of the branches. The apparatus being completely filled with columns of mercury and water, if one of the extremities of the tube be put in communication with the vessel of gas or vapour whose tension is to be ascertained, the other extremity remaining open to the free-air, the excess of the pressure in the vessel over Fig. 83. the columns of mercury. This correction will be made by multiplying the preceding product by the fraction, which represents the ratio of the excess of the density of mercury above that of water, to the density of mercury. The doubled tube is made of iron; the second vertical branch open to the air is mounted with a glass tube to show the extremity of the column of mercury; and the scale, which is made of brass, is graduated to atmospheres. Metallic Manometer.-M. Bourdon, a mechanician of Paris, has recently invented a new manometer, represented in fig. 85. be given by the height to which the mercury is raised above the point of departure in the open branch of the tube, multiplied by the number of vertical branches, minus the correction due to the influence of the weight of the intermediate water between This instrument, which is wholly metallic and without mercury, is constructed on the following principle, discovered by the inventor; when a tube having flexible sides and a slightly flattened or oval shape is wound up in the form of a spiral, in the direction of the less diameter, every interior pressure on the sides has a tendency to unwind the tube; and, on the contrary, exterior pressure has a tendency to wind it up. According to this principle, the manometer of M. Bourdon is composed of a brass tube, about 23 feet long, having its sides thin and flexible. A section across the tube, represented at s on the left in the figure, is an ellipse whose greater axis is about of an inch, and smaller axis about of an inch. The extremity a, which is open, is fixed to a tube with a stop-cock d, for the purpose of putting the apparatus in communication with a steamboiler. The extremity b is closed, and moveable like the rest of the tube. Now, when the stop-cock d is open, the pressure which is produced by the tension of the vapour on the interior sides of the tube causes it to unwind. The extremity b is then drawn from left to right, and with it an index e, attached to it, which indicates on a dial-plate the tension of the vapour in atmospheres. This dial-plate is previously graduated by means of a free-air manometer, by putting the apparatus in motion with compressed air. This manometer has the great advantage above the preceding manometers, of being extremely portable and not easily broken. It is now in operation in the locomotives upon several railroads in France. Metallic Barometer.-M. Bourdon is also the inventor of a metallic barometer founded on the same principle as his manometer. This apparatus, represented in fig. 86, is composed of a tube similar to that of the manometer, but shorter, hermetically closed, and fixed at its middle point; so that the vacuum having been made in it beforehand, whenever the atmospheric pressure diminishes, this tube unwinds itself in consequence of the principle above mentioned. The motion is thus communicated to an index which indicates the pressure of a dial-plate. As to the transmission of the motion, it is effected by means of two small wires b and a, which connect the extremities of the tubes with a lever fixed on the axis of the index. If the pressure increases instead of diminishing, the tube will close in upon itself, and there is a small spiral spring at e, which then brings back the index from right to left, under the dial-plate. This barometer is of small THE POPULAR EDUCATOR. size, very sensible, and remarkable for its very great simplicity of construction. Laws of the Mixture of Gases.-When two or more gases are inclosed in the same vessel, their mixture, when not effected by chemical combination, is regulated by the following laws: Fig. 86. All gases which do not act chemically upon each other, when remarked that the mixture acts more rapidly in proportion to the subjected to the same experiment, give the same result; and it is greater difference of densities between the gases. The second law is proved experimentally by the help of the manometer. It Fig. 88. 1st. The mixture, which always takes place rapidly, is continuous and homogeneous, so that all the parts of the whole mass contain the same proportions of each gas. 2nd. The sides of the vessel where the mixture takes place being inextensible, and the temperature constant, the elastic force of the mixture is equal to the sum of the elastic forces of the gases contained in the mixture, when each is referred to the whole mass, according to the law of Mariotte. The first law is a consequence of the extreme porosity and expansive force of gases. chemist Berthollet, by means of the apparatus shown in fig. 87, It was first proved by the French Fig. 87. which is composed of two glass globes, each furnished with a neck and stop-cock, and screwed to each other. The upper globe was filled with hydrogen, of which the density is 0692, and the other globe with carbonic acid, of which the density is 1.529 or 22 times greater than the former. The apparatus was placed in the cellars of the Observatory at Paris, in order to keep them from being shaken, and from every variation of temperature. The stop-cocks being then opened, as in fig. 88, the carbonic acid in the lower globe B, notwithstanding its greater weight, passed partly into the upper globe A, and, at the end of a little time, it was observed that the two globes contained equal proportions of hydrogen and carbonic acid. LESSONS IN CHEMISTRY.