MANUFACTURE OF WOOD-VINEGAR. 239 



the crude product obtained by the distillation of the wood in the 

 retorts, and either brought into commerce as wood tar, or further 

 worked to obtain the substances occurring in it, such as illumina- 

 ting oils, carbolic acid, etc., or it is used in the manufacture of 

 wagon grease, lubricants, etc. 



Wood-vinegar can, however, not be entirely purified by distil- 

 lation nor by passing it over freshly glowed charcoal. Although 

 seven-eighths of it passes over entirely colorless, the product has 

 a strong empyreumatic taste and odor, gradually turns brown in 

 the air, and gives brown salts with bases. Stoltze has proposed 

 several methods for the purification of the rectified acid, the most 

 simple and cheapest being to add 5 pounds of finely pulverized 

 pyrolusite to every 100 quarts of acid, keeping it at nearly a 

 boiling heat for 6 hours, then digesting it in the same manner 

 with 40 pounds of freshly glowed charcoal pulverized and sifted 

 while hot, and finally distilling off to dryness in a shallow cast- 

 iron still. But on account of its tediousness and the necessary 

 large consumption of fuel this process, though frequently modi- 

 fied, has been almost entirely abandoned. 



According to Terreil and Chateau, the wood-vinegar is purified 

 by compounding it, according to its more or less dark color, with 

 10 or 5 per cent, of concentrated sulphuric acid, whereby the 

 greater portion of the tar separates in 24 hours. By distilling 

 the decanted acid it is obtained almost colorless, but it darkens 

 somewhat on exposure to the air, and by saturation with soda a 

 slightly colored salt is obtained which can, however, be discol- 

 ored with a small consumption of animal charcoal. 



Rothe employs a peculiar method for the purification of wood- 

 vinegar. The greater portion of the tar being separated by stand- 

 ing, the wood-vinegar with an addition of charcoal is rectified from 

 a copper still The pale yellow watery wood-spirit is caught by 

 itself, and the succeeding clear, but strongly empyreumatic, distil- 

 late is pumped into a vat placed at a considerable height from which 

 it runs into a purifying apparatus. The latter consists of a cylin- 

 drical pipe of strong tin-plate ; it is about 26 feet high and 1J 

 feet in diameter, and is filled with pieces of coke about 0.122 

 cubic inch in size, which rest upon a strongly tinned iron grate 

 placed about 1J feet above the bottom of the pipe. Over this 



