22 J. M. Blake — Improved Method of Cleaning Diatoms. 



when not in use, to avoid injury to the wood-section from 

 contraction. 



After the section has been in use for a considerable time 

 the pores gradually become stopped with fine sand. Clay 

 alone does not cause this condition. The only remedy is to 

 cement on a new section. 



An interesting point in this connection is that when we 

 burn an old strainer-section for the purpose of studying this 

 clogged condition, we find that the ash will crumble if damp- 

 ened, and will fall into numerous " sticks," each the length and 

 diameter of a pore of the wood, and each of these "sticks" 

 will be found to be packed with the small sand grains. 



It may be said in regard to the selection of wood, that white 

 pine — Pinus strobus — is excellent for ordinary use, since the 

 strainers cut therefrom work freely, Certain light diatoms 

 that would as a rule have been floated away in the usual set- 

 tling and pouring-off process, are here retained by the pine 

 section, because their length enables them to bridge across the 

 pores. Some very short forms, however, will pass through to 

 a considerable extent. 



By saving the tailings from the pine and passing them 

 through a spruce strainer, the majority of these short forms 

 were retained. The spruce here referred to was a piece of 

 flooring, and of a very white species of spruce. It was not 

 identified. There are several other species that would prob- 

 ably answer equally well. In using spruce, the sections should 

 be thin. The clay will be found to pass through the pores of 

 spruce with some freedom, but not so rapidly as through pine. 



There are some gatherings that will require a strainer of 

 still finer grain. This may be said of the very smallest diatoms 

 that grow on water plants. The majority of these may be 

 retained by a quite thin section cut from the white outer wood 

 of the red cedar Juniperus Virginiana. In one experiment 

 some of these very minute forms which had passed through 

 the spruce were almost wholly retained by the red cedar. 



It follows that from these three species of wood we can 

 obtain a graded series of strainers, each capable of separating 

 the clay from the diatoms, and at the same time furnishing a 

 ready means of grading as regards size. 



The pine strainer works the most rapidly and makes a very 

 good separation, and will meet ordinary requirements. The 

 spruce strainer can follow if we want a more thorough glean- 

 ing of the smaller forms ; and then we have the red cedar 

 section as a final resort to aid in securing the very smallest 

 diatoms. 



