COLOURED FIRES. 221 



are pieces of tissue paper that have been converted into a highly- 

 inflammable substance resembling guncotton (by dipping them 

 into nitric acid mixed with sulphuric acid, and washing) and 

 subsequently impregnated with certain salts, giving the colour to 

 the flame; e.g., strontium chlorate for red, and barium chlorate for 

 green. These burn with a bright flash of light when a flame is 

 applied; whilst no particular danger attends the burning of small 

 strips of such prepared papers, they are highly dangerous to keep 

 in any quantity, on account of the ease with which they can be 

 ignited. Many such compositions as red fire, &c., sometimes 

 possess the power of taking fire spontaneously, especially when 

 kept in a warm place ; several fires in theatres and similar places of 

 entertainment are believed to have been thus caused. 



Expt. 262. To Deodorise Sulphuretted Hydrogen. Into a jar 

 full of air pass a few bubbles of sulphuretted hydrogen (Expt. 

 145), whereby a foetid smell will be communicated to the air. 

 Pass in a few bubbles of chlorine (Expt. 180); the smell of sul- 

 phuretted hydrogen will disappear, and the air will no longer 

 blacken a strip of paper soaked in nitrate of lead solution (Expt. 

 14). Chlorine decomposes sulphuretted hydrogen, combining with 

 the hydrogen therein contained (forming hydrochloric acid gas) 

 and setting free sulphur. If sufficient sulphuretted hydrogen is 

 present in the jar, the action of the chlorine will give rise to the 

 deposition on the sides of a film of solid sulphur, easily visible ; 

 whilst by introducing a spoonful of water into the jar and shaking 

 up, a weak solution of hydrochloric acid will be obtained which 

 will redden blue litmus paper (Expt. 57). 



The use of "chloride of lime" or bleaching powder as a 

 deodorising agent for evil-smelling drains, &c., is based upon very 

 similar changes thereby produced in the foul gases evolved. 



Production of Gases by the Chemical Action of Solids 

 on one another. 



As a general rule chemical action does not take place readily 

 between substances unless one or both are rendered fluid, either by 

 applying heat so as to melt the body, or by dissolving in some 

 solvent ; but there are some exceptions to this rule. 



Expt. 263. To develop a Gas by heating two Solids 

 together. Take as much slaked lime (Expt. 240) as will lie on a 

 shilling and mix with it as much powdered salammoniac (chloride 

 of ammonium). Put the mixture into a clean dry test-tube and 

 heat in the Bunsen lamp flame. Ammonia gas will be copiously 

 disengaged, as may be proved by smelling cautiously (taking care 



