BY II \M M.ToV tl. SM ITU. 51 



never be recognized as the same gathering. Supposing now i 

 trial shows us the diatoms tolerably abundant, the trial being 

 made by heating in the manner presently to be described; the 

 phial is filled with alcohol and water, half and half. Borne 



samples of alcohol leave behind a scum after evaporation, 

 especially noticeable after burning in the mode presently to be 

 described, and water which will leave crystals, or any scum, 

 must be avoided; the beauty of the preparation will largely de- 

 pend upon being particular in this matter. 



For mounting diatoms I invariably place a drop of the fluid 

 containing them upon the cover, fievev on the slide. The alcohol 

 and water will spread out on the slide, but will remain heap <1 

 upon the round cover, like a plane convex lens. I prepare a 

 little stand, represented in the accompanying wood cut, of 

 quite fine wire (so as not to conduct off too much heat) bent at 

 right angles and inserted into a base; the free end is bent into 

 a ring, and upon this ring is placed a square 

 plate of very thin iron, (such as is used for the 

 so-called " tintypes" in photography, with the 

 Japan burned off,) held in place by bending 

 the corners of the square over the ring, loosely, 

 to allow expansion, without bending when 

 heated; upon this plate the cleaned cover is 

 placed, and then, by means of a pipette, a drop 

 of the alcoholic liquid with the diatoms is 

 placed upon it, and the spirit lamp applied below. The alcohol 

 takes fire and is allowed to burn out; the flame of the lam}) is 

 then placed beneath, and the rest gently boiled, the remaining 

 alcohol escaping during this ebullition causes the diatoms, by 

 this very act, to distribute themselves wry evenly over the 

 cover, and all matting is effectually prevented. It is better 

 after one perceives that this even distribution has taken place, 

 not to push the heat so as to make large bubbles again, but to 



slowly evaporate until dry, after which the full power of the 

 Ham.' must he applied until the iron plate and the glass OOVeZ i^> 

 red hot; at first the ma8S of diatoms, etc.. will become black, 

 but as the organic contents and <l< J >ris burn away there will 

 finally remain only the 8ileX nearly white. I invariably burn 

 in this manner on the cover even the specimens which have 



