AQUATIC I'KUUUOTS IN AKTS AND INDUSTRIES. 223 



item of great importance in the preparation of medicinal oil, and on 

 it is dependent in a large measure the quality of the product. In order 

 to get tlie largest possible amount of oil, some producers cook the 

 material entirely too long, notwithstanding that beyond a certain 

 [)oint anything gained in quantity is at great sacrifice of quality. In 

 pi-oducing a choice grade of oil, the livers must not be exposed to heat 

 any longer than absolutely necessary. 



The longei" the cooking is continued, the greater the quantity of 

 acids and decomposed albumen extracted from the hepatic tissues. 

 These substances render the oil strong and unpalatable, and detract 

 from its appearance. Further, the longer the livers are exposed to 

 heat, the more oxygenized the oil becomes, making it irritative to the 

 stomach and causing disagreeable eructations. For the production 

 of llie clearest and lightest medicinal oil, the livers should not be 

 exposed to a greater heat than 100° F., and that only for about 45 

 minutes. This, however, is not feasible because the quantity of 

 oil produced in that case would be too small to make the business 

 profitable. The time must, therefore, be extended as far as practi- 

 cable without detracting too much from the quality. But in order to 

 produce a first-class medicinal oil, the length of the cooking should 

 on no account exceed 2-^ov 3 hours, provided the capacity of the liver- 

 receptacle does not exceed 50 gallons. 



On completion of the cooking process, the mass of livers and oil is 

 allowed to cool. The oil rises to the surface and is drawn off and 

 filtered. The liver magma is subjected to pressure and yields a quan- 

 tity of dark oil suitable only for curriers' use. The residuary mass 

 of hepatic tissues is dried and used for fertilizing purposes. Its 

 market value in Gloucester and Boston was formerly $6 or $8 per ton, 

 but at present it is only about $3 per ton. 



Filtering the medicinal oil is accomplished by running it through a 

 box fitted with several straining frames covered Avith cloth of suc- 

 cessive degrees of fineness and with a tap at the bottom through which 

 the oil can be drawn. Or the filter may consist of one or two light 

 canvas bags fitted inside of a white moleskin bag with the smooth 

 side out. But in filtering the dai-k oil, it is better to run it through 

 charcoal. 



In the process of refining, the medicinal oil is placed in small recei)- 

 tacles, as 5-gallon cans, and refrigerated either naturally in cold 

 weather or by means of ice and salt, as already described in the pro- 

 cess of refining sperm oil. When thoroughly chilled and granulated 

 the congealed oil is compressed through cotton or canvas bags holding 

 about 4 gallons each, for the j)urpose of extracting the foots, wliite 

 pressings, or stearin. Two or three bags are i^laced regulai"ly 

 upon a substantial wooden platform or table provided with grooves 

 for conducting the outflowing oil to a receiving tank. On this i-ow 

 of bags there is laid a thin iron plate or slab, then another layer of 



