1897-98-] On the Diatomacece. 363 



water poured off. This is repeated till all traces of the soap 

 have been washed away. The bottom of the beaker-glass 

 should now be covered with a white layer of greater or less 

 thickness, according to the quantity of material used. If 

 the various processes have been successfully performed, this 

 layer should consist of pure diatoms and sand. To get 

 entirely rid of the sand is next to impossible. A great 

 portion of it can be got rid of by filling the beaker-glass half- 

 full of water, and by the hand imparting to it a circular 

 motion, when the diatoms will rise in a spiral colnmn and 

 the heavier sand will gather in a small heap in the centre 

 of the bottom. The water with the diatoms can be gently 

 decanted, and this can be repeated till a fair separation has 

 taken place and you find you have a tolerably clean quantity 

 of diatoms. 



The gathering which formed the subject of this process of 

 cleaning was supposed to be one from the surface of mud on 

 the sea-shore. Of course the same treatment will suffice for 

 gatherings from other surfaces, such as stones in the water, 

 the faces of rocks, and the sides of caves. If the gathering is 

 one of higher plants to which the diatoms are attached, the 

 first process is to get the diatoms detached, which can gener- 

 ally be effected by steeping the plants in dilute nitric acid. 

 When this is done the whole of the boiling and washing 

 processes before described have to be followed. When it is 

 a gathering from a fossil deposit which has to be cleaned, and 

 the diatoms are embedded in a substance of a more or less hard 

 consistency, the first stage is the thorough pulverising of this 

 substance. This can usually be accomplished by boiling the 

 gathering, broken into small pieces, in a test tube along with 

 a pea of potash or even of common washing-soda. As the 

 diatoms are, however, liable to be destroyed in this process, 

 care must be taken to stop the boiling the moment the mass 

 is pulverised, to fill up the test tube with water, and to 

 continue the washing till all traces of the alkali have been 

 removed. The boiling with acids and washing, as before 

 described, must now be followed. In all these processes the 

 Italian proverb, Festina lente, is most applicable. 



Now that we have got them cleaned, we wish to preserve 

 them for future examination. This can be easily done in 