-No. XVIII. Consideration of the Results of Combustion in Oxygen Gas.-The experiments performed in our last lesson require that we should now investigate the theory of combustion. We have seen every instance of combustion which has hitherto come under our notice to have been the result, or at all events the concomitant, of the union of the combustible with oxygen as the supporter. In point of fact, almost all instances of combustion are the result of the powerful action of oxygen upon combustibles: not all, however, as was formerly sup posed; hence the definition of combustion, formerly accepted, namely, "rapid union of a combustible with oxygen," is not strictly true. Chlorine, iodine, bromine, sulphur, and perhaps certain other elements, may in some cases take the place of oxygen as supporters of combustion. The only definition of combustion justified by known facts is, "rapid chemical action attended by the evolution of light and heat.' The result of the combustion of substances in oxygen gas may be an oxide, an acid, or an alkali, according to the nature of the combustible. The first and second we have generated form hereafter. in the course of our preceding experiments; the third we shall or bottles in which our various substances were deflagrated, Returning now to a consideration of the contents of the jars let us begin with that vessel in which the iron was burned. You will observe, scattered all over its sides and base, various little globules of a material not unlike iron to look at. If you remove these globules from the vessel, you will find them to be heavy and hard; not unlike the original iron in appearance, but more dull. In reality, they are a compound of oxygen with iron, or, in other words, the oxide of iron, "the black oxide,' as we may call it, by way of contradistinction to iron rust, or "red oxide" of that metal. If you now take one of these little globules, break it on an anvil or stone with a hammer, and strew the particles on litmus paper moistened with a little distilled water, not the slightest effect of redness will be developed on the blue litmus paper. We will therefore take the fact for granted, that the powdered material in question is not an acid-I say, we will take the fact for granted, because, although the reddening of blue litmus paper is a general-it is not a universal test of acidity. There exist certain acids, neither soluble (in ordinary language) nor sour, nor capable of reddening litmus paper; but these are exceptions to a rule. The result of the combustion of iron, then, in oxygen gas is not an acid, neither is it an alkali, as you may demonstrate by comminuting another portion, and strewing it on moistened yellow turmeric paper, or moistened litmus paper previously reddened by contact with an acid. Had the substance operated with been alkaline, the turmeric paper would have been affected with a brown stain, and the reddened litmus paper would have been restored to its original blue tint. Meaning of the term Oxide.-Inasmuch as the result of burning iron in oxygen gas is neither acid nor alkaline, but is nevertheless a compound of oxygen with the iron burned, we call it an oxide of iron. And here you may remember, as a rule of chemical nomenclature, that the term oxide is given to such compounds of bodies with oxygen as are neither acid nor alkaline. Oceasionally the result is of such ambiguous character that one hardly knows what to call it. For example, the substance white arsenic, which has already come under our consideration, was formerly termed oxide of arsenic; it is now termed arsenious acid, because its acid characteristics, although slight, are nevertheless evident. More ambiguous is the socalled oxide of tin, or stannic acid, according to the view we choose to take of it. I allude to the white powder resulting from the action of nitric acid upon tin. Again, in the oxides of alkaline earths we have certain ambiguous results. Lime is the product of the oxidation of a metal termed calcium. Lime is, therefore, treated of as the oxide of calcium; but the oxide is so distinctly alkaline, that chemists also denominate lime" an alkaline earth." You may readily demonstrate this alkalinity of lime by touching a slip of turmeric paper, or reddened litmus paper, with a portion of lime water. The distinctive change of colour due to alkaline re-action will be immediately recognisable. Having examined the solid result of the combustion of iron in oxygen, let us next see whether the gaseous contents of the jar manifest any peculiarity. For this purpose, portions of the gas may be transferred by means of the pneumatic trough, Fig. 1. removed for use, they require no stopper, the thumb being all that is required, fig. 3. Fig. 3. that if one piece of charcoal had been sufficiently small in comparison with the amount of oxygen employed, and sufficiently free from all impure contaminations, it would have entirely disappeared. Do not think, however, that the charcoal has been destroyed-lost by this combustive energy. No element is ever lost. All the fires which have burned since the creation of our globe, all the waters that have ever flowed, all the manifold agencies of death and decay, have not altered by the smallest fraction of a grain the original weight of the world's material elements. Under the three forms of solid, liquid, and gas, they still exist, and must continue to exist to the end of time. The sole result of the combustion of charcoal in oxygen is, then, a gas. Now, consider well the consequences of its gaseous nature. Carbon, you are aware, is especially the combustible of man; either as wood or coal, or charcoal, or oil, or coal gas, carbon, alone or in combination with hydrogen, I repeat, is our chief combustible. Only contemplate what the result would have been, if the product of the combustion of charcoal had been a solid! Just picture to yourself, if you can, the appearance of our world at this late epoch in its history. Every part of it where fire had been frequently lighted would have been covered with a vast heap of stone-like cinders. The product or 'the combustion of charcoal in oxygen being a gas, we must collect a little of this gas in tubes or bottles, and test it methodically. The gas is colourless. Possesses a smell. LESSONS IN GREEK.