Page:Encyclopædia Britannica, Ninth Edition, v. 18.djvu/257

 PARAFFIN 239 mixture, only chemical methods can help us out of the difficulty. The following table (extracted from Roscoe and Schorlemmer s Handbook of Chemistry, German edition) gives the names, specific gravities, and boiling points of the more important paraffins. The first column, &quot; n, &quot; gives the number of carbon-atoms in the molecule, and consequently the molecular weight M and the vapour density S. In the case of &quot;pentan,&quot; for instance, we have n = 5 ; hence M = C 5 H 12 = 72 ; and, as H 2 = 2, the gas-density, referred to hydrogen = S = 36, while, as air is 14 45 times as heavy as hydrogen, for the gas-density referred to air the value n 1 2 Q 4 .j 5 6 6 i; i; &amp;lt;; 7 7 7 7 s S 8 9 !l 9 10 10 lo 11 12 13 1 1 L6 it; Name. Boiling Point in Degrees. Sp. Gr. of Liq. at&amp;lt; C. Fahr. Cent. t Liquid at 1 pressure (( Liquid at +4 (Cailletet). 13 to 22 +34 + 1 99 to 102 86 49 156 144 140 136 109 to 118 209 s 195 205 187 to 180 258 227 221 to 223 297 to 298 270* 266 331 to 334 320 320 Not 396 532 1 C. and 180 Cailletet). C. under 46 -25to-30 + 1 -17 +37 to 39&quot; 30 9 -5 69 62 60 58 43 to 48 98 -4 90 -3 96 86 to 87 125-5 108-5 105 to 106 147 to 148 132 130 166 to 168 about 160 160 yet isolated. 202 278 atmospl atmospl 0-600 (?) 0-6263 0-6385 (?) 0-663 0-701 (?) 0-6769 (?) 0-7005 0-6969 0-689 0-7111 0-7188 0-7111 (?) 0-7279 0-7247 (?) 0-7394 (?) 0-7413 (?) eres leres (?) iV 14 iV

io &quot;d

27

13-5

13-5 &quot;6

( Isobutan or trimethylmethan, a gas Methyl-diethylmethan Hexmethylethan, fuses at 96 ^ to 97 j&quot; Dimethyl-heptylmethan Tetramethyl-hexan or &quot; diamyl &quot;... &quot;^ &amp;gt; Not isolated yet. Hekdi ka-dekan, normal, fuses at ) + 21 C f Probably all the paraffins enumerated in the table are present in paraffin oil and in petroleum ; those marked * have been actually found in the one or the other. The solid paraffins are not known as unitary chemical substances ; no chemist as yet has succeeded in splitting up solid paraffin into its proximate components. The manufacturer, in regard to the liquid paraffins even, does not trouble him self with the isolation of chemical species ; he contents himself with splitting up his oil into fractions correspond ing to certain ranges of boiling point, and consequently adapted to certain practical applications. But even the boiling point is not much heeded industrially ; the several kinds of oil are defined by their specific gravity at 60 F., which, as experience shows, increases as the boiling point rises. But it is as well here to point out that the same (initial) boiling point even, and in a much higher degree the same specific gravity, may be exhibited by oils of widely different proximate composition. Hence a relatively (and in a sense sufficiently) high specific gravity is no guarantee against dangerous inflammability ; the degree of inflammability in an oil must be and in practice always is being determined by direct experiment. For this purpose it is not sufficient to heat a sample oil in an open vessel gradually to higher and higher temperatures, and to note the temperature at which the atmosphere over the oil proves inflammable when a lighted taper is brought in contact with it. By this method (which formerly was the universally recognized test) the most varying results may be obtained with the same oil. Far more trustworthy is the close test first proposed by Keates about 1870, the principle of which is to heat the oil within a close vessel which is opened only from time to time to apply a light to its atmosphere. For the execution of this test many varieties of apparatus have been proposed. That adopted by Abel, and now (1884) legally recognized in Great Britain, is made of sheet copper, the exact thickness of which is prescribed for every part. The oil is placed in a close cup, suspended in an air-bath, which latter is heated by immersion in a warm- water bath, provided with an air-jacket. The top of the oil cup is pierced with three circular orifices, one in the centre for trying the best flame, and two smaller lateral holes for admitting air at the close of each trial. The holes are covered by a slide so contrived that when the central hole has become almost uncovered the lateral ones are also open. The slide carries a small colza-oil lamp suspended on trunnions, having a flame of a prescribed size. A pendulum two feet in length vibrates in front of the observer, who, in testing, withdraws the slide slowly during three vibrations, tilts the lamp to bring its flame in contact with the atmosphere of the vessel, and quickly shuts the slide during the fourth vibration. To execute a test the oil at about 60 F. is placed in the cup, which is immersed in the water-bath having water of 130 F. A thermometer plunged into the oil and another in the water-bath indicate their temperatures. When the oil has approached its presumable flashing point, trials are made at each rise of 1 F. in the temperature of the oil. The lowest temperature at which the atmosphere of the cup inflames is the flashing point of the oil tested. The legal minimum flashing point of burning oil by the close test is 75 F., corresponding to about 100 a F. by the obsolete open test. The variety of mixed paraffins which the oil-distiller produces may be arranged under the following heads : (1) oils too volatile to be available for domestic illumina tion, serving chiefly as solvents ; (2) burning oils, as required for house lamps ; (3) oils of very high boiling point, available, and used chiefly, for lubricating purposes ; (4) solid paraffin. The products of the second class have long come to practically supersede the colza oil which used to be the illuminating oil par excellence. Over it they offer the advantages of greater cheapness and of giving, weight for weight, more light. But their drawbacks are that, how ever carefully refined they may be, they have, when allowed to leak out, or in lamps of inferior construction, a somewhat disagreeable pungent odour, and that there is always a lurking danger in the possible presence of highly volatile inflammable hydrocarbons. Colza oil will never burn without a wick ; paraffin oil or petroleum may do so. Products of the second and third classes, separately or combinedly, are of course available as fuels proper, i.e., for the production of heat. At the time when mineral oil was first produced in great quantity in America, the advantages it would offer as a fuel for marine boilers especially were very emphatically insisted on. Of course mineral oil can be more economically stored than coal, and its combustion-heat is susceptible of more exhaustive utilization. The latter fact forms the raison d etre of those beautiful petroleum kitchen-stoves and culinary lamps which are very much used on the Continent where gas is not at hand. But to talk of mineral oil as a cheap fuel for wholesale heating is nonsense. H. St Claire Deville, about 1870, made an extensive investigation on the calorific value of American petroleum which, as we know, is pretty much the same thing as paraffin oil. He used a large apparatus, enabling him to burn several hundred litres of oil in one experiment ; in fact he realized