62 THE AMEEICAN MONTHLY [March, 



gently slid under the edge of the raft, which will then float into the 

 deeper end, thence transfer it to a collecting bottle, and label it with 

 the locality in which the collection was made. Such an instrument 

 will also be found of great use in skimming the surface of mud where 

 diatoms are suspected. Having made the collection, one of the most 

 troublesome operations is that of freeing the diatoms from impurities. 

 If they adhere to fresh-water plants or to marine alga, and are free 

 from mud, rinsing them oft' in water, to which a small quantity of hy- 

 drochloric or acetic acid has been added, will detach them in a toler- 

 ably clean condition; but where they ai^e mixed with mud and other 

 contaminations nothing but repeated washings and decantings will sep- 

 arate them. Dr. H. Munro says : " I first boil the deposit in strong 

 hydrochloric acid for five or ten minutes, allow it to subside, pour oft' 

 all the acid, and by a few washings get as much of it away as possible. 

 Then treat in the same way with sti'ong nitric acid, washing the de- 

 posit repeatedy to get rid of the remaining acid. When this is done, I 

 then separate the diatoms, according to their difterent gravities, by al- 

 lowing them to pass through a column of water in the following man- 

 ner : I take a long glass-tube, about four feet long and half-an-inch 

 bore. At the bottom of this tube is fixed a stop-cock, to enable me to 

 let out any of the diatoms during any stage of the process. Having 

 nearly filled this tube with distilled water I pour in my deposits washed 

 free from the acids. I watch the deposit as it falls slowly and gradually 

 down the tube. In about a quarter of an hour many of the larger forms 

 will have descended to the bottom of the tube. By turning the tap at 

 the bottom of the tube I let out a drop of the mixture on a slide ;" and 

 so he proceeds, waiting a longer interval between each turning of the 

 tap to allow of the lighter forms settling. In this manner they are tol- 

 erably well sorted into sizes. The only weak point about this plan is 

 that it merely separates bodies of the same specific gravity, so that for- 

 eign matter is not eliminated, but sinks with the diatoms. The larger 

 specimens which descend with the grains of sand in the first fall may 

 be easily picked out. 



Prof. Bailey, in Silliman's Journal, recommends the following: 

 " Dissolve out the lime compounds if present by means of nitric acid 

 or hydrocloric acid, then wash and filter ; put the moist contents of the 

 filter into a' porcelain capsule, with enough strong sulphuric acid to 

 make the whole a fluid mass. Heat the capsule over a spirit lamp until 

 the organic matters are all charred, and continue the heat until strong 

 acid fumes are evolved. Keep the capsule hot, and, in minute portions 

 at a time, add finely-powdered chlorate of potash. If the acid is hot 

 enough to give oft' fumes, the chlorate will be immediately decomposed 

 without the accumulation of explosive gases, and it will exert so pow- 

 erful an oxidizing action that in a few moments a carbonaceous mate- 

 rial as black as ink will become clean and colorless. Nothing will now 

 remain to be done but to wash oft' the acid, which is best done by the 

 addition of water and repeated decantations. I would advise that the 

 material thus cleaned should not be dried, but should be kept in bot- 

 tles with a little alcohol, which prevents felting together, and does not 

 allow of the byssoid plants which often develop in water. It is neces- 

 sary to caution those not familiar with chemistry against using the chlo- 

 rate of potash with sulphuric acid in any other way than that above 



