The drying of the cod and cuttlefish by the heated wind has been studied as a problem in physics. The results obtained by the present author are summarized as follows:
1) When the fish muscle is exposed to the air for a sufficiently long time at the room temperature, the amount of the water loss of the muscle is always constant, namely 79% of the initial weight for the cod and 73% for the cuttlefish, irrespective of the relative humidity of the air, if it is less than 60%. They are about the same value as those initial water content which were obtained by the chemical method using toluen.
2) A very complicated relation exists between the amount of water remained in the fish muscle and the time required for its drying. But it can be assumed approximately, that until the water decreases to the half of the initial quantity, the relation is represented by the fol-lowing equations derived by Dr. F
UJIWHARA and Dr. T
AUTI:-
∂
ρ/∂
t=KΔ
p, K(∂
ρ/∂
N)
s=
γEρs and
E=
F'-
f,
where
ρ is, the water density in the fish muscle at time
t,
S the suffix referred to the surface layer of the fish mucle,
N the inward normal at the surface,
F' the maximum vapour tension of the aqueous solution in the surface layer at the temperature of it,
f the vapour tension of the water contained in the wind,
K the coefficient of diffusion of the water in the fish muscle, γ the coefficient referred toevaporation of the water at the surface of the muscle.
K is esti-mated at about 0.01-0.03 cm
2/hr. and γ 0.005 when
E is measured in mm/Hg.
3) The upper limit of the temperature to which the above equation of diffusion can be applied is about 40°C, and the lower limit of the humidity is about 40% in the case of the temperature 30°C. Above 40°C, a peculier condition which accelerates the velocity of drying seems to occur in the fish muscle, and below 40%, a condition which decreases the velocity of drying seems to appear in the surface layer of the fish muscle, in the advanced stage of drying. Even if the temperature and humidity are within the above-mentioned ranges, the velocity of drying gradually increases when the water is evaporated more than half of the initial quantity.
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