by practical experience and by experiment that at a sufficiently elevated 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. Working at a lower temperature is the only practicable means of retarding decomposition, 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 rapidly?
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:
| Substances present. | Turks Island salt. |
Trapani, Italian salt. |
Iviza, Spanish salt. |
Diamond Flake, domestic salt. |
Leslie Velvet Grain, California salt. |
| Per cent. | Per cent. | Per cent. | Per cent. | Per cent. | |
| Sodium chloride | 96.52 | 95.82 | 98.05 | 99.78 | 99.96 |
| Calcium chloride | .32 | .49 | |||
| Calcium sulphate | 1.53 | .37 | .067 | ||
| Magnesium chloride | 1.20 | 1.19 | .00 | .00 | |
| Magnesium sulphate | .80 | 1.75 | .80 | .00 | .010 |
| Sand, etc. | .13 | .15 | .06 | .00 | .022 |
↑ These figures represent analysis of single samples of each brand taken in the market and are not averages 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 12 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 penetrated as deeply in less than five and one-half days as did salt containing 1 per cent calcium chloride in nearly seven days. Similarly, a salt containing 4.7 per cent magnesium chloride penetrated no farther 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 Washington 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-
