In this case the hopper is supported by the main portion of the
apparatus, and does not move with the bell: the rod and valve being given
their motion in some fashion similar to that figured. Apparatus designed
in accordance with the sketch M, or with the modification just described,
are usually referred to under the name of "hopper" generators. On several
occasions trouble has arisen during their employment owing to the jamming
of the valve, a fragment of carbide rather larger than the rest of the
material lodging between the lips of the hopper and the edges of the
mushroom valve. This has been followed by a sudden descent of all the
carbide in the store into the water beneath, and the evolution of gas has
sometimes been too rapid to pass away at the necessary speed into the
holder. The trouble is rendered even more serious should the whole charge
of carbide fall at a time when, by neglect or otherwise, the body of the
generator contains much lime sludge, the decomposition then proceeding
under exceptionally bad circumstances, which lead to the production of an
excessively high temperature. Hopper generators are undoubtedly very
convenient for certain purposes, chiefly, perhaps, for the construction
of table-lamps and other small installations.
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