-No. XXI. The Verb. General Explanations. The Substantive Verb LET us examine the proposition o orparing EσTi ayados, the proposition; that is, it is that of which something is asserted soldier is good. Soldier is what is termed the subject of the or declared. Good is the attribute, or that quality which is ascribed to the subject soldier. And is bears the name of verb; the essential function of which is, you see, to declare or affirm something. The verb is, in union with the attribute, forms The sentence or proposition thus composed may be designated in this manner : Does not support combustion (try by means of an ignited the predicate, and makes a declaration respecting the subject. taper or chip.) Does not burn. Is heavier than the atmosphere. (Demonstrate by two comparative experiments. Fill one bottle and allow it to stand mouth upward unstopped; fill another bottle and allow it to stand mouth downward unstopped; examine both for the presence of carbonic acid gas). Fig. 5. Fig. 5. It reddens blue litmus, and is therefore an acid. Now any colourless invisible gas which reddens blue litmus paper, whitens lime-water, and does not smell like burning sulphur, must be carbonic acid. You will by this time begin to see the reason of our previous employment of certain negative tests. We tested hydrogen gas with lime water, with litmus and with turmeric; we in neither case developed any effect. But we proceeded on the assumption that the gases operated upon were unknown, and we were therefore bound to follow one systematic undeviating course of testing. Instead of a noun, the subject may be a pronoun, viz. eyw, I, nμels, we, &c. As the personal pronoun is not used in Greek, except for emphasis, since the person intended is marked by the termination of the verb, the subject may be involved in and expressed by the verb itself, as Ave, I loose. The verb may also form the predicate of a proposition, and so contain the verb and the attribute; that is, the verb may of itself make the affirmation. Such is the office performed by λvw, I loose. Accordingly, in Greek as in Latin, a verb may contain in itself the subject, the verb, and the attribute; in other words, it may comprise both predicate and subject, as ypupw, I write. Here we have a verb in three forms; the first form is called the active voice, the second form is called the middle voice, the third form is called the passive voice. Those verbs are active which simply express action. Those verbs are middle of which the action comes back on the subject. Those verbs are passive in which the subject is acted upon. These varieties, it will be noticed, are varieties in both form and meaning, Thus Avw, the active, differs in form from Avopai the middle. It differs also in signification; for while Avw signifies I loose, transitive or intransitive in import; thus, we may say Ave, I loose, using the verb generally without any specific object; here the verb is intransitive; the intransitive form is seen better in Oaλλw, I blossom. We may also say Avw Tov aveρwnov, I loose the man, when Aww has a definite object, and is transitive. Under the head of carbon, we shall have to take up carbonic acid systematically; at this time I merely treat of it collaterally. Examination of the Results of the Combustion of Sulphur in Oxygen. Here again we do not observe any solid result. If the combustion had been conducted in a perfectly dry vessel, or even in a vessel containing water, provided the results of com-Avoμa signifies I loose myself. This active voice may be bustion were examined speedily after the occurrence of that phenomenon, we should have demonstrated the existence of a peculiar gas. In the present instance the gas may be absent inasmuch as it is readily soluble in water. If present you will smell it, if absent the water will be found to contain it; at any rate some will be found absorbed by the water, to which therefore we may first apply our tests. It is sour to the taste. Smells like burning brimstone. Reddens litmus paper, then bleaches the paper. It may or may not whiten lime water: dependent on the mutual quantities of the two. You will now do well to prepare another portion of this gas, and transfer it into a bottle over the pneumatic trough; although the gas be absorbable by water, nevertheless by avoiding unnecessary agitation a sufficient amount may be collected. You will find that it neither burns nor supports combustion, It is called sulphurous acid, and under the head of sulphur will come before us in further detail. Examination of the Results of the Combustion of Phosphorus in Oxygen Gas.