128 American Fisheries Society 



By appropriate methods of measuring the rate of penetra- 

 tion of salt into fish it was found that if absolutely pure salt 

 is used, a very rapid penetration is obtained but even small 

 additions of from y^ to 5 per cent of these salts of calcium and 

 magnesium cause a very pronounced retardation of penetration. 

 In order to bring about a much more rapid penetration of the 

 tissues, then, we have but to obtain a salt free from these 

 impurities. The time gained by the use of pure salt enables fish 

 to be salted at a much higher temperature and yet not spoil. Fish 

 were salted in an incubator room in Washington last January 

 at a temperature of 90° F. at first, rising to 100° F. — the 

 hottest summer weather. No unpleasant odor developed, and the 

 fish, upon being cooked and eaten, were pronounced excellent. 



There was a further and somewhat unexpected difference 

 between the effects of pure and impure salts. The flesh of the 

 fish salted by impure salt is white, opaque, or chalky in appear- 

 ance, and much harder or firmer in consistency; that of fish 

 salted with pure salt is translucent and somewhat yellowish and 

 much softer. While the former white, firm, fish is the custom- 

 ary quality demanded in commerce, there are strong reasons for 

 believing the softer and yellowish fish produced in pure salt to 

 be superior. There is reason for believing that the whitening 

 of the fish in impure salt is explained by the fact that the calcium 

 coagulates the protein, just as heat, by coagulating egg white, 

 causes it to be white and firm. But where there is no calcium in 

 the salt, the protein retains its natural translucency and yellow- 

 ish color. The calcium in impure salt is retained by the fish, a 

 matter that will be discussed later under the subdivision on 

 flavor of salted fish. 



At this point, mention should be made of another effect of 

 salt upon the protein constituents of fish. Strong solutions of 

 salt precipitate certain protein substances, different substances 

 falling out successively from a mixture of dissolved proteins as 

 the concentration of salt is increased. The nature of the pro- 

 teins is not altered by this precipitation, for upon replacement of 

 the salt solution with fresh water the proteins redissolve and 



