Page:Encyclopædia Britannica, Ninth Edition, v. 18.djvu/255

 P A R P A B 237 the blessed does not necessarily imply so mechanical a con ception as we find in the Jewish apocalypses ; to speak of the future bliss at all, without the use of metaphysics, is possible only in the form of poetical description, and for such description the story of the garden of Eden supplied the necessary concrete elements, which the apocalyptists took literally, while higher thinkers used them as symbols and ordinary language, perhaps, as mere conventional equi valents for ineffable things. Thus the images borrowed from Eden in such a prophecy as Isa. xi. are certainly not meant literally, any more than the figure of the tree of life in the book of Proverbs. So in the New Testament even Rev. ii. 7 is plainly figurative, and in Luke xxiii. 43 paradise is simply the place of bliss. In 2 Cor. xii. 4 paradise is a heavenly place where ineffable words were heard by Paul ; but he himself does not know whether he visited it in the body or out of the body. See Dillmann s Buch Enoch, and his articles &quot; Eden &quot; and Paradies &quot; in Schenkel s Bibel- Lexicon ; Weber, Altsynagogale Thcolocjie ; and the books on Biblical theology. The Mohammedan paradise (al-Janna) is borrowed from the Jews, as appears from the name Jannatu Adnin, that is, Garden of Eden. It is described in the Koran and by later theologians as a place of all sensuous delights, where the righteous recline on couches in a fair garden drinking the delicious beverage supplied by the fountain Tasnim and waited on by damsels with great bright eyes (&quot;Hur,&quot; Kor. Iv. 72, hence our &quot;houri,&quot; which is properly a Persian form). The expression &quot; gardens of Firdaus &quot; (the Persian form of the word Paradise) occurs in Kor. xviii. 107, and is interpreted as meaning the highest region of the Janna (Beidawi in I.) PARADISE, BIRDS OF. See vol. iii. p. 778. PARAFFIN. In the course of his classical investiga tion on the tar produced in the dry distillation of wood, Reichenbach in 1830 discovered in it, amongst many other things, a colourless wax-like solid which he called paraffin (parum affinis) because he found it to be endowed with an extraordinary indifference towards all reagents. A few years later he isolated from the same material a liquid oil chemically similar to paraffin, to which he gave the name of eupion (eiWwv, very fat). For many years both these bodies were known only as chemical curiosities, and even scientific men looked upon them as things entirely sui generis ; this was natural enough as far as paraffin is concerned, but it is rather singular that it took so long before it was realized that eupion or something very much like it forms the body of PETROLEUM (q.v.), which had been known, since the time of Herodotus at least, to well up abundantly from the bowels of the earth in certain places. Though extensively known, it was used only as an external medicinal agent, until the late Mr James Young conceived the idea of industrially working a com paratively scanty oil-spring in Derbyshire, and subse quently found that an oil similar to petroleum is obtained by the dry distillation of cannel coal and similar materials at low temperatures. This discovery developed into a grand industry, which may be said to have led to the utilization of those immense natural stores of petroleum in America. Scientific chemists naturally directed their attention to the products of these new industries, and it was soon ascertained that solid paraffin and eupion, as well as natural and artificial petroleum, are substantially more or less impure mixtures of saturated hydrocarbons ; and so it comes that, on the proposal of H. Watts, the word paraffin in scientific chemistry has been adopted as a generic term for this class of compounds of carbon and hydrogen. When the electric light is generated within an atmo sphere of hydrogen, then, at the immense temperature of the electric arc, part of the carbon of the charcoal terminals unites with the hydrogen into acetylene gas, C. 2 H 2. Apart from this isolated fact, which was discovered by Berthelot in 1862, it might be said that the two elements are not capable of uniting directly, although an innumerable variety of hydrocarbons exist in nature, and can be pro duced artificially from organic substances. Individual hydrocarbons may differ very much in their properties. At ordinary temperature and pressure a few are gases; the majority present themselves