742 AMYLACEOUS AND SACCHARINE SUBSTANCES. 



cording to Fritzsche, when water saturated with bromine is 

 dropt into a solution of starch in water acidulated with hydro- 

 chloric acid. The colour is destroyed by a slight heat; to 

 obtain the iodide of starch in a state of purity the following 

 process is recommended. A firm jelly is prepared by boiling 

 potato starch with water, and after cooling, a quantity of 

 hydrochloric acid is added sufficient to occasion the mixture 

 to become liquid when assisted by a slight elevation of 

 temperature. The solution is then filtered and a solution 

 of iodine in alcohol is mixed with it, so long as the latter 

 produces a blue precipitate, care being taken not to add too 

 much of the solution of iodine, as the alcohol of that solu- 

 tion will then precipitate uncombined starch. The precipitate 

 is collected, drained on a filter and washed with water 

 poured upon it in small quantities. Once deprived of hydro- 

 chloric acid, the compound dissolves in the water used to wash 

 it; the washing is therefore interrupted so soon as the liquid 

 which passes exhibits an intense blue colour ; the compound is 

 removed from the filter and dried on a capsule over sulphuric 

 acid in vacuo. A brown-black gummy and very brilliant mass 

 is thus obtained, which can easily be pounded when perfectly 

 dry, but which becomes viscous by attracting hygrometric 

 moisture. It is very easily dissolved by water, giving a deep 

 blue solution, and may be recovered again by evaporation in 

 vacuo, in a dry state and without alteration. When a solution 

 of iodide of starch is heated, it becomes colourless at 158 or 

 160 if very dilute, but not under 194 when the solution is 

 concentrated. The colour reappears on the cooling of the 

 solution, provided it has not been boiled. When the colour is 

 not restored, the iodine appears to be converted into iodic and 

 hydriodic acids. Animal charcoal discolours the blue solution, 

 carrying down iodine. The iodide of starch contains 41.79 parts 

 of iodine with 58.21 of starch, according to the analysis of 

 Lassaigne, or it consists of two atoms of iodine with one atom 

 of starch. (Berzelius). 



Dextrin or mucilaginous starch. By the action of acids, 

 alkalies, diastase, and of heat, a complete dissolution of the 

 gelatinous starch may be effected ; it becomes largely soluble in 

 cold water, the solution is mucilaginous and not gelatinous, and 

 the altered starch has many of the characters of gum. Dextrin 



