SCIENCE NOTES.

Digger (Invercargill RSA), Issue 30, 8 October 1920, Page 6

SCIENCE NOTES.

THE TREASURES OF . COAL-TAR. If you put a bit of soft coal into a test-tu.be (or, if you haven't a iest-tube, into a clay tobacco pipe, and cover it over with clay) and heat it, you will find a gas coming out at the end of the tube, that will burn with a yellow smoky llame. After all the gas comes off you will find in the hottom of the test-tuhe a chunk of dry, porous coke. These? then, are the two main products of the destructive distillation of coal. But if you are a born chemist, with an eye to by-products, you will notice along the middle of th.e tube, where it is neither too hofc nor too cold, some dirty drops of water and some black, sticky stuff. If yoe are just an ordinary person you won't pay any attention to this, because there is only a little of it, and because what vou are after is the coke and gas. You regard the nasty smelly mess that comes in between as merely a nuisance, because it dogs up and spoils your nice clean tube. Now, that is the way the gas-makers and coke-makers — being for the most part ordinary persons, and not born chemists — used to regard the water and tar that got into their pipes. They washed it out so as to have the gas clean ,and then ran it into the creek. But the neigh--bours — especially those who ftfehed m the stream below the gas-work.s— made a fuss about spoiling the water, so that the gas-men gave away the tar to the boys for bonfires or sold it for roofing. But this same tar, which for a hnndred years was thrown away, and nearly half of which is thrown away yet in the1United States, turns out to he oue of the most useful things in the world. Itis one of the strategic points in war and commerce. It wounds and heals. It supplies munitions and medicin.es. It is like the magic purse of Fortunatus? from which everything vLshed for could be drawn. The chemist puts his hand into the black mass and draws out all the colours of the rainbow. This evfl-smelling substance beats the rose in the production of perfume, and surpasses the honeycomb in sweetness. It is interesting to recall that anaesthetics like novocaine and stovaine are derived from coal-tar; anti-pyretics like aspirin, acetanilid, and acetphenetedin ; specifics such as a-drenaline prescrfbed for Addison's disease, soamin and arsacetin for sleeping sickness, salvarsan for blood disease, and phenolphthalein used as a laxativ.e. Saccharin. dulcin, and . other sweeteners are obtained from the same source; essences like cinnamon and coumarin ; photographie develophers of various kinds ; lyllite, melinite, and trinitrotoluol (called TNT for short), which did • such destructive work on the battlefront in Europe. So diverse are the products that it seems incomprehensible that all can be found in one original product. In the distillation of coal-tar we obtain from the light oil such products as benzol, totuol, xylol, pyridine, phenol, and cresol. From the middle oil we get napthalene( and from the heavy oil com.es anthracene. The refined tar and the pitch left as a residue have their uses. Grsat industries have been built upon each and every one of these r.emarkable products, and the chemists have only begun their work in this line. The future is full of possibilities.