( 158 ) 



NOTES AND CORRESPONDENCE. 



Ou a mode of 'vrashing and conccntratliig Diatomaceous Earths 



and Clays. — The following method which I have adopted, with 

 tolerable success, consists in making- the deposits fall through 

 a constant depth of water, in various periods of time ; thus 

 dividing the diatomes, according to their sizes, into portions 

 of several different gravities. 



Hule. — Take about a cubic inch of the clay to be examined, 

 digest it for about four hours in strong: nitric acid at a mode- 

 rate temperature ; now add gradually an equal quantity of 

 hydrochloric acid, effervescence takes place, a further action 

 on the clay ensues ; keep boiling for about three hours more, 

 occasionally stirring, and then allow the mixture to cool and 

 settle down, which it will do in about an hour ; pour off the 

 superfluous acid and wash the residue repeatedly with water, 

 so as to get rid of the remaining acid. 



The next operation is to divide the sediment into portions of 

 various specific gravities ; for this purpose it is necessary to 

 have several beakers, about 3 or 4 inches in height, and about 

 It to 2 inches in diameter; also one very large beaker, about 6 to 

 9 inches in diameter : we will call the large beaker A. Now 

 transfer the sediment into one of the small beakers, and pour 

 in water till there is just 2 inches depth of water in the glass. 

 Stir and let stand half-a-minute by the watch, and then pour 

 off carefully into the large beaker A ; repeat this about half- 

 a-dozen times, each time pouring off into A all that does not 

 fall through the 2 inches of water in the half-minute, and at 

 last the small beaker will contain only what falls through 

 2 inches of water in half-a-minute. Now let A stand about 

 half-an-hour, pour off carefully, and transfer the sediment in 

 A to another small beaker ; put 2 inches of water with it, 

 stir and let stand for 2t minutes, then pour off into A. Re- 

 peat this about six times, and there will now be another small 

 beaker containing all that falls through 2 inches of water in 

 2t minutes ; while in A is all that does not fall through that 

 distance in that period. Let A stand half-an-hour, pour off 

 and transfer the sediment to another small beaker, stir and let 

 it stand Jive minutes, pour off into A as before, and repeat 

 this as before about six times. There is now another beaker, 

 containing all that falls through 2 inches of water in 5 

 minutes. After this I do not divide them any further, but 



