280 E. L. Nichols — Age-coating in Incandescent Lamps. 



" age-coating" as the deposit which we are considering may be 

 called, is therefore to dim the lamp, without appreciably chang- 

 ing the quality of its light. 



The most complete set of observations obtained with lamps 

 of untreated carbon are those referring to a lamp designated 

 in our list as No. 2." This lamp was maintained at normal 

 voltage for over eight hundred hours. Frequent readings of 

 candle-power and current, during this time, afforded the means 

 of tracing the progressive changes of light-giving power, 

 efiicienc}^ and resistance. Measurements of the age-coating 

 were made after 100, 200, 400 and 800 hours of life, readings 

 being taken in ten regions of the spectrum. The results are 

 given in Table I, together with data indicating the condition 

 of the lamp at the above mentioned periods of its life. These 

 are taken from a set of sixty-seven readings of voltage and 

 current, distributed over the entire life of the lamp at nearly 

 equal intervals. The variation in voltage during the entire 

 eight hundred hours was never more than 0*3 volts above or 

 below the initial value. 



Table I. 



Lamp No. 2 (untreated filament). 



Initial Conditions. 



Yolts. Amperes. Ohms. Candle-power. Watts per candle. 



101-8 0-474 214-8 16-00 3-015 



Conditions after 100 hours. 



Yolts. Amperes. Ohms. Candle-power. Watts per candle. 



101-9 0-453 225-3 12-50 3"697 



Light transmitted by the coating, after 100 hours. 



A = -750 88-9 per cent A = -507 92-2 per cent 



•713 90-2 -481 92-8 



•635 91-8 -460 923 



•658 91-5 -443 92'4 



•538 91-9 -429 92.4 



Conditions after 200 hours. 



Volts. Amperes. Ohms. Candle-power. Watts per candle. 



101-8 0-421 225-9 10-8 4-250 



Light transmitted by the coating after 200 hours. 



X = -750 83-5 per cent A = -507 86*4 per cent 



•713 84-5 -481 86-9 



•635 85-6 -460 87"6 



•580 85-4 -443 87*9 



•538 85-9 -429 85'4 



* This and other numbers used refer to the records of these experiments as 

 given in full in the thesis of Messrs. Moore and Ling, a manuscript deposited in 

 the library of Cornell University. (The Life and Duration of Incandescent 

 Lamps ; with special Reference to the Light absorbed by the Coating within the 

 B*ulb, by B. B. Moore and C. J. Ling. 1890.) 



