304: THE MICROSCOPE AND ITS REVELATIONS. 



colored. The deposit is then to be treated, in a flask or test-tube, with 

 Hydrochloric (muriatic) acid; and after the first effervescence is over, a. 

 gentle heat may be applied. As soon as the action has ceased, and time 

 has been given for the sediment to subside, the acid should be poured off, 

 and another portion added; and this should be repeated as often as any 

 effect is produced. When hydrochloric acid ceases to act, strong Nitric 

 acid ^ should be substituted; and after the first effervescence is over, a 

 continued heat of about 200 should be applied for some hours. When 

 sufficient time has been given for subsidence, the acid may be poured off 

 and the sediment treated with another portion: and this is to be repeated 

 until no further action takes place. The sediment is then to be washed 

 until all trace of the acid is removed: and, if there have been no admix- 

 ture of siliceous sand in the earth or guano, this sediment will consist 

 almost entirely of Diatomacece, with the addition, perhaps, of Sponge- 

 spicules. The separation of siliceous sand, and the subdivision of the 



ElD. 132 



Fossil Diatomaceae, etc., from Mourne Mountain, Ireland: a, a, a, Gaillonella (Melosira) pro- 

 cera, and G. granulata; d, d, d, G. biseriata (side view); b, b, Surirella plicata; c, S. craticula; fc, 

 S. caledonica; e, Gomphonema gracile;/, Cocconetna f usidium ; g, Tabellaria vulgaris; h, Pinnu- 

 laria dactylus ; i, P. nobilis ; I, Synedra ulna. 



entire aggregate of Dia'.oms into the larger and the finer kinds, may be 

 accomplished by stirring the sediment in a tall jar of water, and then, 

 while it is still in motion, pouring off the supernatant fluid as soon as the 

 coarser particles have subsided; this fluid should be set aside, and, as 

 soon as a finer sediment has subsided, it should again be poured off; and 

 this process may be repeated three or four times at increasing intervals, 

 until no further sediment subsides after the lapse of half an hour. The 

 first sediment will probably contain all the sandy particles, with, perhaps, 

 some of the largest Diatoms, which may be picked out from among them; 

 and the subsequent sediments will consist almost exclusively of Diatoms, 

 the sizes of which will be so graduated, that the earliest sediments may 

 be examined with the lower powers, the next with medium powers, while 



