_OF MICROSCOPIC OBJECTS. 77 
is to be used in the approach of light to the inflammabie 
vapour. 
After the Foraminifera and calcareous forms have been 
removed, the residue may be treated with acids and leviga- 
tion in the usual manner, to obtain siliceous forms and 
discs, if there be any present; but to facilitate their 
deposition, and to avoid the loss of any minute atoms 
suspended in the washings, I would suggest the use of 
filtration. The conical filter is unsuitable, as the particles 
would spread over too great a surface of paper; but glass 
tubes open at both ends (such as broken test-tubes) will be 
found to answer, the broad end covered with filtering-paper 
and over that a slip of muslin tied on with a thread to 
facilitate the passage of the water and prevent tho risk of 
breaking the paper. Suspend the tube over a suitable 
vessel throngh a hole cut in thin wood or cardboard, pour 
in the washings, which can be thus filtered and then dried. 
The cloth must be carefully removed, the paper cut round 
the edges of the tube, and the diatoms on the paper disc 
may be removed by a camel-hair pencil or otherwise, ready 
for mounting. Thus many objects may be preserved which 
would be either washed away or only be obtained by a more 
tedious process. 
Such is Mr. Dale’s method of cleaning the soundings 
from tallow, and as it thoroughly accomplishes its end, and 
is alike effective and not injurious to Foraminifera and dia- 
toms, it may be safely recommended. The weak solution of 
caustic potash before advised for Foraminifera, must not be 
used where it is desired to preserve the diatoms, as they 
would certainly be injured, or cree altogether, if this 
agent were employed. 
In fixing the Foraminifera ion the slide, no better plan 
can be followed than the dry cells and gum recommended 
in the early parts of this chapter. Owing to their thickness 
and composition, most of them are opaque objects only ; but 
they are exquisitely beautiful, and require no particular care, 
except in allowing the cell to be perfectly dry when 
