358 



The World's Commercial Products 



Other well-known yellow dye-stuffs are Persian Berries, the unripe berries of a species of 

 Rhamnus growing in Southern Europe, The Levant, Asia Minor, and Persia; Quercitron 

 Bark, from a species of oak indigenous to the United States ; Weld ; Turmeric, which is 

 largely grown in India; and Annatto, so widely cultivated in tropical countries. . 



Archil, Cudbear, and Litmus 



These three products are obtained from a number of different lichens imported from Ceylon 

 and Mozambique, the most important being Roccella tinctoria and Lecanoria tinctoria, which 

 possess the property of producing a violet-blue dye when exposed to the joint action of 

 ammonia and air. For the preparation of archil the lichens are simply sprayed with a 

 solution of ammonia and exposed to the air. When the dye is fully developed, the mass of 

 lichens is extracted with water forming " archil liquor," or the latter may be evaporated 



to dryness forming 

 ■ "cudbear." If the 

 treatment of the lichens 

 with ammonia is long- 

 continued and lime is 

 eventually added to the 

 mass .before extraction 

 with water, the purple 

 dye "litmus" is ob- 

 tained. This is usually 

 sold mixed with chalk 

 or powdered gypsum. 

 Archil is used in wool 

 and silk dyeing to 

 produce purple colours. 

 Litmus is used in 

 chemistry for the de- 

 tection of acids and 

 alkalis; its natural 

 purple tint is changed 

 to vivid red by acids 

 and to deep blue by 

 alkalis. 



By permission of Messrs. John /akson & Co., West Croydon 



GATHERING MINT 



ESSENTIAL OILS 



The descriptive term " volatile " serves to differentiate these products from the " fixed " 

 oils, which do not evaporate on exposure to air. The older name " essential " indicates that 

 they are " essences," i.e., the constituents to which the plants containing them owe their 

 peculiar properties, thus, the characteristic aroma and flavour of the well-known spice, cinna- 

 mon, are due to the essential oil it contains, and this oil, possessing in a far higher degree the 

 aroma and taste characteristic of cinnamon can be extracted from the spice, leaving a material 

 devoid of odour and flavour. 



Volatile oils are usually prepared by a process of distillation in steam. For this purpose 

 the materia] to be operated upon is ground, placed in a copper still, covered with water, and 

 allowed to stand for some hours. The still is then..heated so that the water boils, producing 

 steam, which carries away in a state of vapour the volatile oil contained in the plant, and this 

 mixture of steam and oil vapour passes into the condenser attached to the still, where it forms 

 water with a layer of oil floating on it. When the whole of the available oil has been procured 

 in this way it is skimmed off the water and filtered. 



