The joint between the copper wire and the
zinc or aluminium plate should naturally be above the water-level. The
foregoing remarks should be read in conjunction with what was said in
Chapter II., about the undesirability of employing a soft solder
containing lead in the construction of an acetylene generator. Here it is
proposed intentionally to set up a galvanic couple to prevent corrosion;
there, with the same object in view, the avoidances of galvanic action is
counselled. The reason for this difference is self-evident; here a
foreign metal is brought into electrical contact with the apparatus in
order that the latter may be made electro-negative; but when a joint is
soldered with lead, the metal of the generator is unintentionally made
electro-positive. Here the plant is protected by the preferential
corrosion of a cheap and renewable rod; in the former case the plant is
encouraged to rust by the unnecessary presence of an improperly selected
metal.
OTHER ITEMS IN GENERATING PLANT.--It has been explained in Chapter II.
that the reaction between calcium carbide and water is very tumultuous in
character, and that it occurs with great rapidity. Clearly, therefore,
the gas comes away from the generator in rushes, passing into the next
item of the plant at great speed for a time, and then ceasing altogether.
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