Discussion of Results 



The numerical data obtained in the thirty-two trial alkali diges- 

 tions of whole pink salmon waste are summarized in Table 1. The data 

 exhibit no clear-cut advantage for any one of the digestion procedures 

 tried. Therefore it is necessary to rely considerably on the visual 

 observations which are not easily recorded in a table. Notes were 

 kept on the following pertinent factors: rate of digestion of the 

 fleshy parts, the formation of soap and foam, the occurrence of diffi- 

 cult emulsions, and the appearance of the separated oil and of the dis- 

 carded mixture. 



Effect of Particle Size 



The lack of or the degree of grinding of the salmon cannery waste 

 prior to digestion has a noticeable effect on the time required for com- 

 pleting the digestion. However, the data shows no correlation between 

 the particle size of the raw material and the oil or vitamin A recovery. 

 Since variation between duplicate experinents was quite high, any small 

 apparent differences in oil yield or vitajnin content are probably of no 

 significance. Coarse grinding of the cannery waste reduces the diges- 

 tion time sufficiently so as to warrant inclusion of this step in any 

 recommended procedure. 



Amount of Alkali 



'.Vhen only 1 percent sodium hydroxide by weight of the waste was 

 used, the total digestion time was excessive; even after 90 minutes a 

 large share of the oil had not yet been released. Using between 1-1/2 

 and 3 percent alkali the digestions proceeded satisfactorily. In the 

 tests where 4 to 5 percent alkali were employed excessive amounts of 

 soap were formed and emulsions hindered efficient separation of the oil. 

 As 1-1/2 percent alkali gave satisfactory digestions and good oil yield, 

 increasing the quantity of alkali, and thus the operating costs, seems 

 to be without advantage. 



Temperature of Digestion 



In the range between 190° sind 210° F. the temperatures of the diges- 

 tion seem to have little effect on the oil or vitamin yields. At 210° F. 

 the incoming steam caused violent agitation of the mixture; there was a 

 tendency toward foaming and some of the mixture was lost from the retort. 

 Digestion at 2C0° F. proceeded nearly as rapidly as at 210° F. and the 

 temperature was easier to control. Because there is no saving in time 

 the lower digestion temperature would use steam more economically. Diges- 

 tion at 190° F. was equally esisy to control, probably just as economical, 

 but required slightly more time for completion. 



106 



