20 FORAMINIFERA 



Washing. For the examination of the foraminifera, clean 

 tests are necessary. In order to get these, the dredged material 

 which contains mud and fine sand, should be washed. This is 

 best done by means of nested sieves, such as are obtainable at 

 most laboratory supply houses. Brass sieves with meshes of 

 200, 120, 80, 40, etc., to the inch can be obtained. For more 

 practical purposes sieves with 40-, 80-, and 200-mesh to the 

 inch are sufficient. The mud is placed directly in the top sieve, 

 and a stream of water with a fine spray played upon the ma- 

 terial. If the sieves are shaken so that the material is kept in 

 motion, the finer particles will be washed through readily. The 

 resulting clean foraminifera can then be dried. It is sometimes 

 more satisfactory to wash material through the coarsest sieve 

 first into some sort of retainer, and then this again passed 

 through the finer sieves. By this means the finer meshed sieves 

 do not clog with the material. If sufficient water is used con- 

 stantly, the tests will be in practical suspension and will not be 

 damaged even with a rather strong current of water. With 

 very delicate material, it is sometimes best to wash the material 

 in muslin bags simply agitating the bag in a container of water 

 until all fine mud is washed away. Material may be dried in 

 the open air or if speed is necessary by artificial means, either 

 a hot plate or on some sort of stove. With very delicate ma- 

 terial, it is often best not to dry the sample too quickly or to 

 have it get too hot in the process. 



Sorting. After the material is washed it often helps in the 

 examination if preliminary sorting can be done. There are dif- 

 ferent methods of doing this. One is that called ''spinning". By 

 this method, the material is put with clean water in a plate or 

 watch glass or in any dish with water so that a circular motion 

 can be set up. This is the old method by which gold was 

 "panned" by the miners. The gold dust was heavier than the 

 sand and came to the middle of the pan. In the case of the 

 foraminifera, however, they being lighter material than the sand, 

 accumulate on the outer edges. This can be washed off in the 

 process into a larger receptacle below. 



Another method by which rough sorting can be done is by 

 "decanting". If the material is shaken up in a tall vessel of 

 some sort, the lighter specimens will stay in suspension for a 

 short period and can be poured off, leaving the heavier ones on 



