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would be abhorred by chemists, and avoided by them to the LESSONS IN CHEMISTRY.-No. XIII.

utmost of their power. The presence of such a liquid would The metal which I purpose making the subject of this day's of different bodies by taking advantage of their several powers of

destroy all our means of analysis. We now effect the separation lesson is tin ; a very interesting, and at the same time a very solubility and insolubility, as you have seen in many cases and useful metal. No student, however remote he may be from will frequently see hereafter. If all the substances which have towns, will experience any difficulty in obtaining a specimen

come under our notice had been equally soluble in either of the of tin for examination. He may employ, to this end, a little fuids employed, there would have been an end to our powers tin-foil, or one of the capsules where with bottles of spirit, of analysis. pickles, &c. are now so frequently occluded. I need scarcely remark that the metallic sheet known as tinplate, and used by To resume the special consideration of tin--hydrochloric or tinmen, will not serve' our purpose. This material is not tin, muriatic acid. (spirit of salt), termed by the French acide but iron coated with tin; however, supposing neither tin-foil chlorhydrique, is a very good solvent for the metal; still better nor a tin capsule to be procurable, which is hardly likely, the is a mixture of hydrochloric with nitric acid, sometimes called student may scrape off the superficial tin coating from a piece nitro-muriatic or nitro-hydrochloric acid, also known as aquaof tinplate.

regia, on account of its property of dissolying gold. As regards The physical aspect of tin is very characteristic, so that, sup: tin is not the best for us, the hydrochloric acid

alone unmixed

our present purposes, however, the generally best solvent for posing this metal to be presented to you in the metallic state, with nitric is what we will employ. you could scarcely confound it with any other. In the first place, it is a white metal; not blue-white, like zinc, but having There are certain reasons, I will not stop to explain them more the appearance of silver. With lead it could not be con- just now, which involve the necessity of our performing this founded, on account of the bright aspect which it always pre-solution in a vessel of such construction that the minimum of serves, whereas lead becomes tarnished. Tin melts with ex- atmospheric air may come into contact with the materials. It treme facility, much more readily than lead ; if held in the follows, therefore, that we ought not to effect the process of flame of a candle, it does not burn, as zinc does ; neither does solution in an open vessel. A flask, therefore, is the proper it oxidize, as is the case with lead similarly treated. In short, apparatus to be employed; and inasmuch as one product of I repeat, tin in a metallic state can scarcely be confounded with the solution will be a gas, the nature of which I should like any other metal ; but you are aware that metals seldom exist you to investigate, let us adapt a perforated cork and a bent in nature in the pure metallic state, hence the only way of dis- glass tube to the solution flask, causing the delivery-end of tinguishing them and separating them is by taking advantage the tube to terminate just under the mouth of a jar or bottle, of their chemical properties. Under the head of antimony I resting, as formerly described, on the shelf of a pneumatic' mentioned indirectly a leading characteristic of the chemical trough. demeanour of tin. I mentioned that this metal, like antimony,

For the performance of this experiment, a Florence flask will is violently attacked by nitric acid (aquafortis), a white inso- answer perfectly well, and a spirit-lamp fame may be employed luble powder remaining.

to aid the decomposition. Care also should be taken that Let us try the experiment. Having placed a little tin-tin- more tin is placed in the flask than there is acid to dissolve ; foil by preference—in a watch-glass, saucer, or something of otherwise we shall not get exactly the kind of solution we that kind, pour upon it a little nitric acid. Chemical action of require. a violent kind immediately ensues. The orange-coloured gas previously observed is again evolved, and oxide of tin remains. This result proves that the metal operated upon is either antimony or tin (p. 186, col. ii), and characteristics by which the chemist readily determines as between these two metals will soon be made apparent.

It may here be remarked, that very strong nitric acid does not readily act upon tin ; if therefore the result as described does not immediately ensue, add to the nitric acid a few drops of water ; you will then succeed.

From a consideration of the properties of tin just mentioned, its conversion into peroxide of tin by the action of nitric acid, it should follow theoretically that the peculiarity might be taken advantage of in analysis. This is indeed the case ; the separation of tin from all metals, save antimony, by converting it into this insoluble powder (peroxide of tin) is an operation of frequent occurrence in analysis.

We will now take cognisance of the peroxide of tin under another phase. We will begin by dissolving the tin in a suit- teral product, the nature of which I shall not stop to explain,

As concerns the gas developed and collected, it is a colla able menstruum, and we will convert the tin, thus dissolved, fully anticipating that the student will accomplish this by his into an insoluble form. By this time you are aware, I assume, own unaided efforts. that chemists usually begin their analytical operations by con- ceased, label the flask proto-chloride of tin, and set it aside.