as liquids ; not a few are solids. But the solids are fusible ; and all liquid or liquefied hydrocarbons, at a high enough temperature, volatilize, as a rule without decomposition. To the latter circumstance to a great extent we owe our precise know ledge of their chemical constitution. In all the numerous series of hydrocarbons the percentages of carbon vary from 75 (in marsh gas) to 947 (in chrysene). Within this narrow range of some 20 per cent, several dozens of elementary compositions have to be accommodated ; and many of these, to be represented in formulae C X H^ with an adequate degree of precision, require formulas in which the coefficients x and y are so large that, by means of integers less than these, any fancy composition (within our limits) may be expressed with a degree of exactitude which is quite on a par with the analyses. But these hydrocarbons, in general, can be volatilized into gases, and in regard to these Avogadro s law tells us that quantities proportional to the mole cular weights (i.e., the weights represented by the true chemical formulae) occupy the same volume. Hence, to find the true value, M = C;eHj,, of the formula as a whole, we need only determine the vapour density, and from it calculate the weight of the respective hydrocarbon which, as a gas at t and P millimetres pressure, occupies the same volume as, for instance, H 2 parts of steam. This is M. The elementary analysis enables us to calculate the weight x x C of carbon contained in M parts, and the analysis must be very poor to leave us in doubt as to whether it is for instance 6 x 12 parts of carbon or 7x12 parts that we have to deal with. The reader will now understand how it has been possible to ascer tain the elementary composition of all pure hydrocarbons with a degree of precision which goes beyond that of the analysis, and to prove what analysis could never have done by itself, namely, that there are numerous groups of hydrocarbons which have absolutely identical elementary compositions, cases of isomerism, as they are called. We speak of isomerism in the narrower sense &quot; when the atomic formulae are identical (there are, for instance, two hydrides of butyl, C 4 H 10 ), while we speak of &quot;polymeric&quot; bodies when the several formulae are integer multiples of the same primi tive group (e.g., ethylene, 2 x CH 2 , and butylene, 4 x CH 2 , are polymers to one another). The following table gives an idea of the several classes of hydro carbons which for us come more particularly into consideration. n Paraffins. Olefines. Acetylenes. Benzols. I CH 4 Vacat. Vacat. Vacat. 2 C 2 H 6 C 2 H 4 C H, 2 ~s Vacat. 3 C 3 H 8 C 3 H 4 S &quot;M Vacat. 4 C 4 H 10 C 4 H 8 - -R Vacat. 5 C-H 12 -S &quot; Vacat. 6 C 6 H 14 C 6 H 12 C 6 H 6 7 8 C 7 H 16 C 7 H 14 a 3 a &amp;gt;&amp;gt; C 7 H 8 r H as a o n~w&quot; ^9 M 12 n C B H SB+2 C n H 2ra HH s rt i C n H 2n _ 6 The first column, under &quot;n,&quot; gives the number of carbon atoms per molecule in the compounds whose formula} stand in that hori zontal line, these latter being arranged in a descending series according to the number of hydrogen atoms united with n atoms of carbon. Instead of pointing out those regularities, in regard to the atomic proportions in which carbon and hydrogen can unite into compounds, which the table illustrates so forcibly, let us rather state that the &quot;benzols,&quot; in opposition to all that stands to their left in the table, are things of their own kind. In them six atoms of the carbon are most firmly united (into a &quot;ring,&quot; as a certain theory says), and the rest are, so to say, hooked on to the ring in a less intimate fashion. Thus benzol is (C 6 )H 6 ; each one of the six H s being tied to one of the six C s ; toluol is (C B H 5 ) CH 3 ; it is a benzol from which one of the six hydrogen atoms has been removed, and in which the gap left has been filled by a &quot;methyl,&quot; CH 3 : C 6 H 6 + CH 4 = H 2 + (C 6 H 5 )-(CH 3 ). Benzol. Marsh gas. But similarly two dehydrogeuated benzols, C 6 H 5, can unite into one double ring of diphenyl : 2C.H 8 - 2H = (C 6 H 6 )(C 6 H 6 ) ; and two benzol rings may unite more firmly in such a manner that two carbon atoms of the one ring do service for the two rings, and a double ring is formed firmly united by these two common carbons, the four hydrogens of the original two benzols being away. This gives naphthalene : C 6 H 6 + C 6 H G -2C-4H = C 10 H 8. Benzol. Naphthalene.
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