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



An ordinary, well-known method of separation is to digest 

 the material with an acid, and then to dilute with water, and 

 allow the heavier portions to deposit. After an interval, the 

 lighter portions are poured away, and the process repeated 

 until the clay, very fine sand and broken diatoms have been 

 removed, while those diatoms which have not been floated 

 away during the process, remain with the coarse sand. This 

 process takes up considerable time, and requires careful atten- 

 tion and timing to decant successfully, and, in spite of this 

 care, some of the smallest and lightest forms can hardly fail to 

 be lost. 



The method now to be described was originated by the 

 writer some twenty years ago, and recently, in recurring to the 

 subject, it seemed that even at this date the method might 

 appear novel, since it has not been exhibited during the inter- 

 val, and no mention of a similar plan has been noticed in any 

 published directions for treating diatoms. Therefore, the way 

 seems open for a revival of interest in the subject, and this 

 method by which, for instance, a small test sample of diatoms 

 can be cleaned in five minutes' time from the acid-prepared 

 material, should appeal to novices as well as experts, by reason 

 of its saving of both time and effort. 



The first attempt to supplant the ordinary method of separa- 

 tion and cleaning was made by using a cloth sieve made of 

 partly worn cotton cloth stretched on a frame. The diatom 

 material was treated in the usual way, in a separate vessel with 

 acid. Then, when it had been largely diluted with water, the 

 mass was placed in this cloth-bottomed tray, and agitated and 

 jarred to carry off the clay through the cloth. More water was 

 then added, and the process repeated until only sand and 

 diatoms remained. This plan was not wholly satisfactory, 

 since a large proportion of the diatoms passed through the 

 cloth ; yet a considerable bulk of partly cleaned diatoms was 

 obtained, and by careful straining through a sieve the largest 

 diatoms were separated from the smaller and the broken forms, 

 and in this way were secured entirely free from debris. There 

 was an abundance of this material for distribution. 



Yery soon after this first experiment, the writer originated 

 an improved and more practical method which depended for 

 its success upon the use of cross-sections of wood. Coniferous 

 wood is the most suitable, since it has pores of nearly uniform 

 size, whereas other kinds of wood nearly always have large and 

 small pores commingled, which make them entirely unsuited 

 for the purpose. These wood cross-sections bear dilute acid 

 without injury, which would not be the case with a metal 

 strainer of equally fine mesh, even supposing such a strainer 

 could be made. Furthermore, such a strainer would be too 

 frail to stand the required pressure. 



