220 SCIENTIFIC AMUSEMENTS. 



when nearly dry carefully broken tip into small fragments by 

 chopping with a blunt knife and rubbing in a mortar ; even when 

 completely dry the mixture will not be as effective as machine- 

 made powder, and when fired in the form of a train will not go 

 off as rapidly, but more like the composition in a squib, which is 

 very much the same as ungrained powder. The chemical action 

 aking place when powder explodes is much the same as when 

 charcoal and sulphur are thrown into melted saltpetre, these 

 combustible bodies burning by the aid of the oxygen derived from 

 the saltpetre and suddenly producing a large volume of gas in so 

 doing (vide Expt. 258). 



Expt. 260. A Mixture that detonates when struck. Care- 

 fully powder a few crystals of potassium chlorate in a clean dry 

 mortar ; turn the powder on to a sheet of paper, add to it about 

 half its bulk of flowers of sulphur and mix the two by pouring 

 the powders from one paper to another and back again several 

 times, taking special care to avoid all rubbing witli heavy substances. 

 Place a few grains of the mixture in a mortar and rub with the 

 pestle ; a smart crack, or succession of cracks will be heard ; place 

 a pinch on an anvil and strike it with the flat face of a hammer ; 

 a loud report will be produced. 



Caution. Never prepare this mixture by rubbing together 

 crystals of potassium chlorate and sulphur so as to pulverise the 

 former whilst mixing the two ingredients ; if this be done the 

 mixture will probably explode and painful cuts be produced or 

 damage done to the eyes by solid pieces of crystallised chlorate 

 being projected about in all directions. Further, never prepare 

 the mixture in larger quantities at once than one or two good- 

 sized pinches of chlorate crystals, say J ounce at the most. 



Expt. 261. To prepare Coloured Fires. The materials em- 

 ployed by firework makers for preparing coloured fires are usually 

 more or less of the nature of gunpowder, containing saltpetre and 

 sulphur with other substances giving a colour to the flame pro- 

 duced when the composition is fired. Blue fire (for Bengal lights) 

 can be prepared by powdering separately and then well inter- 

 mixing together 4 parts of saltpetre, 2 of sulphur, and 1 of sulphide 

 of antimony. Red fire, can be similarly made by mixing 8 parts 

 of well dried nitrate, of strontium, 2 of saltpetre, 2 of sulphur, and 

 1 of powdered charcoal; and Green fire, by using nitrate of barium 

 instead of nitrate of strontium. Makers often use chlorate of 

 potassium as an ingredient, which causes the composition to burn 

 better; but the mixture is unsafe on account of the explosive 

 properties of potassium chlorate mixed with sulphur (Expt. 260). 



What are sometimes sold under the name of "Lightning papers" 



