BY CHRISTOPHER JOHNSTON*. 37 



figuration and such rare beauty in design and ornamentation. 

 One o! these Diatoms, the HeliopeUa, bo much admired, lias 

 been selected by a distinguished author to grace the front ; 

 of bisadmirable work on the microscope. 



It must be apparent that no one procrnstean method of 

 securing the prize can be made applicable in the busin< 

 "preparation." The extreme delicacy of Amphipleura forbids 

 the rough boiling which Goscinodiscus invites; the free i 

 forms of any kind in "pure gatherings" obviously require 

 nothing more than the destruction of the organic part, else the 

 fairy-like embossing, as shown in lines or dots, is blurred, or 

 disappears; wdiile the so-called Diatomaccous "earths " or clays 

 often tenaceously resist the deliverance of the imbedded g< 

 made adherent by a filmy, glassy cement, the product of time, 

 an alkali, and a portion of the seeming lithophytes of other 

 epochs. A lacustrine deposit may be washed out clean with 

 water, but rock must be softened and sulphate of liine removed 

 by boiling chlorhydric acid. 



In general, the business of preparation involves two distinct 

 processes: first, the liberation of the Diatoms (as we shall 

 henceforth, for convenience, call the siliceous skeletons of the 

 Diatomacece) from all extraneous matters, with the exception of 

 amorphous silex or some silicates; and, secondly, the complete 

 isolation of the Diatoms themselves. The former is, at times, 

 toilsome and disagreeable, by reason of acid fumes which arise 

 in its course; the latter is t< dious, and like the other, time-con- 

 suming. But both call for a clear knowledge of method and 

 precise executive manipulation, and both demand of the oper- 

 ator an intelligent adaptation of means to an end, and the 

 patience with which the attainment of the end is made possible. 



The simplest methods of cleaning are not always the most 



—for example, the rescuing of Diatoms from among the 

 fstince of Barbadoes,— nor the most complicated always 



the most difficult, as. tor instance, the treatment required by a 



sulphate of lime guano known here as the "Algoa Bay.' 1 Lei 



us, however, attempt to make the several methods distinctly 

 comprehensible, although in so doing we run the risk of 



emulating the tediousness of " neighbor V. 



Apparatus >nni Chemical V ■•'</'. Guided by our experi- 



