DYE WOODS AND MATERIALS 415 



MANUFACTURE OF DYESTUFFS 



Most of the natural dyes are now produced from imported woods from 

 Central and South America and the West Indies, the coloring matter 

 being obtained from the parenchyma cells by extraction after reducing 

 the wood to the powdered or chipped form. Dye woods generally con- 

 tain only from 5 to 10 per cent of their weight in true dye color. The 

 principle of wood dye extract operations consists first hi removing the 

 coloring material by lye washing made with the help of a suitable sol- 

 vent, which differs with each wood to be treated, and then by concen- 

 trating the solution to the crystal, liquid or powdered form. The 

 process employed in deriving these extracts varies with most of the large 

 manufacturing concerns and the details are held with the greatest 

 secrecy. However, the following is a very brief description of the 

 process generally used in the reduction of our principal dye woods. 



The wood is first run through a grinder or a very fine chipper or " hog." 

 In the case the latter is used the chips are again shredded. The principle 

 involved in reducing the wood to such fine proportions is to make the 

 coloring material more readily available to the effects of the solvent which 

 is used to separate and carry off the desired color from the wood cells. 

 The chips or shredded wood are then submitted to a curing process, which 

 consists of leaving them piled up in heaps 4 or 3 ft. in height in the open 

 air. The piles are moistened with water from time to time and left in 

 this condition for from four to six weeks. They are occasionally worked 

 over with shovels to prevent heating and to allow full access to the air. 

 The wood gradually turns to a deep color and sometimes certain chem- 

 icals are used to hasten the curing process. However, there is danger of 

 over-oxidation. Extraction and concentration are next followed out. 

 Extraction is accomplished in diffusion batteries consisting either of a 

 set of open tanks or of closed copper extractors arranged in series. Ordi- 

 narily there are eight or ten of these batteries, the liquor from one cell 

 being used as a solvent for the material in the next cell so that as con- 

 centrated a liquor as possible is obtained with a minimum amount of 

 extracting water. The liquid extract is then evaporated in multiple- 

 effect vacuum evaporators made expressly for this purpose. In this way 

 an extract is obtained containing about 25 to 30 per cent of total solids 

 at a temperature which is not injurious to the extract. All natural 

 dyestuffs require a mordant, such as a solution of chrome for their proper 

 fixation on fibers. 



