E. L. Nichols — Age-coating in Incandescent Lamps. 285 



The curves in figure 2 are based upon these data. They 

 show that the loss in candle-power and efficiency are only in 

 part due to the opacity of the coatings. It is of some interest 

 to compare lamps 2 and 10, since the former is a three watt 

 lamp, whereas the other required 5*16 watts per candle at the 

 beginning of the test. It is to be regretted that the tests did 

 .not extend over the normal life-time of such a lamp ; the 

 results obtained, however, suffice to show that the loss due to 

 coating is a much larger portion of the total loss in the low 

 efficiency lamp than in the other. Measurements with several 

 lamps, maintained at abnormally high temperatures seemed to 

 indicate that the higher the state of incandescence the less 

 marked (relatively) is the influence of the age-coating upon 

 the decadence of the lamp. 



Summary of results. 



1. The rate of deposit of the coating in incandescent lamp 

 bulbs is greatest in the early part of the life of the lamp. 

 For example, in the case of a lamp which lasted 800 hours, 

 (see Table III) more than half of the coating was deposited dur- 

 ing the first 200 hours. 



2. The loss of brightness due to the absorbing power of the 

 age-coating is a variable part of the total loss, being greatest 

 in lamps of high initial efficiency. 



3. The coating does not appreciably modify the character of 

 the light which emanates from the lamp. 



4. The distribution of the coating within the bulb is a nearly 

 uniform one (see figure 1). 



5. No marked difference between treated and untreated fila- 

 ments appears to exist, as regards the density or quality of the 

 coating produced from them.* 



Physical Laboratory of Cornell University, July, 1892. 



* Since this article was written it has been pointed out by Professor B. F. 

 Thomas (in the paper already cited), that in the case of lamps exhausted without 

 the aid of mercury the age -coating is scarcely perceptible. 



