Of MICROSCOPIC OBJECTS. 77 



is to be used in the approach of light to the inflammable 

 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 

 nitration. 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 the 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 maybe 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 destroyed altogether, if this 

 agent were employed. 



In fixing the Foraminifera upon 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 



