4 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 60. 



dredge should be dumped into a pail, about a pint of water added, 

 and the whole violently stirred with a stick. After the stirring and 

 as soon as the sand is thought to have settled, perhaps 30 seconds, 

 the muddy water is poured into a battery jar, another pint of water 

 is added and the process repeated. This washes the diatoms out of 

 the heavy sand and concentrates the material. Formalin is now 

 added to the jar, as previously directed, and after the material has 

 thoroughly settled the water is carefully poured away and the sedi- 

 ment is bottled. 



These two kinds of bottom samples are to be treated differently 

 at the laboratory. The muddy material is separated as far as possi- 

 ble by decantation from its clay and other very fine material in the 

 gathering. Muddy gatherings are also liable to contain particles 

 of decayed sticks, leaves, etc., which would be difficult to destroy by 

 acids and should first be removed by means of a piece of wire gauze, 

 having a mesh of perhaps about one-half mm. By pouring the 

 muddy gathering, well diluted with water, through this gauze, these 

 larger particles will be removed and the process of cleaning now to 

 be described will be rendered much easier. A small amount of the 

 mud is placed in a battery jar, about 50 cc. to a jar holding a liter, 

 and water added. It is best to add the water from the faucet with 

 a powerful stream, so as to mix up the contents thoroughly, or the 

 whole may be stirred with a rod or stick. ^Vhen such a jar has stood 

 for 45 minutes, the muddy water is poured away, fresh water is 

 added, and the process is repeated until the water after 45 minutes 

 is almost clear. From this point the samples from sandy and from 

 muddy bottoms are treated the same way. The water is poured off 

 and the material transferred to a beaker and about ten times its vol- 

 ume of commercial hydrochloric acid is added. This is to partially 

 bring into solution the organic matter, but especially to remove all 

 lime, such as shells, corals, etc. The material is boiled in the acid 

 for about 20 minutes. The acid is then poured away, after the con- 

 tents have thoroughly settled, fresh acid is added and again brought 

 to a boil. Commercial nitric acid is now added to the boiling beaker, 

 drop b}'' drop, care being taken that the contents do not foam up 

 over the beaker. This adding of the nitric acid to the boiling solu- 

 tion brings about the rapid oxidation of the organic matter in the 

 sample and leaves as a residue only the diatoms, such sand as is pres- 

 ent, sponge spicules, and other bodies composed of silica. The add- 

 ing of nitric acid should be continued until the red fumes of nitrous 

 acid produced by the oxidation process are no longer given off. The 

 beaker is now filled with water and the sediment washed free of 

 acids by repeated additions of water and decantation after settling. 

 The material is now examined under the microscope, and in most 

 cases it will be found to be clean, the diatoms present being bril- 



