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album; and, secondly, because the watermark and texture of the paper cannot be examined. The best method of mounting stamps is as follows, which is very simple, but rather difficult to describe clearly. Take a slip of thin white paper about half an inch in breadth. Smear it on one side with Indiarubber cement, white starch, dextrine, or thin clear gum. When dry, fold the slip in two lengthways, keeping the gummed side outermost. Next, cut it into pieces rather narrower than the stamps required to be mounted; each of these pieces will then be in shape like a hinge, the two outer sides being gummed. Attach one side, by moistening, to the stamp; and, when this is dry, attach the other side to the album: the stamp can then be moved up and down like the lid of a box. The advantage of this plan is very evident. If it is wished to remove a stamp, the greatest damage that can be done by the most clumsy person is to tear the piece of paper which acts as a hinge; and, of course, another hinge can be easily attached, and no injury is done to the stamp. Then, again, the watermark, texture of paper, and perforation can be examined and referred to at any time: this is especially a great convenience to philatelists of the French school. The hinge should be rather narrower than the width of the stamp, in order that, in the case of perforated labels, the perforations may be clearly seen; and it should also be fixed to the top of the stamp, just below the perforation. A narrower hinge would also do, if rather thicker paper be used.

Since collecting has become so general, and stamps are in such demand, numerous dishonest dealers in postage-stamps defraud to a very great extent inexperienced collectors by selling imitations of rare stamps at very low prices. They insert in boys' magazines and papers some such advertisement as this: "A bargain! A Packet of Thirty very Rare Stamps for Sixpence! including Pony Express, Sandwich Islands 13r., Costa Rica, Due di Parma, Yellow Austrian Mercury, View of Sydney, Old Lubeck, Swiss Zurich, Monte Video, Buenos Ayres, and many others. Only 6d., post-free!" Many a boy has spent his pocket-money on such packets, and finds afterwards, to his dismay, that all these mentioned rarities are worthless forgeries. If a boy wishes to purchase packets of stamps, let him be careful to go to a known and respectable dealer. Collectors must not suppose, because some dealers in their advertisements warrant all their stamps to be genuine, that therefore all their stamps are genuine. Very often these very dealers advertise rare stamps at so low a price, that this very fact is proof that all their stamps are not genuine. It is necessary to be very cautious both in buying and exchanging: examine well and carefully, and, in a case of doubt, consult, if possible, an experienced friend before finally accepting. Very many rare and very many common stamps are forged. An observant collector may often know them by their smudginess, and the inferiority of their execution compared with the originals; but sometimes they cannot be detected without a closer and more critical examination. Forgeries, or, as they are sometimes called, faesimiles, are so plentiful that some have counselled young collectors to aim at obtaining no stamp issued earlier than 1861 ; there are, however, imitations of many stamps emitted since that date, and the only safeguard against being duped is cautiousness and careful study.

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CHEMISTR Y.

Chemistry is the science which teaches us the nature of the component parts or elements of the earth, and especially the relations which these elements bear to each- other.

Formerly it was considered—and the notion is not yet quite exploded—that there were only four elements, viz., earth, air, fire, and water; and these were called elements because it was supposed that they were simple bodies, that is, bodies which could not be produced in their apparent form, except by the hand of Nature. Now, this being the true meaning of the word element, chemistry has discovered that none of these four things are elements; for she has, so to speak, dissected them all, and can not only exhibit in a detached form the true elements of which they are made, but can also unite the true elements in such proportions as to reproduce the substances which ertwhile she split up.

The chemistry which splits up a combination of elements is called analytical chemistry (resolving any substance into first principles); and that which reproduces broken combinations, or builds up others, is called synthetical chemistry (joining elements into a compound). To both of these the student will be introduced.

To account for our forefathers not reckoning the metals amongst elements, it must be borne in mind that they made a distinction between base and noble metals—a sort of House of Commons and House of Lords amongst minerals—and believed that, by a process which they called transmutation, the members of the lower class could be changed into members of the upper class, so that iron might become gold, and lead silver, and so on. Some cunning men, working on the avarice of their fellows, pretended to a knowledge of this process, and to be able, by means of the " philosopher's stone," to enrich without stint the man who would only spend enough money to defray the cost of their operations. The histories of the Middle Ages are full of the records of chemical rogueries of this kind, which would have been impossible if folks fiad only known, as we know now, that all metals are elements, unchanging and unchangeable in their nature, entering into many different forms and combinations, but ever in themselves the same, and utterly incapable of conversion.

An element, therefore, is a body constituted of perfectly identical particles, and incapable, so far as chemistry hitherto knows, of being resolved into components. Of this kind of element chemistry at present numbers the following:

TABLE OF ELEMENTS.

