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would be abhorred by chemists, and avoided by them to the LESSONS IN CHEMISIRY.-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 of tin for examination. He may employ, to this end, a little 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, wil not serve our purpose. This material is not tin, muriatic acid (spirit of salt), termed by the French acide but iron ciated 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 dissolving gold. As regards The physical aspect of tin is very characteristic, so that, sup tin is not the best for us, the hydrochloric acid
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 fiask, causing the delivery-end of tinguishing them and separating them is by taking advantage tbe 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 flame 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 resultproves that the metaloperated upon is either antimony or tin (p. 156, 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 flint 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 whilst in church, or that iquid in question were generated, a vessel would be required to hold it. I each couple had a separate pew,
Thus is it with many disputed chemical combinations, we
BICHLORIDE OF MERCURY,
Antidote, white of egg. therefore it must be a chloride of sodium; it cannot be hydrochlorate of soda, inasmuch as hydrochloric acid contains hydrogen, and soda contains oxygen, in common salt both do not throw it away. Should you by some mishap swallow
The solution will frequently be required as a test, tierefore these elements are wanting. Dissolve this salt in water, and this amount of bichloride, you would die after the lapse of the 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 or thus :
remember, as a collateral fact, that white of egg is also an
antidote for verdigris and preparations of copper generally. Chloride 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.
rate of Apparently we have not very far advanced with our consiOxygen. 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 10 with the true philosophy of chemistry, which prompts to the one of those truths already mentioned in the course of these
lessons, and which will enable you, if you have been attentive,
CHLORIDE OF GOLD
and preserye 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-marrow, 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 con. same thing, on soda. The term haloid is derived from the traction for hydrargyrus (Lat. for mercury), and CI. for combination of two Greek words, ads, 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 equiva.. Returning 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
As concerns the chloride of gold, you will observe it is its properties. For the purpose of testing, the following reagents 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 or (2.) Of potash (liquor potassæ).
steam bath, the result would be a chloride made up of three (3.) 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. compound
is called in exact chemical language a terchloride, and (5.) Of þichloride of mercury (corrosive sublimate).
thus represented in chemical symbols :
Au., I need scarcely mention is the contraction for the Latin (8.) Hydrosulphate of ammonia.
word Aurum, gold. (9.) Some calomel.
And now for two final experiments.: test the solution just Two of these solutions, of bichloride of mercury and chloride made (protochloride) with hydrosulphuric acid, or hydrosul
, of gold, require each special comment.
phate of ammonia, and remark, the colour is black. Next
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 convents the protochloride into a perchlaride. All ride should be broken into fragments, projected into a Fiorenee the other tests mentioned in order 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 af mereuxy, with pratachlopide of the bottle thus :