-After agitating well the contents of the jar in question, with a little water, you will find that the liquid thus produced is sour, and reddens litmus paper; hence it is an acid. You will also find that the air contained in the bottle is atmospheric air, neither more nor less. Hence the sole result of the combustion of phosphorus is a white solid, exceedingly soluble in water. The solid in question is denominated phosphoric acid, Observe in relation to numbers two and three, as given above, that the English I loose myself, and I am loosed, are very nearly related in meaning. If I loose myself, clearly I am loosed. The chief difference between the two is, that in the former the action is restricted to one person, namely, the subject; while, in the latter, it extends to a second person,the person, that is, by whom the subject is wrought upon. The difference, in consequence, is rather in the person than the act. Accordingly, you see that the form remains the same, being in both cases Avouai. In other words, Avopau may have a reflex (or middle) import, as I loose myself, or a passive import, as I am loosed. Strictly speaking, there is but one form in the present tense. Grammarians differ as to the name which they give to that form, some calling it a middle, others a passive voice. Very few, if any verbs, are known to possess all the tenses of the three voices, as they might be formed analogically. What forms really exist will appear as we proceed. TENSES. Again, study the following forms, which, for the sake of brevity, I at once present arranged, and to which I append | so called because it merely indicates or declares the act; this the meanings: A. Principal tenses, that is 1. Present Ava, I loose. 2. Future Avow, I shall loose. 3. Perfect Xeλvкa, I have loosed. B. Historical tenses, that is 1. Imperfect λvov, I was loosing, I loosed. 2. Aorist ελυσα, I loosed. 3. Pluperfect λελvкeiν, I had loosed. Each of the historical tenses is formed from its corresponding principal, thus Principal Tenses. {Historical The exact manner of their formation will be explained by and by. At present observe that an action may be considered as now proceeding, hence the present tense; as proceeding in past time, hence the imperfect tense; as proceeding in time to come, hence the future tense; as actually done in past time, hence the aorist tense; as having proceeded in past time, hence the perfect tense; and as having proceeded previously to some other past act, hence the pluperfect tense. Accordingly the present tense properly signifies, as in Auw, I am loosening, and the passive, Avoμai, I am being loosened. Mark, also, that the imperfect denotes both an act going on in the past, and a continual and repeated act. The aorist, as the word signifies, denotes an action as simply past, without any exact limitation; and so is called the indefinite (such is the meaning of the term) tense, or the tense of historical narrative. The perfect denotes a past act which, in itself or in its consequences, comes down to or near the present time. The pluperfect denotes an act done and past, when another past act was proceeding, was some Third future passive TETVOμaι, I shall have been struck. forms. verbs, or verbs having a vowel for their characteristic, have only the first form their tenses according to either the first or the sccond forms. The second perfect is sometimes erroneously called a perfect Only few verbs have both the first and the second forms; most Pure verbs middle. completed. or There are Future passive Double forms of the Tenses, as - ετυψα ετετύφειν τέτυφα ετυψάμην ετύφθην A third future, or perfect passive future, is also found, as I shall be struck. MOODS. Mood is a grammatical term employed to 2nd. point out the manner of an action. If I describe an act as simply taking place, I use 1. The Indicative, as Xvw, I loose, is the mood of independence and reality. If I describe an act as dependent on some other act, as dependent on a conjunction or a verb, I employ 2. The Subjunctive, as λvy, he may loosen. This is the mood of dependence, or of conception; so called because it implies dependence on another act expressed or understood; that is, an act really performed or conceived of in the mind. The subjunctive of the historical tenses is, in Greek Grammar, called 3. The Optative, as λvou, I might (or would) loose. If I express an act in the way of command, I use 4. The Imperative, as Ave, loose thou. limited, because they all express the act under certain limitaThese four moods are called finite, that is, definite or tions or modifications. disconnected, that is, with person or number, I then employ But if I express an act indefinitely, or in its abstract form, the mood termed 5. The Infinitive, as Avev, to loose. Another modification of the verb is found in The Verbal Adjective, AUTɛog, he must be loosed, which resembles the Latin participle passive in dus, as amandus, he must be loved; and accordingly has a passive force. THE PARTICIPLE. of the verb and the adjective; as expressive of the quality of Participles are so called because they partake of the qualities the verb they denote action, as expressive of the quality of the adjective they denote modification, e.g. Bovλεvwv avno, a counselling man, that is, a Counsellor. PERSONS. In Greek, as in English, there are three persons; 1st, the speaker, I; 2nd, the person spoken to, thou; 3rd, the person spoken of, he. The persons in Greek are in general indicated by personal-endings, that is, changes in the termination of the verb; as, 1st, person Av-w; 2nd, Av-ag; 3rd, Av-ei. I loose, thou loosest, he looses. In the English termination e, est, es, you have an example of these person-endings. |