THE SALTING OF FISH. 21 



These analyses are given in order to show the large amounts of 

 impurities contained in some salts and to point out that it is possible 

 to purchase on the market salts that are very nearly pure. It is to 

 be noted that the chief impurities are calcium, magnesium, and sul- 

 phates. It is not known in just what chemical combination these 

 occur in the salt, but this makes no difference. The analyses are given 

 on a moisture-free basis in order that they shall be relative to each 

 other. Further, the amount of moisture contained in salt is of little 

 importance to the fish Salter; except that, of course, damp salt con- 

 tains less salt per ton than dry salt and, therefore, is more expensive 

 if it is purchased at the same price. 



INFLUENCE OF IMPURITIES ON RATE OF PENETRATION OF SALT. 



INTRODTTCTION. 



Former work on rate of penetration, — Bitting (1911), of the 

 Bureau of Chemistry, tried some experiments to show the effect of 

 fineness of salt upon the rate of penetration of salt into codfish. 

 Bitting's data show that in various coarse and fine salts there was 

 little difference in the rate of extraction of water from the tissues 

 or in the rate of penetration of salt into the fish. However, in his 

 work no consideration was given the chemical composition of the 

 salt. To make the work comparative, a single salt ground to dif- 

 ferent degrees of fineness would have to be used in salting all of the 

 experimental lots of fish. Bitting used various domestic and for- 

 eign salts which were of different degrees of fineness, but which 

 varied widely in chemical composition. It is stated tliat the cod 

 used were small in size, but no information was given regarding 

 the uniformity of size, which is a very important factor, as salt 

 will penetrate to the center of a thick fish much less readily than 

 it will penetrate a thinner fish. Nor does Bitting give any informa- 

 tion as to his method of obtaining a 50-gram sample from a fish. 

 Before the experiments could be repeated the exact size of the fish 

 used would have to be laiown and also the exact method of sampling. 

 The writer doubts that any method of sampling a fish other than 

 sampling a section of given thickness a definite distance from the 

 skin or flesh side of the fish would be accurate enough to show dif- 

 ferences in the penetrating powders of different salts. 



Im.portaince of rate of penetration. — A consideration of the cause 

 of souring had suggested that the souring is a decomposition of the 

 inner meat of the fish before the brine strikes through and stops the 

 decay. Various writers had observed an antagonism between the 

 bivalent metals and monovalent metals in their passage through 

 membrane. This suggested that the small amounts of calcium and 

 magnesium, which exist in commercial salt as impurities, might exert 

 a pronounced retardation on the penetration of the sodium chloride 

 into the fish. An attempt was, therefore, made to measure the in- 

 fluence of these metals on the penetration of the sodium chloride into 

 fish. If it were found that these impurities in salt caused the salt to 

 penetrate more slowly, then the use of purer salt would lessen the 

 danger of spoilage, for the fish would strike through more rapidly 

 and less time would be allowed for decay of the inner portion. 



