NATURAL HISTORY OF THE DIATOMACE.E. 489 



them arc to be found the delicate Coscinodiscus subtilis, Eupodiscus 



argus, and Triceratium favus. Both of these two last named forms occur 

 commonly on our Atlantic coast, and muds from Charleston, S. C, and 

 Wilmington, Ga., have provided me with them in plenty. Cargoes of 

 bones, which present green incrustations from having lain in the water 

 for some time, are said to yield diatoms, some of which may be rare, as 

 coming from foreign ports. The state of New Hampshire has not yet 

 been sufficiently gone over for it to be said what the characteristic forms 

 of diatomacca: growing within its boundaries are, but yet we may safely 

 predict that the lakes, ponds, streams, and sea-coast of that state will 

 yield to the searcher ample material of beautiful forms. 



If the microscopist wishes to mount a few slides of recent diatoms 

 just to show what diatoms are, nothing is easier. It is only necessary to 

 boil a small mass of them in strong nitric acid in a test tube over a spirit 

 lamp, and, when the acid has ceased to emit red or yellowish fumes, 

 wash them thoroughly with clean water, allowing them to settle com- 

 pletely. Then a little of the clean sediment, consisting almost entirely 

 of the shells of the diatoms, is taken up by means of a "dip-tube," and 

 placed upon the central portion of a glass slide. Here it is dried, and the 

 slide warmed over a lamp; then a drop of Canada balsam is permitted to 

 fall upon the diatoms. As soon as all bubbles have cleared off from the 

 balsam, a warm cover of thin glass is carefully laid upon it and permitted 

 to settle into place. When cool, it is ready for examination by means of 

 the microscope, any balsam which has exuded around the cover being- 

 washed off with alcohol. In this way rough and tolerably clean speci- 

 mens may be obtained ; but such would not, or, at all events, should not, 

 satisfy the student of the diatomacex. For him more elaborate methods 

 arc necessary, and these we will now proceed to consider. 



Apparatus and chemicals necessary. A chemist's retort-stand, which 

 is a heavy iron plate with an upright rod projecting from one side of it. 

 Running on this rod, and so arranged that they may be fixed by set- 

 screws at any height, are a series of rings of various diameters, which 

 arc to be used to hold the vessels in which the specimens are to be 

 manipulated over the source of heat used. Mr. C. G. Bush, late of Bos- 

 ton, Mass., who has had considerable experience in cleaning diatomacca:, 

 tells me that he uses a lamp burning petroleum oil, as cheaper than a 

 vol. t. 64 



