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form appears as a fine, deep blue powder. It is in- 

 soluble in water, and but slightly soluble in alcohol : 

 its true solvent is sulphuric acid : 8 parts of sulphu- 

 ric acid dissolve 1 part of indigo ; and the solution 

 diluted with water forms a very fine blue dye. 



Indigo, by its distillation, affords carbonic acid 

 gas, water, charcoal, ammonia, and some oily and 

 acid matter : the charcoal is in very large proportion. 

 Pure indigo therefore most probably consists of car- 

 bon, hydrogene, oxygene, and azote. 



Indigo owes its blue colour to combination with 

 oxygene. For the uses of the dyers it is partly de- 

 prived of oxygene, by digesting it with orpiment and 

 lime water, when it becomes soluble in the lime water, 

 and of a greenish colour. Cloths steeped in this so- 

 lution combine with the indigo ; they are green when 

 taken out of the liquor, but become blue by absorb- 

 fng oxgene when exposed to air. 



Indigo is one of the most valuable and most ex- 

 tensively used of the dyeing materials. 



10. The narcotic principle is found abundantly in 

 opium, which is obtained from the juice of the white 

 poppy, (Papaver albuni). To procure the narcotic 

 principle, water is digested upon opium : the solution 

 obtained is evaporated till it becomes of the consistence 

 of a syrup. By the addition . of cold water to this 

 syrup a precipitate is obtained. Alchohol is boiled on 

 this precipitate ; during x the cooling of the alcohol 

 crystals fall down. These crystals are to be again 

 dissolved in alcohol, and again precipitated by cool- 

 ing : and the process is to be repeated till their colour 

 is white j they are crystals of narcotic principle. 



