatives, our friends, and, above all, for the commonwealth; I recommended peace to Pompey and the senate; who is a witness of this thing? what is Celsus doing, I wonder? what do you wish? I do not understand what is the meaning of avarice in old age; virtue is the only thing which men can neither give nor receive as and nefarious to make a gain of politics; they blame me greatly because I bewail the death of my friend; Pausanias went to assist the inhabitants of Attica; the Veientes go to aid the Sabines; they chose this place as their residence; Caesar left behind five it gift; it is base dilegerunt; tibi subvenit medicus, sed mederi non potest; domo me reliquerunt praesidio; vae mihi! quid facio ? imperio Gallico Italia est adjecta; fratris ingenium longe antecellit meum; si peccas, tibi peccas; cave leonem; portae liber adjacet; copiae fluminis ripac insistunt; mihi convenit liber; hostibus signa detrahent milites; impiis non est bene; mali malis maledicunt; in doctum esse con convenit tibi; prae curru currit equus; bona omnia sibi ipsi proponunt; maximos forti duci honores deferret senatus; volentibus multa facile persuadentur; vulneribus tuis remedia medicus adhibebit; Angli student laboribus; est in periculo pa er (patri est periculum); mulieri supplicanti condonavit; virginem mihi uxorem adjungam. LESSONS IN GERMAN.-No. LXX. Irregular Verbs, continued from p. 33. $ 80. PARADIGM OF A VERB OF THE NEW FORM. Loben, to praise. PARTICIPLE. gelebt haber, to geisht, praised. have praised. $ 81. THE MIXED CONJUGATION (Embracing the Irregular Verbs properly so called). There are a few verbs (sixteen in all), which have, a sort of mixed conjugation: partaking of the Old Form, in that they change their radical vowels to form the Imperfect Tense and the Perfect Participle, and at the same time, partaking of the New Form, in that they assume, in the same parts, the tense-sign te and the participial ending t. These are they which, strictly speaking, are the irregular verbs of the language, and accordingly, they are here so classed. They will be found, also, in the general List of (so called) "irregular" verbs, which, for the sake of convenience, we have inserted. "For there is not anywhere a more miserable being than man among all the creatures that breathe and crawl upon the earth." "And when the early rosy-fingered dawn appeared." JACQUES KNOX: We cannot answer the first query satisfactorily, but can only conjecture there may be some reasons of a local character for using a feminine noun to designate a man. The word des is used with a nominative case in a partitive or indefinite sense to express some, any; as, des pommes, some apples, or simply apples. See vol. i., pp. 32 and 63. We do not know which a in the word amans our correspondent means. A CONSTANT SUBSCRIBER: "Which is the better of the two?" is undoubtedly correct, and best is, strictly speaking, wrong; but it may be questioned whether usage, which is the only guide in language, does not afford the latter sanction enough to render it allowable. TERTIAN: We have not room for the complete parsing of the sentence referred to, nor do we see any difficulty in it. AQUILA PULCHRA: The preposition ab is indispensable before names of living agents, but is not used before those of lifeless instruments, which are simply put in the ablative. Ad insulam could not be changed to insulæ, the dative case. The word to, after a word signifying motion, must generally be translated by ad, followed by an accusative, though the preposition is omitted before the name of a town or small island. The French books mentioned are good and cheap. H. STYLE: We are now preparing an easy German reading book, which will be published soon, under the title of " Lessons in German Pronunciation," We have already published an "Eclectic German Reader," containing select and varied extracts from German authors. Both these works have a dictionary of all the words at the end. BACINE (Manchester): All right.-SALOPIAN (Shrewsbury): We do not know. IGNORAMUS (Amble): Not. ZIG-ZAG (Spalding): His geometrical trisection of an angle won't do; his other queries are exceedingly small.-G. B. (Manchester) is right; he will find the matter put right at p. 89 of the same volume. See the 1st No. of vol. iv.-W. R. C. (Stepney): The Stadium differs in different places and with different ancient writers.-J. C. C.: We really cannot well advise without more definite information; if in town, a personal interview would save immense trouble.