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Nitrate potassa.---------------------- KO, NOs
Acetate potassa.--------------. . . . . . . . KO, (CH3)O3
Sulphate potassa.--------------------- KO, SO3
Bi-sulphate potassa................... KO, SO3 + HO, SOs
Sulphate potassa and zinc.............. KO, SO3 + ZnO, SOs

Upon this principle, and notwithstanding the fact that for a long time the organic radicals were entirely hypothetical, the development of organic radicals went pari passu with the study of organic compounds. The following illustration shows how the organic acids were subjected to the radical theory.

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The theory is so simple, so well known, so satisfactory in the explanation of the phenomena to which it is applicable, that the reluctance to abandon it, especially by chemists educated under its influence, is natural. That it has been attacked vigorously, and almost to its fall, is owing to the present great wealth of chemical compounds, and the discovery of phenomena which cannot readily, if at all, be brought in subjection to it. Daily the realm of chemistry is extending, and the boundary line between organic and inorganic compounds is becoming more and more indistinct. If to the atoms of carbon, hydrogen, oxygen, and nitrogen has been assigned a greater facility of mutual chemical attraction, the reason lies less, perhaps, in a peculiarity of the nature of these atoms, than in the kind of experiments to which they have been subjected. Continually, elements formerly called inorganic are added to organic compounds, and it is not too much to expect that the same chemical attractions exist between all of the elements as between C, H, O, and N inter illis. If the right of combining, in indefinite number of atoms, the original organic elements, gives rise to so many “changes,” i.e., compounds, what would it be if each of the sixty-four elements could play an equal part with these? The number of possible chemical compounds would approach infinity, and could only be conceived by the aid of comparison. It would be no exaggeration to compare their number with the distance from the earth of the fixed stars expressed in feet, or even with the diameter of that great orbit in which our solar system is supposed to be moving. It is true that theories are not formed to meet future wants; but, nevertheless, a general consideration that the radical theory was becoming daily insufficient for the rapid increase of chemical facts, urged thoughtful men to invent a theory which should, at least, generalize chemical compounds, and bring them into the proper order and connexion to render their more perfect study possible. A satisfactory theory has not yet been invented, and chemists are loath to abandon totally the electro-radical theory for that of types pure and simple. While the radical theory was in a very flourishing condition, certain newly observed phenomena demonstrated that we could substitute electro-negative chlorine for electro-positive hydrogen in a compound without changing the chemical character of the body to a great extent. Thus, by the action of chlorine (Cl) upon olefiant gas, (C, H,) four Dutch chemists had many years ago discovered a o compound, which has received the name of Dutch liquid, and which has the composition C, H, Cla. When upon this body the action of chlorine was continued, supported by sun light, it was discovered that a series of liquids could be obtained having the same character as Dutch liquid, but differing in that the hydrogen was replaced atom by atom by chlorine, thus:

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4th " CCl6 = (C4C14)Cl2 If upon the members of this series an alcoholic solution of potassa act, one equivalent each of hydrogen and chlorine is separated, and we obtain the following compounds :

From Dutch liquid C.H.Cl, we obtain Camp

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“ 1st substitution C.H3C13 " c.c.}
“ 2d " C.HCl "

“ 3d “ CHCl " CC.; which demonstrates that in Dutch liquid and its chlorine compounds the latter element exists in two conditions : one in which it takes the place of hydrogen, atom by atom, and another in which it unites with carbon and the compound atom thus formed. In other words, the negative atom of chlorine drives out and takes the place of the positive atom of hydrogen. To bring these phenomena in accord with the former electro-chemical theory, we would have to assign to the atom of chlorine a preponderating positive and a negative character at the same time, which was deemed inadmissible.

The same difficulty occurred with respect to the negative atom oxygen, to which, according to some, a place had to be assigned sometimes inside of the positive radical.

