1897-98-] On the Diatomace<z. 361 



I shall suppose the gathering to be a fresh one, taken from 

 the surface of mud on the sea-shore. There will be mud and 

 sand and small stones mixed up with the diatoms. The 

 gathering should not have been allowed to get dry. A test 

 tube of large size is taken, and a quantity of the gathering put 

 into it : it is then filled to within an inch or so of the top 

 with soft filtered water ; if the water is what is called ha,7'd, it 

 should be boiled before being filtered. The tube is vigorously 

 shaken, and then allowed to rest for half a minute till the 

 heavy particles fall to the bottom. The supernatant liquid is 

 then poured into another glass vessel, carrying with it a 

 quantity of the diatoms. The tube is again filled with water 

 and again shaken, and the supernatant fluid as before poured 

 into the other glass vessel. This process is repeated till it 

 is supposed all the diatoms have been separated from the 

 heavier matter and carried off into the other vessel. What 

 remains in the test tube is thrown away, and the tube thor- 

 oughly washed out. The vessel into which the supernatant 

 fluid from the test tube has from time to time been poured is 

 allowed to remain at rest for an hour or so, till all the diatoms 

 have sunk to the bottom. The water is then carefully poured 

 off, except so much as may be necessary to wash the sediment 

 back into the test tube. The tube may then be allowed to 

 remain at rest till the diatoms settle down, when the re- 

 mainder of the water can be poured off. The sediment in the 

 test tube is then covered with nitric acid to a depth of from 

 half an inch to an inch, according to the quantity to be 

 operated upon. The tube is then exposed to the flame of 

 a spirit lamp and the contents boiled from five to ten minutes. 

 The fumes given off during this process are very deleterious, 

 and must not on any account be inhaled nor allowed to spread 

 in the room. In boiling, care must be taken that no solid 

 matter in the tube is presented to the flame, otherwise the 

 tube will crack. With care a tube of English make will last 

 a long time. When the tube is cool after the boiling, it is 

 filled with water and allowed to stand for an hour or so till 

 the diatoms settle : the water is then poured off, and this 

 process is repeated till the whole of the acid is washed away. 

 As this water will be highly acidulated, care must be taken as 

 to how it is disposed of. 