When the operation of solution has verting into a solution the compound under analysis. There Some chemists term it the proto-muriate or proto-hydrochlorate are exceptions to this proceeding, but I give you the rule. If of tin, by which name therefore the student will sometimes a piece of glass were given you for analysis, you would begin find it denominated in books. Whether it be a proto-chloride by dissolving it; if a piece of compound metal, you would or a proto-muriate, depends on the solution of a problem, and again dissolve it ; if a Aint stone, you would still proceed ac- involves a very curious theory, concerning which chemists have cording to the same rule, you would dissolve it. There is a argued a great deal to very little purpose. solvent for everything, even the hardest, the most intractable bodies; and a knowledge of the proper solvent for any given What ! the student will perhaps exclaim, does the boasted substance constitutes one of the most important parts of a accuracy of chemistry come to this ? Can you not determine - chemical education. I cannot refrain, whilst treating of solvents, the constituents of the solution of tin in spirit of salt? Form

to direct your attention to one of the problems of the alche no hasty conclusion of the sort; we can tell accurately enough mists. These enthusiasts laboured hard to discover one uni- what constituents are there, but we cannot tell how these versal solvent; in other words, a fluid that should be capable constituents are united amongst each other. Take an illustraof dissolving everything wherewith it might come into con- tive case: a certain number of gentlemen and ladies go into a tact. If such a liquid as this should be hereafter discovered, it church arm-in-arm; arm-in-arm they come out of church; but

it does not therefore follow as a consequence of the evidence They forgot, by the way, the important fact, that, supposing the before you, that they sat arm-in-arm wliilst in church, or that iquid in question were generated, a vessel would be required to hold it. I each couple had a separate pew.

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Thus is it with many disputed chemical combinations, we

POISON! pot certain bodies together and they are lost to our view. Afterwards we get them out again, but the manner in which

BICHLORIDE OF MERCURY, they arranged themselves whilst there, is a mystery to us. The solution of common salt in water, affords a very prominent example of one of these disputed facts. Common salt, if dried

Hg. Cla und separated into its elernents, yields chlorine and sodium;

Antidote, white of egg. therefore it must be a chlor-ide of sodium; it cannot be hydrochlorate of soda, inasmuch as hydrochloric acid contains

The solution will frequently be required as a test, therefore hydrogen, and soda contains oxygen, in common salt both do not throw it away. Should you by bonie mishap swallow these elements are wanting. Dissolve this salt in water, and this amount of bichloride, you would die after the lapse of tale mystery begins. It may dissolve as thus :

about an hour. If some ignorant person should apply the

stomach-pump, the time would be less. If, however, imme. Chloride

diately on discovering your mistake, you were to swallow the Sodium Chloride of sodium with water.

whites of five or six eggs, you would live out the full number Water

of your days, none the worse for the dose. Probably you will

consider this fact worth remembering. You may furthermore t us :

remember, as a collateral fact, that white of egg is also an

antidote for verdigris and preparations of copper generally. Cloride Chlorine

That moreover it is a material perfectly harmless in all cases; of

consequently, even though the kind of poison should not be Sodium Sodium

known, you may always give white of eggs. Hydrogen- Hydrochloric HydrochloWater

acid

rate of Apparently we have not very far advanced with our consiOxygen Soda

Soda

deration of the metal-tin. Two points, however, in connec

tion with it we have well determined. It is converted into an Whenever you meet with an ambiguous case of this kind, insoluble white powder by the action of nitric acid, and it remember well the fact that the accuracy

of chemistry is not is dissolved by the operation of hydrochloric acid, yielding as a impugned thereby, Do not waste your time in mere ingenious collateral result a gas, the name of which I have not mentioned, arguments pro and con. People who do this are not imbued but which I expect you to determine. The problem related to

of these with the true philosophy of chemistry, which prompts to the one of those truths already mentioned in the cour establishing of large physical generalisations rather than a lessons, and which will enable you, if you have been attentive, contemplation of these nicely balanced disputes. Some people to solve it. I shall conclude this lesson by informing you, that are such creatures of mere detail that they cannot take a com chloride of gold is made by mixing together

two parts of nitric prehensive view of any thing. Give them a poem to read, acid with one of hydrochloric (by measure), and adding to this their first impulse is to hunt after stray commas, or determine Auid as much leaf gold as it will dissolve." Label the solution disputes of precedence between colons and semicolons. Give

CHLORIDE OF GOLD them chemistry to study, they are delighted with no part of it so much as the endless discussion about the aqueous decomposition or non decomposition of haloid salts, for thus chlorides,

Au. Cl. iodides, bromides and fluorides are termed.