The behavior of acetic acid with chlorine gas in sun-light affords a striking example of the substitution of Cl for H. By this reaction, from C, H, 04 (acetic acid) there arises, by the substitution of chlorine for hydrogen, chloracetic acid, (C. 30.) and between the two acids there is a great chemical similarity. They each saturate the same amount of base, and when acted upon by the same reagents, give rise to analogous products. Thus, by heating with excess of alkali, acetic acid becomes carbonic acid (2002) and light carburetted hydrogen, (C, H4) while by the same treatment chloracetic acid becomes

( H ) 2 C 0, and C2 CL or chloroform, which may be regarded as light carburetted hydrogen, in which a portion of the hydrogen is replaced by chlorine. By the action of nascent hydrogen, chloracetic acid is regenerated to acetic acid. It is true that these difficulties might be reconciled by the assumption of both a negative and positive character being assumed under different circumstances by the same atom. This must be done in certain instances to bring the modern type theory in accord with the electro-chemical theory, and, indeed, the experiments of Schoenbein upon ozone, and the phenomena of the action of certain bodies in the “nascent" state, would render this assumption not unlikely; but the immediate result of the experiments cited was to hold the electro-chemical theory in abeyance, and to develop the theory of types.

The first type theory was a theory of the classification of chemical compounds, and was analogous to the natural history system of classification into orders, genera, and species. There was a “molecular” or “mechanical" type which corresponded to the “order;” a “chemical” type to the “genus;” and the various members under the same chemical type corresponded to the “species.” Compounds of the same molecular type consisted of the same number of atoms; but not in binary groups, as the electro-chemical theory required. Under each molecular type were the chemical types, consisting of the same number of atoms (as before) but similarly arranged. The individuals of the same chemical type consisted of the same number of atoms, similarly arranged, but differing in the kind of atoms. The following example will illustrate the

theory: Molecul, Ar TYPE OF TWELVE ATOMS. - Acetic acid..... C, H, O, Individuals of 1st chemical 1st chemical type { Chloracetic acid. C. Cla HO, } type. - Alcohol . . . . . . . C. He O2 Individuals of 2d chemical 2d chemical type { Mercaptan. ---. C. #. S2 } type.

These all belong to the same molecular type of twelve atoms. The first two and the last two belong, respectively, to the same chemical type; the atoms are regarded as being similarly arranged, because acetic and chloracetic acids, on the one side, and alcohol and mercaptan on the other, bear a great analogy to each other in their compounds and in the products of their decomposition by the same reagents. The following method was adopted for writing the formulae according to this theory:

Acetic acid --------------- C, # } O,
Chloracetic acid. . . . . . . . . . . C, o } O,
Acetate of potassa......... C. { } O,
Acetic ether -------------. C. o } O4
Chloracetic ether . . . . . . . . . C. &#, } O,
The following contain C, H, O, but the atoms are arranged differently
Butyric acid.............. Ca # } O,
Acetic ether -------------- C. o }o,
Propionate of methyle....... Co ch, } O,

It will be observed that chlorine, in the type, takes the place of the upper hydrogen atoms and potassium, and the radicals the place of the lower ones, thus indicating the different nature of the several hydrogen atoms in the type; and, further, that this theory was obliged to assent to the idea of “radicals,” namely, groups of atoms playing the part of single atoms.

The type theory met with many supporters, some of them the best thinkers which have enriched modern chemistry; it met with many variations, some of which penetrated far into the realms of fancy; but it would probably have fallen into disuse had not the discovery of the compound ammonias directed the attention of the chemical world to this method of imagining the constitution of chemical compounds.

At the same time that attention to this subject was arrested, homologous series were discovered, (by a type theorist,) and important laws with . to them, such as the relative boiling points of their members, their vapor density, atomic volume, &c., became known; out of which accessions to our knowledge was developed the modern type theory. The compound ammonias are bases bearing a very great analogy to ammonia, their salts being strictly analogous. By the former radical theory it would be impossible to assign to them satisfactory formulae; but by the assumption that they are constituted after the pattern or type of ammonia, their formulae become very simple. They are ammonias, in which one or more atoms of hydrogen are replaced by one or more radicals, thus:

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The laws alluded to above which enable a more correct conception of the chemical constitution of bodies are as follows:

1. The law of even atoms.-The remarkable fact has been discovered that (the eqivalents of O and H being 8 and 1) by far the greatest number of organic compounds contain an eren number of carbon atoms; further, that the sum of the atoms of hydrogen, chlorine, iodine, bromine, nitrous oxide, (N 0,,) nitrogen, and metal is an even number; which is also true for the sum of their oxygen and sulphur-atoms. For example, in Benzoic acid C1. He O, the number of carbon atoms is an even number, and so is that of the hydrogen and of the oxygen atoms.

