6 



U. S. BUREAU OF FISHERIES. 



by practical experience and by experiment that at a sufficiently ele- 

 vated temperature the fish will invariably spoil if blood be present. 

 Now, to make certain that the race mentioned shall always be won 

 by the salt, we may do one of two things, namely, retard the rate of 

 decomposition or accelerate the penetration of salt. Worldng at a 

 lower temperature is the only practicable means of retarding de- 

 composition, but since we desire a method suitable for warm climates 

 it is necessary to accelerate penetration of salt. How can the salt be 

 caused to penetrate fish more rapidlj' ? 



The physiologists have shown that in living animals compounds of 

 calcium, barium, and magnesium have a marked effect in retarding or 

 arresting penetration of membranes. By examination of numerous 

 analyses of commercial brands of salt it was found that the salts of 

 calcium and magnesium are those nearly always present as impurities. 

 A few of these analyses are given herewith : 



Analysis of Various Salts fob Curing Fish.' 



Substances present. 



Turks 

 Island 



salt. 



Trapani, 



Italian 



salt. 



Iviza, 



Spanish 



salt. 



Diamond 



Flake, 

 domestic 



salt. 



Leslie 

 Velvet 



Grain, 

 Califor- 

 nia salt. 



Sodium chloride 



Calcium chloride 



Calcium sulphate 



Magnesium chloride . 

 Magnesium sulphate. 

 Sand, etc 



Per cent. 

 96.52 



Per cent. 



95.82 



.32 



Per cent. 



98.05 



.49 



Per cent. 

 99.78 



Per cent. 

 99.96 



1.53 

 1.20 



.13 



1.19 



1.75 



.15 



.067 

 .00 

 .010 

 .022 



1 These figures represent analysis of single samples of each brand taken in the market and are not aver- 

 ages of numerous samples. Not only is some variation in manufacture unavoidable, but the chemical 

 determination of such small quantities of impurities is subject to small errors. Therefore it should not be 

 expected that any purchased lot of salt would conform exactly to the composition shown here. The 

 figures represent in a general way the degree of purity that can be expected. 



By appropriate methods of measuring the rate of penetration of 

 salt into fish it was found that if absolutely pure salt is used a very 

 rapid penetration is obtained, but that even small additions (from 

 I to 5 per cent) of these salts of calcium and magnesium cause 

 a very pronounced retardation of penetration. For example, by 

 appropriate methods of analysis it was found that pure salt pene- 

 trated as deeply in less than five and one-half days as did salt con- 

 taining 1 per cent calcium chloride in nearly seven days. Similarly, 

 a salt containing 4.7 per cent magnesium chloride penetrated no far- 

 ther in five days than pure salt did in three. 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 Wash- 

 ington 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 appearance 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 customary quality demanded in com- 



