Now, the reaction
NaC_2H_3O_2 + 3H_2O = NaC_2H_3O_2.3H_2O
(anhydrous acetate) (crystals)
evolves 4.37 calories (Berthelot), or 1.46 calorie for each molecule of
water; and whereas 1 kilo. of water only evolves 1 large calorie of heat
as its temperature falls 1 deg. C., 18 grammes of water (1 gramme-molecule)
evolve l.46 large calorie when they enter into combination with anhydrous
sodium acetate to assist in forming crystals--and this 1.46 calorie may
either be permitted to warm the mass of crystals, or made to do useful work
by raising the temperature of some adjacent substance. Sodium acetate
crystals dissolve in 3.9 parts by weight of water at 6 deg. C. (43 deg. F.)
or in 2.4 parts at 37 deg. C. (99 deg. F.). If, then, a jacket round an
acetylene apparatus is filled with a warm solution of sodium acetate
crystals in (say) 3 parts by weight of water, the liquid will crystallise
when it reaches some temperature between 99 deg. and 43 deg. F.; but when
the generator comes into action, the heat liberated will change the mass of
crystals into a liquid without raising its sensible temperature to
anything like the extent that would happen were the jacket full of simple
water.
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