All salts are termed haloid that result from the action of an and preserve it as a test. Touch your skin with a little of this acid containing hydrogen on any body. Thus chloride of tin solution and

observe the colour of the stain-developed by is a haloid salt, inasmuch as it results from the action of to-morrow, remember this result is indicative of gold. hydrochloric acid on tin : in like manner, common salt (chlo- And now one final word relative to the stain of chemical ride of sodium) is a haloid salt, seeing that it results from the symbols referred to in this lesson. Bichloride of mercury has action of hydrochloric acid on sodium, or what amounts to the been represented in the symbol Hg. Cl.. Now Hg. is the consame thing, on soda. The term haloid is derived from the traction for hydrargyrus (Lat. for mercury), and cl. for combination of two Greek words, års, salt, and Eidos, likeness Chlorine, the figure , expresses the fact that one equivalent of or similarity.

mercury or (200 parts by weight) combined with two equiva

lents of chlorine, or 36 parts by weight, gives rise to one equivaReturning now to the consideration of our solution of proto- lent of the bichloride of mercury. chloride or protomuriate of tin (which you please), let us test its properties. For the purpose of testing, the following re

As concerns the chloride of gold, you will observe it is agents will be necessary

simply termed chloride, without any numeral affix, because our

auriferous liquid is a mixture of two distinct chlorides of gold (1.) A solution of carbonate of soda (washing soda). (protochloride and bichloride) in variable proportions. If the

solution were carefully evaporated by means of a water of (2) Of potash (liquor potassæ).

steam bath, the result would be a chloride made up of three (8. Of ammonia (hartshorn).

equivalents, 108 parts by weight, or of chlorium combined with (4. Of carbonate of ammonia (smelling salts).

one equivalent, or 200 parts by weight, of gold. This com

pound is called in exact chemical language a terchloride, and (6.) Of bichloride of mercury (corrosive sublimate). thus represented in chemical symbols : (6.) Of chloride of gold.

Au. Clg (7.) Solution of hydrosulphuric acid in water. (8.) Hydrosulphate of ammonia.

Au., I need scarcely mention is the contraction for the Latin

word Aurum, gold. (9.) Some calomel.

And now for two final experiments : test the solutior: just T wo of these solutions, of bichloride of mercury and chloride phate of ammonia, and remark, the colour is black! Next

made (protochloride) with hydrosulphuric acid, or hydrosul. of old, require each special comment,

boil the protochloride with nitric acid, and then test it. The The former may be made of almost the strength of ten colour will be a sort of yellow, because the act of boiling with grains to two wine-glasses full of distilled water. The bichlo- nitric acid converts the protochloride into a perchloride. All ride should be broken into fragments, projected into a Florence the other tests mentioned in our list affect solutions of tin. flask and boiled with the water. When cold, pour the solu. Let the student observe their re-action., more especially the tion into a bottle glass stoppered by preference) and label effect of mixing bichloride of mercury with protochloride of the bottle thus i

tin,

1

ON L'HYSICS OR NATURAL PHILOSOPHY.

where the one represents the effect of a tube immersed in

water, and the other that of a tube immersed in mercury. No. XIV.

Fig. C.

Fig. D. CAPILLARY ATTRACTION. Capillary Phenomena.-In the contact of solids and liquids, a series of phenomena are produced, to which the name of capillary phenomena is given, because that they are particularly observed in tubes, whose diameter is so small that it is comparable to the thickness of a hair.

The effects of capillary attraction are very various; but in all cases, they are the result of the mutual attraction of the liquid particles to each other, and to that attraction which subsists between these particles and solid bodies. Take, for example, the following phenomena : when we immerse a solid rod in a liquid which will wet it, the liquid, in opposition to

Mercury. the laws of hydrostatics, rises around the solid rod, as in the case of glass and water; and its surface, instead of being hori.

When the liquid is contained in a vessel so large as that zontal, takes a concave form, as shown in fig. 47; but, if a solid capillary attraction has no longer an effect on its level surface, rod be immersed in a liquid which will not wet it, as in the still the liquid rises or sinks on the sides of the vessel, accordcase of and mercury, the liquid, instead of rising, sinks ing as it wets or does not wet these sides, see figures and F. round the solid rod, and its surface takes a convex form, as

Fig. E.

Fig. F. shown in fig. 48.

Fig. 48. Fig. 47.

Water.

Laws of Ascent and Depression in Capillary Tubes.-M. GayLussac has proved by experiment that the ascent and depres

sion of liquids in capillary tubes, are regulated according to These phenomena become more evident, when, instead of a the three following laws : 1st. There is an ascent when the solid rod, we immerse in the liquid glass tubes of small dia- liquid wets the tubes, and a depression when it does not wet meter, as shown in the following figures a apd B. According them : 2nd, this ascent and depression are in the inverse ratio

of the diameters of the tubes, so long as they do not exceed Fig. A. Fig. B.

the tenth part of an inch : 3rd, the ascent and depression vary with the nature of the liquid and with the temperature; but they are independent of the substance of the tubes and of the thickness of their sides, if the latter be previously wetted. These laws hold good in a vacuum as well as in air.