2. The law of atomic volume—The greater portion of organic compounds experience in the vaporous condition a condensation during the combination of their elements to four volumes—in other words, in the state of vapor their atom occupies four times the volume of an oxygen atom. This law, it will be remembered, is seen by comparing the quotients arising from a division of the equivalents of compounds by the specific gravity of their vapors, and gives the result that the atomic volume of the atoms of the elements and their compounds bear a simple relation to each other, as may be seen from the following table, which is quoted from its bearing upon the type theory:

Names of bodies. Symbol. Division of the Relative atomic! Atomic volume, equiv. by the volume. Oxygen = 1. sp. gr. of vapor. Sulphur---------------------- S.----------- offs 2.41 # Oxygen---------------------- O----------- Târg 7. 22 I Phosphorus------------------ P----------- złłł 7.22 2 §ydrogen.------------------- H----------- wooga 14. 44 2 Nitrogen --------------------- N----------- #; 14. 44 2 Chlorine --------------------- Cl----------- * 14.44 2 Promine---------------------- Br---------- or 14.44 2 "dine----------------------- I.----------- ##! 14.44 2 Water------------------------ HO .... .. g3. 14. 44 2 Sulphuretted hydrogen..... ----|HS.----..... #: 14.44 2 Carbonic acid.......---------. CO:-------- Tołł 14.44 2 Protoxide of nitrogen NO T}#1 14.44 2 12eutoxide of nitrogen roorg 28.88 4 Hydrochloric acid......... †. 28. 88 4 Ammonia -------------------- .# g 28. 88 4 Chloride of ethyle. ------------ #, 28.88 4 Acetic acid ------------------- #. 28. 4 Valerianate of ethyle *}r 28.88 4

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So closely do chemical compounds conform to this law that it is used daily to control vapor density determinations; the experiments show whether the condensation is to 1, 2, or 4 volumes, and whether, accordingly, the equivalent of the body is to be divided by 7.22, 14.44, or 28.88, to calculate the density of its vapor. The calculation is more accurate than the actual experiment on account of the superior accuracy by which the equivalents have been determined. The law of even atoms, and the observation that in most organic compounds the condensation is to 4 volumes, serve often to determine the formulae of organic compounds. Thus, to acetone was formerly assigned the formula Ca H3 O, which satisfies neither law; by doubling its formula (and there is no chemical reason to the contrary) it becomes C6H6O2, which satisfies both laws. For the same reason the formula of ether (C, H5O) may be doubled to Ce H10O2. Again : it has been doubted from its origin and chemical behavior whether amyle obtained from amylic alcohol (Clo His O.) should have the formula Cie Hu, or Cao Hoz; but the latter formula agrees with the law of even atoms, and with a condensation to four volumes. 3. The law of homologous series.—Another law influencing strongly the determination of chemical formulae, and which is one of the most remarkable among the discoveries of modern chemistry, is that of homologous series. The following is an example:

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| Bodics. Formulae, Boiling point. Sp. gr. at Sp. gr. of 00 C. vapor. C, H, Ethyle butyle----------------- Cs H, S = Cia His--- 62o C. 0.701 2.97 Ethyle amyle.---------------- 3, #, ;-co H. . 850 0.707 3.46 Butyle.----------------------- §: # =c, H.... 108° 0.716 3.94 Butyle amyle----------------- 3, #,8–c. o 1322 0.725 4.42 Amyle ----------------------- §:#;}=co. He - e. 0.741 4.91

The members of this series are subject to the “same law;” they advance from the lowest by an increment of C, H2. A general formula for the series would be Cn H(n + 2.) n being an even whole number. Their boiling points as well as their specific gravities in the liquid and in the vaporous condition rise gradually. We have, from its position in this series, an additional reason why amyle should have the formula C20 Hz, and not Clo Hil. Indeed, as may be seen in the table, amyle is regarded as having (in combination) Cin Hu, but, when in the free state, two of its atoms are joined together to form a compound atom Cao Hon. The following are additional illustrations of homology:

I. HYDRocarbons. i II. Acids.

(Cn Hn.) Cn Hn O. I2thylene ----------------- C, H, Formic ..... - - - - - - - - - ... C, H, O, Propylene. . . . . . . . . . . . . . . . Co. He Acetic......... - - - - - - - - C, H, O, Butylene ----------------- Ca Hg | Propionic .............. Cs H, O, Amylene . . . . . . . . . . . . . . . . C10H10 | Butyric........... . . . . . Co Hs 0, Olečne . . . . . . . ------------ C12H12 Valerianic..... --------- Cin Hio O. Paimitic............... c.ii.o.

Stearic ---------------- Cas Has O,

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