228 How to jpre^are Sjoecimens of Diaiomacem for 



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 completely. 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 ofl' 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 examina- 

 tion 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 specimens may be obtained ; but such would not, 

 or, at all events, should not, satisfy the student of the Diatomaceae. 

 For him more elaborate methods are 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. Eunning 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 are to be used to hold the vessels in which 

 the specimens are to be manipulated over the source of heat used. 

 Mr. C. (Jr. Bush, late of Boston, Mass., who has had considerable 

 experience in cleaning Diatomaceae, tells me that he uses a lamp 

 burning petroleum oil, as cheaper than a spirit lamp, and, to 

 support the vessels he employs, has a little metal arrangement on 

 the top of the chimney, such as is supplied for the purpose of 

 holding a small tea-kettle and the like. The only objection to the 

 oil lamp is, that, unless the wick be well turned down, we are liable 

 to have our vessels blackened. However, the heat given off by burn- 

 ing petroleum is very great, and I have often used such a lamp 

 with advantage. If desired, of course, the source of heat used may 

 be gas, burned in a Bunsen's burner, or a spirit lamp ; and this 

 last, especially if it be sujoplied with a metal chimney to cut off 

 draughts, is, all things considered, the best, as it is very cleanly, not 

 being liable to smoke the bottom of the glass or porcelain vessels 

 used. If we are going to work with large quantities of material, 

 we shall require a small sand-bath to heat the glass vessels upon. 

 In small quantities, the diatoms may be boiled in test-tubes, when 

 some sort of holder will be required. The metal ones, sold by 



