1875] WRITINGS OF JOSEPH HENRY. 495 



If now the temperature rises, a small portion of the oil remains solid 

 until the temperature reaches 44-6°. 



Third experiment.— ThQ oils were placed in large cylinders and exposed 

 to a temperature of 24-8° F., with the following results: 



1. Crude lard oil, much sediment. 



2. Sperm oil, ditto. 



3. Pure refined lard oil, a little sediment. 



4. Winter-strained lard oil, very little sediment. 



5. Whale oil, no sediment. 



In the use of sperm oil, it was found that the purer it could 

 be obtained the better, and hence it was the custom to strain 

 the oil (and also the drippings) through clean white sand 

 previous to using it. In the case of lard oil however, (as 

 before stated,) it was found that removing all the solid 

 matter diminished its photometric power. 



All fatty oils absorb oxygen, which unites with them to 

 form oxides of their combustible ingredients; accordingly oil 

 freely exposed to the air must in time gradually diminish 

 in its power of combustion. It should therefore not be open 

 to the atmosphere when the oil is to be stored, but covered 

 with a thin wooden plane which floats upon the surface of 

 the oil and thus in a great measure excludes the air. The 

 freezing of lard oil does not appear to affect its quality. 



Considerable difficulty was experienced in the introduction 

 of lard oil on account of the objection to it on the part of the 

 keepers; in some cases from the want of experience in using 

 it, and in others from the interference of venders of sperm 

 oil. This difficulty however was obviated by a resolution 

 of the board, by which any keeper who declared his inabil- 

 ity to burn lard oil should be requested to resign, since it 

 had been abundantly proved that this oil with proper man- 

 agement could be made to compete favorably with sperm oil. 

 Its introduction was a matter of great importance in an 

 economical point of view; it saved the Government $100,000 

 annually for several years. 



Another important step in the introduction of lard oil was 

 that of furnishing a lamp which would burn it with the 

 greatest perfection. This was effected by the invention of Mr. 

 Joseph Funck, foreman of the lamp-shop. In order to burn 