-AN ADMIRER: See past Notices to Correspondents.X. Y. Z. (Liverpool): Study Latin well first, and then Greek. UN ELEVE (Birmingham): Here is a French song for you: DODECALOGUE DE L'AMITIÉ. Un ami tu te choisiras Tous tes biens fraternellement. Et faisant ainsi tu seras Sûr d'être aimé bien tendrement. F. H. J. (London) and J. E. H. (Kidderminster): Thanks.-J. DOWELL (Birmingham): Thanks; the cause for a standing army is to keep the balance of power in Europe, as well as for national defence. The second question is absurd.-CRETUS: We don't know the "Heir-at-Law Society."J. RUTHERFORD (Buckden): The correct answer to a question implying an affirmation is yes; and to one implying a negative, is no.-NIL DESPERANDUM asks too much of us.-W. B. HODSON (Lincoln): Series is both singular and plural; hence we can say both this series and these series.— W. W. B. (Taunton) and A FATHER (Burnley): We cannot undertake to recommend one Assurance Society more than another.-C, THOMAS (St. Betting questions.-J. C. JOHNSTONE: We mean that the whole New Austell): Right.-J. THOMAS (Sheffield): We never undertake to answer Testament in French can be had for 6d. The specific gravity of silver, fine and not hammered, is 10-474, and hammered, 10-511; of tin, pure and not hardened, 7.291, and hardened, 7-299; that of water being 1.000. ALPHA (Farringdon): To differentiate y=(1+2)3 (1+x)1, apply the formula dy=d(ur)=udv+vdu, thus: dy=(1+x2)3d(1+x)1+(1+x)'d(1+x2)3= (1+x2)3⁄44(1+x)3dx+ 1+x)13(1+x2)2d(1+x2)= (1+x2)24(1+x2)(1+x)3dx+(1+x2)2(1+x)3(1+x)6xdx= LITERARY NOTICES. FRENCH Now ready, price 4s. in stiff Wrapper, or 5s. strongly bound in cloth, the First Part complete, consisting of the French and English, of CASSELL'S FRENCH DICTIONARY: the entire work will be completed in Twenty-six Threepenny Numbers, and will form one handsome Volume of eight hundred and thirty-two pages. Price 88. 6d. bound in cloth, or the Two Divisions may be had separate. A COMPLETE MANUAL OF THE FRENCH LANGUAGE, by Professor De Lolme, just published, price 3s. neatly bound. This forms one of the most simple, practical, and complete Guides to a thorough knowledge of the French Language which has hitherto been published. The plan upon which it is conducted is admirally calculated to accomplish the proposed object. In the first place, the Grammatical Principles of the Language are clearly laid down, and, secondly, these Principles are copiously illustrated by suitable, Exercises of English to be turned into French. CASSELL'S LESSONS IN FRENCH, in a neat volume, price 2s. in stiff covers or 28. 6d. neatly bound in cloth. A KEY TO CASSELL'S LESSONS IN FRENCH, containing Translations of all the Exercises, with numerous references to the Grammatical Rules, price 1s. paper covers, or 1s. 6d. cloth. GERMAN. CASSELL'S GERMAN DICTIONARY is now issuing in Numbers, at 3d. each Monthly Parts, 1s, each. CASSELL'S LESSONS IN GERMAN, price 28. in stiff covers, or 2s. 6d. cloth. CASSELL'S LESSONS IN LATIN, price 2s. in stiff covers, or 2s. 6d, cloth. CASSELL'S KEY TO THE LATIN EXERCISES, now ready, price 1s. in stiff covers, or 1s. 6d, cloth. LESSONS IN CHEMISTRY.-No. V. ON HYDROGEN. told THE student will remember that in the first lesson he was It has been my especial object to arrange these lessons in such a manner that manipulative details, or the directions for conducting the mechanical part of operations (and chemistry is full of such), may be interspersed with a due proportion of thinking philosophy. I shall continue to hold this object in view, and therefore shall not set off the manipulative part of chemistry by itself, but describe the manufacture of every instrument when wanted. Perhaps the operative student may have observed-at any rate, he ought to have observed, for no phenomenon occurring during the performance of a chemical operation and appertaining to it should remain unnoticed,-I say he may have observed, that during the act of solution of the zinc in dilute sulphuric acid a certain gas was evolved. Now this gas is termed hydrogen; it is the lightest ponderable body in nature, and the common method of procuring it is really that which the student has already followed, namely, by the operation of dilute sulphuric acid upon the metal zinc: iron will answer nearly as well. Perhaps, moreover, the student may have observed that the hydrogen gas thus developed had a peculiar smell; this, however, is a casualty-pure hydrogen is almost devoid of smell. I need not describe on what the smell depends just at this time, further than stating that the cause is a sort of oil generated during the process of dissolving zinc in dilute sulphuric acid. Let us now learn a few properties of this gas by experiment, generalising these properties hereafter. For this