Accidental and Complementary Colours. 293 



by receiving it first upon white paper, and then upon 

 coloured paper; as, for example, boracic acid in alcohol 

 yields a fine light green flame, the shadow is pink on white 

 ground, violet on blue ground, orange on yellow, &c. If 

 a sheet of white paper be held before the red light from 

 a coke fire, and the hand be placed between the paper and 

 the fire, the resulting shadow will be green. On a dull 

 day, or just after sunset, a coke fire or the red part of a 

 coal fire throws green shadows in various parts of the room. 

 A w^hite screen placed parallel with the window, the fire 

 being between, is an excellent ground for the reception of 

 the shadows. Chairs, or any opaque objects, the shadows 

 of which are cast by the fire upon the screen, are strongly 

 green. This, and most of the observations with coloured 

 flames are most conveniently made immediately after sun- 

 set, or in a somewhat obscure room, or part of a room, as 

 the abundant presence of day light prevents the shadows 

 being appreciated. A little flat dish, containing the salt in 

 spirit, should be placed on white ground, and the shadow 

 of the dish will be complementary in colour to that of the 

 flame. Or, a sheet of white paper may be held between 

 the eye of the observer and the flame, and the hand or 

 fingers between the flame and the white paper. If very 

 vivid flames be required, equal parts of chlorate of potassa 

 and white sugar may be employed mingled with one part 

 of a salt which communicates colour to the flame, such as 

 the muriates of barytes, strontia, soda, lime, &c. The in- 

 gredients should be well dried, and intimately mixed in a 

 mortar. A drop or two of sulphuric acid will fire the mix- 

 ture. This mode of impressing the eye is a pleasing one. 

 I have found the spectra to be very different with different 

 persons, and the impression on the retina lasts from two to 

 three minutes. Flames may also be obtained from gases, 

 such as carbonic oxide, equal parts of hydrogen and binoxide 

 of nitrogen, cyanogen, &;c. The purple flame of potassium 

 upon water may be employed, and if the metal be thrown 

 into ajar of carbonic acid standing over water, it will yield 

 a fine ruby, which is almost homogeneous. 



23. Class ^th. When a polished coloured surface is pre- 

 sented in an inclined position to the light, so that the 

 coloured rays proceeding from the surface be reflected upon 



