(_a_) The temperature—whether summer or winter; (_b_) The freshness of the fish; (_c_) The quality of the salt—its purity and grain; (_d_) The quantity of salt used; (_e_) The duration of the process. (_a_) _The Temperature._ As soon as a fish is dead, it commences to decay. In hot weather, decay proceeds more rapidly and the interior portion of the meat may become soured before the salt reaches it. Clearly, if the rate at which the salt penetrates the fish is retarded by the salt being impure, or of too fine a grain, or by the brine being too weak, the probability of the fish being spoilt is very much increased. The dry salt method leads to a much quicker penetration of the fish than the brine method, and should always be used in warm weather. (_b_) _The Freshness of the Fish._ The decay processes gather impetus day by day. It is clear, therefore, that in order to avoid the possibility of “souring,” the fish should be salted with the least possible delay. (_c_) _The Quality of the Salt._ (1) _Its Purity._ The impurities commonly present in Fishery Salt are the sulphates and chlorides of calcium and magnesium. The following analysis show the composition of typical samples of Fishery Salt. -----------------------+--------+--------+--------+--------+-------- | German | | | | Composition. | Rock |Italian.|Spanish.|French. |English. | Salt. | | | | -----------------------+--------+--------+--------+--------+-------- | % | % | % | % | % Salt (Sodium chloride) | 97·28 | 96·59 | 96·63 | 95·86 | 98·9 | | | | | Calcium chloride | -- | 0·32 | -- | 0·16 | -- | | | | | Magnesium chloride | 0·25 | 1·19 | 0·96 | 0·35 | 0·08 | | | | | Magnesium sulphate | -- | 1·75 | 0·73 | -- | -- | | | | | Sodium sulphate | 0·44 | -- | -- | -- | 0·04 | | | | | Sodium bicarbonate | 0·01 | -- | -- | -- | -- | | | | | Insoluble (Calcium | | | | | sulphate, sand, etc.)| 2·02 | 0·15 | 1·68 | 3·63 | 0·98 -----------------------+--------+--------+--------+--------+-------- | 100·00 | 100·00 | 100·00 | 100·00 | 100·00 +--------+--------+--------+--------+-------- Moisture | 0·20 | 6·54 | 4·47 | 1·39 | 3·25 -----------------------+--------+--------+--------+--------+--------