362 On the Diatomacea. [Sess. 



To get rid of any organic matter which may be mixed with 

 the diatoms, the deposit in the test tube is covered with a 

 sufficient quantity of sulphuric acid, and the boiling recom- 

 menced and continued till the contents are of a dark, inky 

 colour. This colour must then be discharged, which is done 

 by dropping into the boiling sulphuric acid small grains of 

 crystals of chlorate of potash till the contents are clear. 

 This is altogether a very delicate process, and requires to be 

 gone about with great care. In boiling, the mouth of the tube 

 must be held away from the direction of the face or any part 

 of the body, as the acid is apt to be projected out of it. A 

 good plan is to have a glass stirring-rod in the tube stuck through 

 a disk of stout paper covering the mouth of the tube. The 

 chlorate of potash must also be added very carefully, and in 

 small quantities, otherwise an explosion will take place, shatter- 

 ing the tube and doing damage all around. 



The contents of the tube are now emptied into a beaker- 

 glass half-filled with water. This glass must be a thoroughly 

 tempered or annealed one, else the great heat engendered by 

 the mixing of the sulphuric acid with the water will break 

 it and cause the contents to be lost. It may be found advis- 

 able before emptying the tube into the beaker-glass to fill the 

 tube with water. This can be done without much danger by 

 allowing the water to trickle down the side of the tube. The 

 contents of the beaker-glass are now allowed to stand till all 

 the diatoms fall to the bottom. The supernatant liquid is 

 then poured off and the glass again filled with water, which, 

 after the diatoms have settled, is poured off. The process is 

 repeated till all the acid has been washed away. The sedi- 

 ment in the glass should now consist of diatoms, sand, and 

 flocculent matter. To get rid of this flocculent matter the 

 whole is again transferred to the test tube, along with a little 

 water. A small pea of hard yellow soap is added, and the 

 whole boiled for five minutes or so. In the boiling there will 

 be danger of the contents being projected out of the tube. 

 This can be obviated by using the stirring-rod, as recommended 

 in the case of the sulphuric acid. 



The contents, after having been well shaken, are poured 

 into the beaker-glass, which is filled with water, allowed to 

 stand till the diatoms have sunk to the bottom, and then the 



