INVESTIGATIONS RELATIVE TO ILLUMINATING MATERIALS. 403 



be assured that full justice is doue him iu the examination. xVfter see- 

 ing- the iirecision with which the photometric and other processes are 

 conducted, he is generally fully satisfied as to the results obtained, even 

 though his oil may have been rejected. 



The oil is delivered in iron-bound casks, varying^ from 38 to 50 gal- 

 lons. These are placed, previous to insi)ection, under a shed and ar- 

 ranged iu different lots, each containing- oil of the same quality. From 

 different casks samples are taken in tin canisters of a capacity of about 

 half a gallon ; each canister being marked with the number of the lot 

 and the cask from which the oil was taken. Before the sample is drawn 

 from the cask the oil within is thoroughly mixed by rolling the cask, or 

 by stirring. The object of this is to obtain in the sample an average 

 amount of solid matter which may be contained in the oil. 



The purest lard-oil is that which is manufactured by submitting the 

 solid leaf lard to great pressure during- the coldest period of winter. 

 Oil of this quality is used for burning iu small mechanical lamps; it 

 gives a bright llame and does not incrust the wick. The light house 

 lamps however being of a much larger size and evolving a much 

 greater amount of heat, can consume oil of a coarser character; and 

 indeed it has been found that oil containing a certain amount of solid 

 matter, provided the latter is not too much in quantity to be consumed 

 by the lamp, gives a higher illuminating power. On this account, be- 

 fore this fact was generally known in the trade, complaints were made 

 of the Light- House Board giving the preference to oil which, in the 

 market, would not be considered of the first quality. 



The quantity of oil is estimated by weight, allowing 7.6 pounds per 

 gallon. It is weighed in gross and afterward emptied into large tanks 

 in an underground vault. The empty barrels are next weighed ; the 

 weight of these deducted gives the net weight of the oil. 



Previous to the establishment of the general lighthouse depot at 

 Staten Island, from which all the supplies are now distributed, and the 

 lamps and other lighthouse appliances are prepared for immediate use, 

 the oil was received at various ports along the coast, iu accordance 

 with terms of the contract, and was stored until wanted for use, in cel- 

 lars hired for that purpose. 



The Board however after the introduction of lard-oil, constructed 

 a spacious underground receptacle capable of containing 50,000 gallons 

 of oil, and retaining it during the whole year at a temperature not to 

 exceed 65° Fahrenheit. 



The underground vault contains five tanks, each of the capacity of 

 • ten thousand gallons. On each tank is a register, consisting of a glass 

 tube so divided as to give the contents in hundreds of gallons. The oil 

 is delivered in three installments : The first on the 1st of May, the sec- 

 ond on the 10th of June, and the third on the 22d of July. The vault 

 and tanks were constructed under the direction of General Poe while 

 engineer secretary of the board, who also took a lively interest in tbe 



