484 INVESTiaATIONS RELATIVE TO ILLUMINATING MATERIALS. 



United States Army. To this manufactory the Light-House Board gave 

 special encouragement, and purchased at a liberal price all the oil that 

 could be supplied; the quantity however which could be procured was 

 but a small part of the illuminating material required for the annual 

 consumption of the Light-House Establishment. 



The price of the sperm-oil still continuing to increase, the Board em- 

 ploj'ed Prof. J. H. Alexander, a chemist of Baltimore, to make a series 

 of investigations on different oils, to ascertain a method of detecting 

 ad alterations in them, and to determine the relative economical value 

 of different kinds of oil which might serve for use in light-houses. In 

 his report Mr. Alexander recommended, as a means of detecting adul- 

 terations in oil, a thermal test, which was based upon the amount of 

 heat evolved by mixing a given quantity of the oil with sulphuric acid 

 of a given specific gravity, and noting the rise of temperature as indi- 

 cated by a standard thermometer in a unit of time. For using this 

 method, it was pi^posed to ascertain by actual experiment the heat 

 evolved by mixing pure oils with a given quantity of acid, and afterward 

 oils adulterated with given quantities of lard or inferior oils. This in- 

 genious suggestion was however never reduced to practice. The method 

 was too refined; the difference of heat evolved was scarcely suificient 

 to be noted unless great j)recautions were taken to prevent loss by ra- 

 diation and conduction, and consequently it could not be employed by 

 ordinary inspectors. In regard to lard-oil, ^Ir. Alexander failed to em- 

 ploy the proper method of burning it, and consequently rated it very 

 low on the scale of economical value as a light-house illuminant. 



In this stage of the liistory of the subject we are presenting, the chair- 

 man of the committee on exi^eriments commenced himself to investigate 

 the qualities of different kinds of oil, and was soon led to direct his at- 

 tention to the comparative value of sperm and lard oils. The experi- 

 ments made by Mr. Alexander were with small lamps, and the compari- 

 son in this case, as will be shown, was much against the lard-oil. 



The first experiment of the new series consisted in charging two small 

 conical lamps of the'capacity of about a half-pint, one with pure sperm- 

 oil and the other with lard-oil. These lamps were of single-rope wi(;ks, 

 each containing the same number *of strands; they were lighted at the 

 same time, and the photometrical power ascertained by the method of 

 shadows. At first the two were nearly equal in brilliancy, but after 

 burning about three hours the flame of the lard had declined in photo- 

 metric i)ower to about one-fifth of that of the flame of the sperm. The 

 question then occurred as to the cause of this decline, and it was sug- 

 gested that it might be due — first, to a greater specific gravity in the 

 lard-oil, which would retard the ascent of it in the wick, after the level 

 of the oil had been reduced by burning in the lamp ; or, second, to a 

 want of a suflicient attraction between the oil and the wide to furnish 

 the requisite sujiply as the oil descended in the lamp; or, third, it might 



