The perfectly dried matter is best treated in exactly the same way as a
residuum in water analysis. It is a common thing to ignite the residuum,
and to put the loss down, if any, to water. This ought not to satisfy an
accurate observer, since organic matter, carbonates--especially in
presence of silica--will easily add to the loss. The best plan is to
heat a small portion very cautiously, and note if any smell or
alteration in color, due to carbon, etc., is perceptible, and to proceed
accordingly.
I have seen some very satisfactory analyses made on board ship by a
skillful use of the blowpipe, where liquid reagents would be very
inconvenient to employ.
It will be necessary to say a few words as to the way in which
soundings are made at sea. When the bottom consists of sand, mud, or
other loose matter, it is easy enough to bring specimens to the
surface, and, of course, we know in such a case that the bottom has
been reached, but, in the event of the bottom being hard and rocky, it
is not easy to say that our sounding has been successful: and here we
meet with a difficulty which unfortunately is most unsatisfactorily
provided for.
The lead is "cast," as the saying goes, "armed" for this emergency. An
iron sinker is made with a hollow recess in the bottom; this is filled
in with tallow, and on striking the bottom any loose matter may adhere
by being pressed into the tallow.
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