90 Prof. R. Bunsen on Flame Reactions. 



upon it when the basin is cooled; the colour then either changes 

 or entirely disappears, the film being dissolved in the moisture of 

 the breath. If the basin be gently warmed, or if it be blown 

 upon for some distance, the film again becomes visible by the 

 evaporation of the moisture in the current of air. 



(@) The ammonia compound of the iodide is formed by blow- 

 ing ammoniacal air upon it and noticing whether the colour of 

 the thick and thin films alters quickly, slowly, or not at all. The 

 different colours reappear at once if the basin be held for a few 

 moments over an open bottle containing fuming hydrochloric 

 acid. 



(7) The iodide-films generally give the same reactions as the 

 oxide-films with silver-nitrate and ammonia, with stannous chlo- 

 ride, and with caustic soda. 



(d) The sulphide-film is most easily obtained from the iodide- 

 film by blowing upon it a current of air saturated with ammo- 

 nium-sulphide, and removing the excess of sulphide by gently 

 warming the porcelain. It is advisable to breathe on the film 

 from time to time whilst the current of sulphuretted air is being 

 blown on the basin. The experiments to be made with this film 

 are: — 



(a) The solubility or otherwise in water is ascertained by 

 breathing on to it, or by addition of a drop of water. The sul- 

 phides often possess the same colour as the iodide-films; they 

 may, however, generally be distinguished by their insolubility on 

 breathing. 



(/3) The solubility of the sulphide in ammonium-sulphide is 

 ascertained by blowing or dropping. 



4. Films on Test-tubes. — Under certain circumstances it is 

 advisable not to collect the film on porcelain, but upon the out- 

 side of a large test-tube (fig. 5, e) ; this method is especially used 

 when it is needed to collect larger quantities of the reduction 

 film for the purposes of further examination. The fine asbestos- 

 thread with the sample of substance is held on the glass tube (b) 

 before the lamp so that it is placed at the height of the middle 

 of the upper reducing flame, and the test-tube fixed so that the 

 lowest point is just above the end of the asbestos-thread. If the 

 lamp be now pushed under the test-tube, the substance and the 

 asbestos- thread are in the reducing flame. By repeating this 

 operation the film can be obtained of any wished-for thickness ; 

 some pieces of marble are in this case placed in the test-tube, to 

 prevent the water from being thrown out of the tube by percus- 

 sive boiling. 



III. The Reactions of the Elements. 

 The elements, which can easily be recognized by their flame 



