NAPHTHA, COAL. 



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NAPHTHA, CO All. Ordinary coal-naphtha is the first product in the distillation 

 of coal-tar. The latter is placed in large iron stills, holding from 800 to 1,500 gallons, 

 and distilled by direct steam. The first distillate is about 850 S. G. When 950 

 S. G. is made, all the naphtha or light oil is obtained. The distillate from 950 to 

 1000 S. G. is the middle oil; above that to about 106 S. G. is the heavy oil. 



The residue obtained in the first distillation is run off into cisterns or tar ponds to 

 allow of the removal of the water. This residue is called boiled tar. Pitch oil may 

 be obtained from it by distillation by the naked fire, every 1,000 gallons will yield 

 about 320 gallons of pitch oil. The residue of pitch in the still is run out while in a 

 melted state. The rough coal-naphtha contains a great number of impurities of 

 various kinds ; the principal cause of the foul odour being the organic bases described 

 in the article NAPHTHA, BONE. To remove these the naphtha is transferred to large 

 cylindrical vessels lined with lead. These vessels contain a vertical axis passing 

 down them, supporting blades of wood covered with lead, and pierced with holes. 

 The axis or shaft has, at its upper end, a crank to enable it to be rotated. The naphtha 

 having been run into the vessel, sulphuric acid is added, and the shaft with its blades 

 made to revolve. By this means the naphtha and acid are brought into intimate 

 contact. The whole is then allowed to settle, and the vitriol which has absorbed most 

 of the impurities, and acquired, in consequence, a thick tarry consistence, is run off. 

 This acid treacly matter is known in the works as ' sludge.' The naphtha floating 

 above the sludge is then treated a second time with acid, if the naphtha be required 

 of good quality. During the process, the naphtha acquires a sharp smell of sulphurous 

 acid, and retains a certain amount of sulplruric acid in solution. The next process is to 

 treat it with solution of caustic soda to remove these impurities. This may be effected 

 in an apparatus similar to the first. The naphtha, after removal of the caustic liquor, 

 is next run off into a still, and rectified ; it then forms the coal-naphtha of commerce. 



Coal tar of commerce is derived mainly from the rich cannels, or from the tars made 

 from coal in the London gas-works, or from the gas-works of the English towns. The 

 latter tar is richer in naphtha than the London ; while the tar from the Scotch cannels 

 yields from seven to thirteen per cent, of crude naphtha of a specific gravity of about 

 930, which is blown from it by steam introduced into the still. A still containing 

 2,500 gallons of the other tars would yield on au average forty gallons. 



The commercial value of naphtha has fluctuated since the extensive introduction of the 

 coal-tar colour industries, according to their varied fortunes during the last twenty years. 



The more or less volatile varieties were sought after just as the varied shades of 

 aniline, the manufacture of which they suited, headed the market. By a series of 

 fractional distillations, both with wet and dry steam, washings with sulphuric acid 

 (specific gravity 1'845), a series of naphthas, more or less rich in benzole, and con- 

 taining other valuable products are obtained. The naphtha which flows over at 

 a temperature up to 204 Fahr. is called 90 per cent, benzole ; that flowing between 

 204 and 210, is designated 80 per cent, benzole, and is again fractionally distilled 

 up to 204 ; while the residue, on being treated with high-pressure steam, yields a 

 quantity of 40 per cent, naphtha. 



Subjecting a charge of 1,587 gallons of crude naphtha and light oil to the series of 

 operations indicated, we obtain, first 897 gallons of once-run naphtha, and 56 gallons 

 of the last runnings, the remaining 634 gallons being only fit to mix with dead oil. 

 The 897 gallons of once-run naphtha yields, after purification by sulphuric acid, 301 

 gallons of 90 per cent, benzole, 195 gallons of 40 per cent, 237 gallons of solvent 

 naphtha, 12 gallons of last runnings, and 152 gallons of residuum. 



The 40 per cent, naphtha contains also toluol and xylol, and is most suitable for 

 making aniline red ; the 90 per cent, variety is best adapted for the manufacture of 

 aniline blue or black. 



In describing coal-naphtha, we shall take a cursory review of the nature and 

 properties of most of the substances produced by the distillation of coal-tar. It will 

 bo unnecessary here to enter into a minute description of the acids existing in coal- 

 tar, inasmuch as they have already been treated of in the article CARBOLIC ACID. 



On the hydrocarbons of coal-naphtha. The following are the principal constituents 

 of those coal-naphthas the boiling-points of which range between 190 and 350 : 