(The names in italics are those of the elements commonly met with.)

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It is quite possible that as chemical knowledge becomes greater, some of these bodies may be struck out of the list, and others yet to be found may be added; but, as far as we know now, the above list contains all the elements.

The letters put against each clement signify the name by which it is known in chemical language, a language highly necessary, as will be shown, and without a knowledge of which the real student of the science cannot advance a step. He may play at chemistry, and, under direction, produce certain effects with the chemicals at his disposal; but he will understand nothing of what he is about, nor will he perceive the " reason why " of the changes wrought before him. He should learn the language of the region in which he is about to travel, or he will meet with nothing but misadventure; and the language is so simple that there is no excuse for his not mastering it thoroughly.

By the use of symbolical letters to represent the words, and by the use of little figures placed to the right of the symbols, the names of the elements in any combination of elements can be seen at a glance, together with the proportion in which the elements are combined. Thus Cu, as will be seen by reference to the table, is the symbol for cuprum or copper, O is the symbol for oxygen, and S is the symbol for sulphur. These three elements combine in certain proportions to make sulphate of copper (blue vitriol); but to write the words "sulphate of copper" conveys no idea of what elements, or how much of them, are contained in this substance. Let us sec how it looks in chemical language: CuO,SO3. Here we see that in order to make up this salt, one part of copper unites itself with one part of oxygen to form what is called the base of the salt, and that one part of sulphur unites with three parts of oxygen to form sulphuric acid, which is the acid of the salt; so that at a glance we see —written in a smaller compass, too, than is the common name of the salt—the exact nature and composition of sulphate of copper.

But this is not the only advantage of symbols. By their aid we are enabled to work out on paper, without seeing the chemicals, the changes which two substances will work in each other when brought intimately together. Indeed, but for them it would often be impossible to trace the operation of causes to their final results. With them, there is no chemical process so delicate or difficult but it may be followed, detective-like, to the end.

The student should not attempt to practise with his chemicals and apparatus till he has well drilled himself in the use of the symbols; and when he sees in practice any fresh combination brought about by the means of any of his processes, he ought invariably to aceount for it on paper, and ascertain, through the symbols, what that new combination is.

Acids not containing oxygen will not unite with bases containing oxygen; so that, whenever there is an oxygen acid, as nitric (NOs) or sulphuric (SO3), oxygen must be derived from somewhere or other among the elements to join with the base before a salt can be formed. The reverse is the case with hydrogen acids, as hydrochloric (HCI) or sulphuretted hydrogen: any oxygen in the base must be got rid of before union can be effected.

In order to understand the operation of the symbols in accounting for chemical changes, it must be borne in mind that even amongst chemicals there are strong likes and dislikes, one element preferring another above its peers so strongly that, when possible, it will always hasten to make a combination with it, even at the cost of a previous combination. Thus, if a solution of sulphate of copper (CuO,SO.,) be introduced to a solution of nitrate of lead (I'bO,NO6), a precipitate of sulphate of lead (PbO,SO,.,) will be thrown down, because the lead, having a stronger liking for the sulphuric than the nitric acid, hastens to form an alliance with it. giving its former uncongenial acid to the copper, with which it unites (still in solution) to form nitrate of copper (CuO,N06).

The law by which these likes and preferences—ascertained in the course of long chemical experiences—are regulated is called the law of chemical affinity, that is, "chemical relationship." A knowledge of it will come gradually. To assist in acquiring the knowledge, let it be remembered what is said above as to the unions of oxygen acids and hydrogen acids with bases to form salts.

The student should practise writing the names of his chemicals in chemical language. Let him also express any chemical he has to mention in the like way. Study the composition of the chemically written names of the reagents on p. 588 with reference to the table of elements already given; and exercise by supposing, on paper, the introduction of the reagents to some previously existing combination of elements, as in the following examples, where the actual changes arc worked out:

Substances added. Substances formed.

HCl (Hydrochloric acid). ( Wv*^ SiK'er)

AgO.M, (Nitrate of silver). \ gg^g."0*

NH^O.SOg (Sulphate of ammonia). BaO,SO:) (Sulphate of baryta). Ba,Cl (Chloride of barium). NH4,Cl (Chloride of ammonium).

HS (Sulphuretted hydrogen). j Jfcf gftgj^ lcad)'

PbO,N05 (Nitrate of lead). j Ho'(Water)

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The Laboratory.

The construction of such a laboratory as will be amply sufficient for the wants of a beginner need not — indeed, should not—be an expensive affair. It will require the exercise of some ingenuity and the proper application of such hints as are here given; but the outlay of money need be only trifling.

First, a bench or table, which may be wholly devoted to the purpose, is to be got. An old bed-room table, the commoner the better, will do admirably;

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