486 INVESTIGATIONS RELATIVE TO ILLUMINATING MATERIALS. 



was greater than that of the sperm. These results were recognized as 

 having an important bearing on the question of the application of lard- 

 oil as a light-house illuminant. It only required to be burned at a high 

 temperature ; and as this could be readily obtained in the case of larger 

 lamps, there appeared to be no difficulty in its application. 



The previous trials had been with small lamps, with single solid wicks, 

 instead of the Fresnel lamp, with hollow burners. After these prelim- 

 inary experiments, two light- houses of the first order, at Cape Ann, 

 Massachusetts, separated by a distance of only 900 feet, were selected 

 as affording excellent facilities for trying, in actual burning, the correct- 

 ness of the conclusions which had been arrived at. One of these light- 

 houses was supplied with sperm and the other with lard oil, each lamp 

 being so trimmed as to exhibit its greatest capacity. It was found by 

 photometrical trial that the lamp supplied with lard exceeded in inten- 

 sity of light that of the one furnished with sperm. The experiment was 

 continued for several months, and the relative volume of the two ma- 

 terials carefully observed. The quantity of sperm burned during the 

 continuance of the experiment was to that of lard as 100 is to 104. 



The freezing temperature of lard-oil depends upon the temperature 

 at which it was expelled by pressure from the animal tissues in which it 

 was contained. It is higher however than the freezing temperature of 

 sperm, on an average of from 3° to 4°, but this is a matter of no jirac- 

 tical objection to the substitution of lard for sperm, since the heat 

 evolved from an Argand lamp is, in cases where the draught passes 

 through the reserv^oir, sufficient to keep the lard liquid even during the 

 lowest external temperature. Indeed, the small difference in tempera- 

 ture in freezing of the two oils is a matter of little moment, in cases 

 which frequently happen when the temperature of the atmosphere is 

 l)elow zero on the Fahrenheit scale. At such a temperature, both oils 

 would become alike solid, unless some means were aflbrded for i^revent- 

 ing the freezing. 



The next step toward the introduction of lard-oil was the devising of 

 a system by which it could be inspected, and the Board assured, before 

 it should be too late to remedy the evil, that the lard purchased was of 

 a good quality. This was a matter of great importance, and involved 

 no small degree of responsibility, since the contractor was entitled to 

 his pay immediately after the acceptance of the oil, and while the quan- 

 tity i^urchased amounted annually to nearly 100,000 gallons. 



The conclusion was arrived at that it was impossible, from any single 

 test that could be applied to small samples, to determine the quality of 

 the oil as applicable to light-house purposes; and that in the present 

 state of our knowledge as to its character the following tests are re- 

 quired to fully insure in all cases the required quality of the article : 



1 . Specific gravity at 60° F. 



2. Liquidity at different temperatures. 



