28 D1ATOMA* 



serve to clean some specimens, but it will, in general, be found 

 best to boil in nitric acid with a little bichromate of potash, 

 and subsequently in sulphuric acid and bichromate of potash, 

 with the after addition of hydrochloric acid. Occasionally a 

 certain amount of flocculent matter will be left, which it will be 

 necessary to remove with very careful heating, not boiling, in 

 a weak solution of caustic potash, and immediately pouring 

 into a large quantity of clean water and thoroughly washing. 



Marine Fossil and Sub-Plutonic Deposits, being stony and 

 possessed of very much the same physical characters, are man- 

 ipulated in the same manner. A small lump of the deposit is 

 placed in a test-tube, and covered with a strong solution of 

 caustic potash. It is then boiled for a few minutes, and usually 

 it immediately begins to break up and fall down in the shape 

 of a soft mud-like material. At once the liquid, with the sus- 

 pended fine powder, is poured off into a large quantity of clean 

 hot water, and if the whole of the lump has not broken down 

 into a powder, what remains has a little water poured over it in 

 the test-tube, and it is again boiled. It will be found that a 

 little more will now crumble off. This is added to the rest in 

 the large vessel, and if the lump has not now broken down, it 

 is again boiled in the alkaline solution and in water alternately, 

 until it has all been disintegrated. It is then all permitted to 

 settle for at least three hours, when it is thoroughly washed and 

 boiled in hydrochloric acid for about half an hour. There is 

 then added an equal amount of nitric acid, and the boiling con- 

 tinued for a short time. It is then washed and heated in sul- 

 phuric acid, with the addition of bichromate of potash and 

 hydrochloric acid. 



All mixed gatherings of diatomaceoe, and particularly all 

 muds and deposits, should be separated into densities, so that 

 for the most part the larger forms are collected together, free 

 from sand, and separate from the smaller species and broken 

 specimens. This is done by using a number of beaker glasses, 

 of various sizes, in the following manner: Into a one-ounce 

 beaker the cleaned diatoms are placed, and the vessel filled with 

 water. It is then well stirred up by means of a glass rod, and, 

 after resting about five seconds, poured off carefully into a 

 six-ounce vessel, so as not to disturb the sand which has settled. 



