154 SCIENTIFIC AMUSEMENTS. 



Calico as prepared by spinning and weaving from cotton is not 

 perfectly white, but is rendered so by bleaching it in just the same 

 way ; a bath of " bleach liquor," or solution of bleaching powder, 

 is prepared and the calico dipped into it, being unwound from a 

 large roll, and gradually passed through the liquid. After passing 

 through the bath, the calico is then similarly passed through a 

 second vat containing water with a little sulphuric acid dissolved 

 therein ; the goods thus " soured " become whitened by the action 

 of the chlorine set free ; after washing with water to remove acid, 

 they are far less brownish tinted than at first. In the same kind 

 of way fruit or wine stains may be removed from a tablecloth by 

 bleaching them out with a solution of bleaching powder applied to 

 the stain, a little vinegar or other weak acid solution being 

 subsequently also applied, and the cloth finally rinsed in plain 

 water. 



Expt. 164. To turn a colourless Liquid Blue by means of 

 Chlorine Solution. Get as much starch as will lie on a sixpence, 

 and mash it up with a dessert-spoonful of water to a cream in a cup 

 by means of a spoon. Boil half a tumblerful of water in an evapor- 

 ating basin, and whilst boiling stir in the cream of starch. The 

 solid white particles of starch will become a thin jelly with the 

 boiling water, forming the material used by laundresses to stiffen 

 collars and shirts, &c. When the starch-jelly is cold pour a 

 little into a tumblerful of water, and add a few drops of solution of 

 iodide of potassium; finally drop in a little chlorine solution, and 

 stir up. A beautiful blue colour will be produced, owing to a 

 chemical action taking place ; the end result is the formation of 

 " iodide of starch," a blue compound produced by the combination 

 of starch with the iodine contained in the iodide of potassium, and 

 set free therefrom by the action of the chlorine. If too much 

 chlorine be used, the blue liquid becomes browned. 



The blue liquid thus formed possesses a very curious property ; 

 if a little of it be boiled in a test-tube, the blue colour will dis- 

 appear as the liquid gets hot ; but on cooling again the blue tint 

 reappears. When the test-tube is heated to such a degree that 

 the blue colour has vanished, plunge the hot tube into a tumbler of 

 cold water so as to cool it rapidly : the blue will first appear at the 

 bottom of the tube, as this cools quickest (Chapter XX.), but will 

 speedily spread through the whole of the fluid. This experiment 

 will not succeed well if too much chlorine-water have been used 

 so as to brown the liquid. 



The preceding two experiments may be combined together so 

 as to produce a curious effect. Prepare two glasses of water, one 

 containing a small quantity of indigo solution so as to tint it blue, 



