ANIMAL CHARCOAL. 243 



solutions gradually remove the dissolved matter from the fluid. 

 This action may be brought about in a variety of ways, the most 

 usual one being where some kind of chemical action is set up with 

 the result of precipitating the dissolved matter in the form of 

 an insoluble compound. The ordinary processes of dyeing are 

 amongst the best examples of this class of action : if textile 

 fabrics (wool, silk, or cotton prepared or " mordanted " in various 

 ways) are placed in a dye vat (i.e., a large tank filled with solution of 

 colouring matter) the fibres of the fabric combine with the colour 

 and remove it from solution, becoming themselves increased in 

 weight and tinted by the operation. But besides this chemical 

 action, some substances, and especially various kinds of charcoal, 

 have the power of withdrawing from solution certain dissolved 

 matters and storing them up in their pores, no chemical action 

 at all taking place, at any rate in the sense in which the term is 

 usually understood. 



Thus charcoal, especially "animal charcoal" from bones, &c., 

 when boiled with water containing small quantities of strychnine 

 and similar substances, will absorb them and remove them from 

 solution ; on drying the charcoal and boiling it with alcohol the 

 absorbed substances are dissolved out again, and may be obtained 

 from the solution by evaporating off the spirit. This process for 

 separating certain bodies of this kind from beer or such like liquids, 

 is employed in their analytical examination in cases of suspected 

 adulteration, poisoning, &c. Obviously it is closely akin to the pro- 

 cess of separation of one substance, dissolved in a solvent, by adding 

 another solvent in which the substance dissolves more freely, the 

 two solvents not being miscible together in all proportions. 



Thus in Expt. 62 an aqueous solution of iodine when agitated 

 with chloroform, gives, on standing, two layers of fluid; the 

 upper one water containing but little iodine, the lower one chloro- 

 form which has dissolved out almost all the iodine from the water. 



Similarly (Expt. 86), when zinc is agitated with a melted 

 mixture of lead and silver, a lighter alloy floats up, consisting of 

 the majority of the zinc with a little lead dissolved therein, and 

 practically all the silver ; whilst the heavier alloy consists of the 

 greater part of the lead with a little zinc dissolved therein, but 

 only a very small fraction of the silver originally present. Ether 

 behaves in a similar fashion when agitated with aqueous solutions 

 of certain vegetable products ; these substances are removed almost 

 entirely from the water, being dissolved in the ethereal fluid 

 which rises to the top on standing. 



The dark colouring matter produced by heating sugar is readily 

 absorbed by charcoal, although pure sugar itself is but little affected ; 