The method employed by M. Gay-Lussac in the discovery of these laws was the following: 1st, he measured the interior

Fig. G.

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the surface of the liquid takes the form of a concave meniscus (Greek crescent-shaped), as in fig. 49, and when the tubes are not wetted by the liquid, the surface takes that of a convex meniscus, as in fig. 50. The surface of the liquid assumes the diameter of the tubes, not directly, which would have been same concavity and convexity on the sides of the vessel which very difficult, but by selecting those which presented the same contains the liquid according as it wets or does not wet the sectional area throughout their whole length, and weighing the sides of that vessel, as shown in the following figures o and D, I quantity of mercury which completely filled them; the density of the metal being known, it was then easy to deduce, from its other so as to form an angle, and be immersed in a liquid weight and the lieight of the column, the required diameter, which wets them, so that their line of contact be placed verti. as shown in a former lesson : 2nd, he then placed the liquid cally, the liquid wiil rise towards the vertex of the angle under consideration in a vessel a BCD, figure o, and vertically between the two plates, and its surface, from the highest to the immersed in it, the capillary tubes which were successively lowest point, will assume the form of the curve called an submitted to experiment; close by each tube, he placed a rod equilateral hyperbola. The asymptotés of this curve which is RF, tapering to a point, which, by the motion of a screw, was double, being traced on each plate, are the vertical straight made to reach the exact level of the liquid; then, by means of line in which the edges of the plates meet, which is common a cathetometer, he measured the vertical distance between the to both, and the horizontal straight lines which determine the upper extremity of the column of liquid in the tube, and the level of the liquid in which they are immersed, as shown by lower extremity or point of the rod which came in contact the dotted lines in the following figưre n. with the liquid. The heights which different liquids reach are by no means the same, as may be seen in the following

Fig. H.
table; for, in a tube whose interior diameter was about one
twenty-fifth part of an inch, the liquids rose to the different
heights here mentioned, above the level of the liquid in the
vessel :
Liquids.

Heights.
Water

1.173 inch
Alcohol

0:479 Spirit of Turpentine 0:501 In the experiments of which these are the results, the liquids were kept at the same temperature ; for in proportion as he temperature rises, the capillary phenomena are rapidly minished.

in the use of several apparatus, it is necessary to know the mnount of the depression of the mercury in glass tubes. The following table gives these depressions to the nearest thousandth of an inch, in tubes varying from 8 hundredths to 40 hundredths of an inch in diameter.

When the line of contact of the two plates is horizontal

instead of vertical, as shown in their sections represented in Diameters of Tubes.

Depressions of Mercury. figs. 52 and 53, and the plates are placed so as to form a very •08 inch

.178 inch

small angle, a drop of water put between them is hollowed at •10

•143

both its extremities into a concave meniscus, as in fig. 52, anà •12

•117
•14
•098

Fig. 52.
•16

083 .18

071 •20

*061 .22

•053 .24

•047 .26

•041 .28

•036 •30

*032
•32

028
•025

Fig. 53.
•36

·022 .38

020 .40

018 Laws of Ascent and Depression between two Plates Parallel or Inclined.-Phenomena analogous to those presented by capillary tubes, are produced between two bodies of any form immersed in a liquid, when they are sufficiently near to one another.

Mercury. For example, if we immerse in water two parallel plates of zlass so near each other that the two curvatures formed at their contact with the liquid, are united, it is observed : 1st, is attracted towards the vertex of the angle of the two that the water rises regularly between the two plates, in the plates; but if the liquid does not wet the plates as is the inverse ratio of the interval which separates them; and, 2nd, case with mercury, the drop of the liquid is rounded that the height of ascent for a given interval, is the half of that at both its extremities, into a conrex meniscus, as in fig. 63, which would have taken place in a tube whose diameter is and is repelled from the vertex of the angle. The directions of equal to this interval. If parallel plates are immersed in mer attraction and repulsion in these figures are indicated by the cury, depression takes place, but according to the same laws.

arrow heads. Fig. 51,

The force of attraction of a liquid to the sides of a vessel lies between two extreme cases; it is equal to that of the liquid to itself, or it is zero ; in the former case, the ascent of the liquid in tubes is the consequence; in the latter, depression is the result. Between these two extremes, there must be the case in which there is neither ascent nor depression; this occurs when the force of the attraction of the ligaid to the solid is exactly equal to half of the force of the attraction of the liquid to itself. Water brought in contact with well polished steel appears to realise this particular case ; for the liquid seems, on the approach of the metal, to experience neither elevation nor depression.

As already observed, every column of liquid elevated by

capillary action is terminated by a concave surface; and every li two plates of glass, a B and ac, fig. 51, be inclined to each column depressed, by a convex surface. In cylindric tubce of

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