purpose, repeat the act of solution,-using zinc and dilute sulphuric acid as before,-only let the solution be performed in the bottle instead of an open dish, and stop its mouth with the perforated cork, armed with its tobacco-pipe shank, immediately after the zinc and dilute acid have been poured into it. It is scarcely necessary to intimate that the mixture of sulphuric acid with the predetermined quantity of water can scarcely, with safety, be attempted in the bottle itself, on account of the heat developed. It requires to be effected in an earthenware basin, jug, cup, or something of that sort. Having generated hydrogen in this way, we shall soon learn one of its most prominent qualities: causing a flame to approach the end of the tobacco-pipe shank, the hydrogen which escapes will immediately take fire, proving that it is combustible. In performing this experiment, it will be well for the operator to place himself at some little distance from the apparatus, because if the light be caused to approach the extremity of the tobacco-pipe shank before the generated hydrogen has forced out all the atmospheric air which the bottle originally contained, an explosion will be the result: not dangerous in itself, but it may be destructive to the clothes by the diffusion of the dilute acid in spray. Every phenomenon, as I have before remarked, occurring during the performance of a chemical experiment is important, and should never be passed unchallenged. In the present case, we do not stipulate for an explosion; we will effect that purposely, and by a convenient process, hereafter. Nevertheless, should an explosion occur, it would only serve to anticipate a communication of the fact, that hydrogen gas forms an explosive mixture when mingled with air in certain proportions. If an explosion occur, replace the stopper, and wait this time before applying the flame until all the atmospheric air has been expelled. This period may be readily guessed at, or may be insured, by giving the operation a little more time. Applying now the flame, the jet of hydrogen will burn tranquilly. The next experiment we will perform shall have reference to the extreme lightness of hydrogen. It is this:-Attach to one end of a thin slip of deal, a drinking-tumbler, or other similar vessel, as indicated in the accompanying diagram at t, fig. 23, and to the other end of the same slip of deal any pan-like contrivance for the suspension of a counterpoise w; next, support the slip by a fulcrum f (an upright board, VOL. IV the apparatus be sufficiently delicate, the tumbler t will be raised, thus proving the levity of hydrogen gas. There are many processes of demonstration more elegant than this: several will be mentioned hereafter. There are none, however, of equal simplicity, as they require the use of apparatus not yet described. The next experiment to be mentioned shall have reference to the products of the combustion of hydrogen gas. For this purpose, ignite a jet of such gas as it emerges from the shank of the tobacco-pipe, and hold over the flame a widemouthed bottle or tumbler, as represented in the following diagram, fig. 24: After the lapse of a few seconds, the vessel, previously dry, will be bedewed with moisture. Where does the student believe the moisture comes from? His first idea, perhaps, might be, that it comes from little particles blown out, as it were, from the liquid in the bottle. În our rough experiment, probably a little is attributable to that source; but if every care be taken to dry the gas, still its combustion yields water-nothing but water. Hence hydrogen derives its name from voup, water, and yivvaw, I form; hydrogen, then, means the water-former. If, instead of a tumbler, the student uses a large-mouthed bottle (a soda-water bottle answers remarkably well), he will generally succeed in eliciting a roaring or singing noise, attributable to vibrations set up in the contained air by means of the burning hydrogen. The chemistry of gases is very delicate; I shall, therefore, when describing these bodies (the term sounds oddly to an unchemical ear, though it is correct) frequently require to mention instruments that the student neither has nor requires to have, a mere description of their form and mode of operation being sufficiently instructive. Of this kind is Cavendish's Eudiometer, the instrument by which the truth that hydrogen by combustion with oxygen (for that is essential) yields water, nothing but water, was first determined. In the experiment which we have performed, the hydrogen supplied itself with oxygen from the atmospheric air; but it would have been com. 84 |