NAPHTHA 387 



hydrocarbons which issue from tho earth in certain parts of the world. In this way 

 mineral burning-oil, when first introduced, was called Boghead or Bathgate naphtha ; 

 but the term was objectionable, as it confounded the safe-burning oil with the explo- 

 sive spirit which also is applied to different technical uses, and it is now completely 

 in abeyance. The light spirit from shales and cannels are identical, being composed 

 partly of the olefianl, partly of the paraffin series, while earth-naphtha appears to 

 belong to the latter series. Coal, caoutchouc, bones, wood, and peat, during destruc- 

 tive distillation, first give off naphthas, which are distinguished by their lighter 

 specific gravity when compared with the later products from the still. But this is 

 comparative ; for, while an ordinary shale-naphtha may have a density of about 

 0-750, coal-naphtha has commercially a specific gravity of 0'850. 



A description of the new methods of refining shale-oils and naphtha is given further 

 on. (See SHALES AND MINERAL OILS.) But the following description by Greville 

 Williams of his early investigations on Boghead-naphtha (as all the light distillates 

 from Torbanehill mineral were at first designated) is classical. 



On the Chemical Nature of the Fluid Hydrocarbons constituting Boghead- 

 Naphtha. 



If, when preparing paraffin-oil from coal, the crude oil is rectified with water, a 

 clear transparent naphtha is obtained. This fluid, as found in commerce, is by no 

 means of constant quality. By quality we mean the power of distilling between given 

 limits of temperature. Some kinds are of about the same degree of volatility as com- 

 mercial benzole, while others distil at nearly the same temperatures as common coal- 

 naphtha. The hydrometer is not a safe guide in choosing this naphtha ; this arises 

 from the fact that photogens, of very different degrees of volatility, have almost the 

 same densities. The safest plan is to put the fluid into a retort, having a thermometer 

 in the tubulature, and distil the contents almost to dry ness. The careful observation 

 of the range of the mercurial column during the operation is the best mode of ascer- 

 taining the quality of the fluid. 



The more volatile portions which distil over with water are free from solid bodies, 

 and consist of a mixture of fluids belonging to three series of homologous hydro- 

 carbons, namely, the benzole series ; the olefiant gas, or OH n series ; and the radicals 

 of the alcohols. 



As no works on chemistry contain any directions for the proximate separation of 

 complex mixtures of hydrocarbons, the following description of the method adopted 

 by the author of this article for the separation of the substances contained in Boghead- 

 naphtha may be useful. 



It is necessary, in the first place, to determine whether each substance is to be 

 obtained in a state of absolute purity, or whether it is merely desired to obtain 

 tho various series distinct from each other. In the process given, it will be supposed 

 that the individual hydrocarbons are required in a state of purity, because it is easy 

 for the operator to leave out any part of the method which may be unnecessary under 

 the particular circumstances of the case. The first step is to obtain constant boiling- 

 points, for it must be remembered that if, when any organic fluid is subjected to 

 distillation with a thermometer in the tubulature of the retort or still, the mercury 

 continues to rise as the fluid comes over, it is at once demonstrated that the substance 

 distilling is not homogeneous. In order to obtain the fluids of constant boiling-point, 

 it is essential to subject them to a complete series of fractional distillations. This is 

 an operation involving great labour, so much so that, in investigating Boghead- 

 naphtha, upwards of one thousand distillations were made before tolerably constant 

 boiling-points were secured. In order to perform the operation successfully, two 

 series of bottles are required, one for the series being distilled, and the other for the 

 series distilling. As many bottles are necessary as there are 10-degree fractions to 

 be obtained. Thus, supposing the fluid, when first distilled, came over between 100 

 and 200, and it has been determined to obtain 10-degree fractions, the receiver is to 

 be changed for every 10 that the mercury rises. Thus, 10 bottles will be required 

 for the fractions distilling, and the same number for the fractions being distilled into. 

 The operation will be commenced by putting the original fluid (dried carefully witli 

 chloride of calcium or sticks of potash) into a retort capable of holding at least half 

 as much more fluid as the quantity inserted. Through the tubulature passes a pierced 

 cork, supporting a thermometer, the lower end of which should not dip into the fluid. 

 To the neck of the retort is adapted a good condensing arrangement, so placed 

 that the bottles can be placed beneath the exit-pipe. All the bottles having blank- 

 paper labels attached, the distillation is to be commenced. The first signs of distilla- 

 tion are to be watched for, but no fluid is to be separately received as an individual 

 fraction until boiling has commenced. As soon as it is found that the mercury indi- 

 cates 10 more than the temperature at which the distillation commenced, the bottle 



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