482 If. Carey Lea — AUotropic Silver. 



faint green tinge, while still higher we find the light purple 

 tint of the Bunsen flame. The appearance of this flame in the 

 mirror clearly indicates what is taking place. The mass of gas 

 above the contracted place, after being ignited by a flash from 

 the continuously burning tube, does not immediately go out. 

 The flame fights its way down the ascending column, but con- 

 tinually loses ground, owing to the great velocity of the jet. 

 The second flash comes often before the tip of the first one has 

 gone out. and if the interval is short enough the flashes will 

 mingle. In £.g. 7, I have attempted to show this in a clearer 

 manner. The series shows an interval of one flash, the figures 

 representing instantaneous views of the flame at successive 

 moments of time, Tigs. A to E show the gradual dying out of 

 the flame of the first flash. At F the second flash has com- 

 menced, and at H it has risen and mingled with the last vestige 

 of the first. 



By carefully regulating the pressure, we may give to the jet 

 a velocity which shall equal the speed of combustion for the 

 mixture of gas and air. The flame will now hang balanced in 

 the air. as shown in fig. 8, the tendency of the fire to spread 

 downward being exactly neutralized by the upward motion of 

 the column. On examining this flame the cause of the bright 

 blue and faint green lines in the mirror is discerned. Around 

 the base of the flame the mixture burns with an intense blue 

 light (tig. 8 a) ; surmounting this is a cone of greenish fire B, 

 while above this the flame has a light purple tinge. 



Art. LVIII. — AUotropir Silver. Part III. Blue Silver^ 

 soluble wad insoluble Farms y by M. Carey Lea. 



When my first paper on the subject of allotropic silver was 

 published about two years ago, that substance seemed to be the 

 result of a very limited number of reactions closely allied to 

 each other. Further study has shown that it is a much more 

 common product than at first appeared to be the case. Wher- 

 ever in the reduction of silver a reddish color shows itself, 

 that may be taken as a probable indication that allotropic silver 

 has been formed, even although it may be destroyed before it- 

 can be isolated. 



"What is rather remarkable is that allotropic silver is pro- 

 duced abundantly in certain very familiar reactions in which 

 its presence has never been suspected : so abundantly in fact 

 that some of these reactions constitute the best methods of 

 obtaining silver in the soluble form. In photographic opera- 

 tions silver has often been reduced by tannin in the presence 



