1) To approximately 100 pounds of salmon cannery waste in the 

 digester an equal weight of cold fresh water was added. 



2) The desired percentage of alkali (NaOH) by weight of salmon 

 waste used was dissolved in 1 to 2 gallons of fresh water 

 and added to the mixture in the digester. 1/ 



3) The stirring apparatus was turned on and steam added so that 

 the desired temperature was reached within 10 to 30 minutes. 



4) Heating was continued at the desired temperature or for the 

 prescribed length of time until a sample of the liquor showed 

 little if any solids remaining except bone particles, 



5) iVhen the digestion was complete the stirring apparatus and 

 steam were turned off. The mixture was allowed to stand for 

 1$ minutes to permit most of the bones and the remaining few 

 other solids to settle. 



6) 'Vhile the mixture in the digester was settling, the centrifuge 

 was started and preheated by passing about 10 gallons of hot 

 water (200°F. to 210°F.) through the machine. 



7) After settling for 15 minutes the bottom half of the liquor was 

 allowed to drain off as waste. The remaining liquors in the 

 digester were passed through the centrifuge. 



8) The oil recovered was weighed and the samples for vitamin A 

 analyses hermetically sealed in 1/2-pound flat cans. 



Variations in Procedure for Alkali Digestion 



Anderson (2) reported several variables he used in his laboratory 

 studies of the alkali digestion of saL-nbn heads and collars, Butler and 

 Miyauchi (1) mentioned a few of the variables but were unable to study 

 them thoroughly. The present studies carried out at the Fishery Prod- 

 ucts Laboratory, Ketchikan, Alaska, considered the four principal varia- 

 bles in the processing procedure: particle size, amount of alkali, 

 digestion temperatures, and digestion time. 



Amount of Alkali 



The first variation considered was the percentage of alkali used. 

 In all of the tests of this series the waste was ground through the Cali- 

 fornia Press Grinder and the temperature was kept constant at 200° p. The 



TJ The 1 to 2 gallons of water used for dissolving the alkali was part 

 of the equal weight of water used in part 1) 



101 



