226 ANNUAL OF SCIENTIFIC DISCOVERY. 



Until the last few years, the applications of coal-tar were very simple, and 

 very limited : it was spread over a vast variety of substances which required 

 its preserving influence to guard them from the weather; it was used as a 

 rough varnish for gigantic ironwork ; and it formed an important ingredient 

 in various compositions used instead of stone for esplanade purposes. 



Coal-Jar is a union of a very considerable number of organic bodies, some 

 being solid, and others fluid. It contains if you desire a clear and satis- 

 factory idea of its composition ammonia, aniline, picoline, quinoline, pyri- 

 dine, phenic acid, rosalic acid, brunolic acid, benzole, toluole, cumole, cy- 

 mole, napthaline, paranapthaline, chrysene, and pyrene. As each of these 

 sixteen substances is individually more or less complicated, we are not, we 

 think, wrong in saying that the fluid formed by their union is somewhat 

 remarkable. 



The apparently simple business of the tar-worker is to take his tar to 

 pieces ; not to separate it into all the various components we have enumer- 

 ated, for that would be a very difficult, and perhaps useless proceeding, but 

 to extract from it a number of vastly different bodies, which have been put 

 to a variety of uses in the manufacturing world. 



In nearly the whole of his operations, the simple agent used by the tar- 

 worker is heat. It is one of the fundamental laws of chemistry, that every 

 fluid at a certain temperature shall assume a gaseous form; the temperature 

 at which such change takes place being entirely dependent upon the nature 

 of the fluid operated upon. The highly complex body, tar, is therefore 

 placed in certain large stills, each containing from 2000 to 3000 gallons ; and 

 heat being applied, the tar in time begins to boil; and each of its fluid con- 

 stituents, which assumes the form of vapor at a different temperature from 

 the others, separately makes its appearance at the end of the still-worm. 



The first of these is a quantity of ammonia and other gases, all of which 

 are collected in cold water, which soon becomes strongly impregnated with 

 them, and is used for the preparation of a rough description of sulphate of 

 ammonia, which finds a ready sale as an important ingredient in certain, 

 artificial manures. 



As the heat is increased, an oily fluid comes over, technically called " light 

 oil," which is carefully collected apart from the other products. When as 

 much of this light oil has made its appearance as about equals in bulk one- 

 twentieth of the tar originally put into the still, it ceases to be produced, and 

 is succeeded by a dense, dark-colored fluid, with a peculiarly offensive odor, 

 known as " dead oil." The dead oil comes over in much larger quantity than 

 the light oil, equalling fully one-fifth of the tar. When the dead oil has ceased 

 to run, the distiller knows it is of no use to keep the pot boiling any longer; 

 the fire is therefore put out, a huge tap at the bottom of the still is turned, 

 and the thick, black residuum, still fluid in its heated state, being neither 

 more nor less than common pitch, is allowed to run along certain channels, 

 prepared for its transmission, into immense underground tanks in which it 

 is stored. 



By simple boiling, then, our manufacturer has split up his tar into four very 

 different matters pitch, dead oil, light oil, and ammoniacal liquor. 



With the pitch he does very little. Shortly after running from the still, it 

 is ladled out of the great tanks already mentioned into moulds formed of 

 the halves of resin-casks, rubbed with chalk on the inside to prevent its 

 adhering; and being sold in this state, it is used for a variety of well-known 

 purposes. 



