30 TECHNOLOGY OF THE D1AT0MACE.E. 



for it is only after a series of manipulations that it is possible to 

 ascertain its richness or sterility as regards organisms of this kind. 

 I have many times had at my disposal one or two killogrammes of 

 marine deposit, in which repeated examinations under the micro- 

 scope showed nothing, but which, after having been subjected to 

 the^ needful manipulations, have given excellent results, not as 

 regards quantity, but from the specially interesting species that 

 were extracted. 



Soundings are of many kinds and are obtained by different 

 methods. Formerly, it was and even sometimes now is, the prac- 

 tice to cover the lower side of a leaden weight (held by a slender 

 cord) with fat or hard soap, to the surface of which a small quan- 

 tity of the mud which forms the sea-bottom adheres. 



Nothing can be more detestable to thediatomist than this kind 

 of material — in the first place, because he has to get rid of the 

 grease or soap employed ; and then because it is only possible by 

 this means to place at his disposal so small a quantity, and that it 

 cannot give an idea of the richness of the bottom whence it comes. 



The fatty or resinous matters are removed by washing with 

 ether or benzine, and the soap by hot water. The sediment then 

 having been well dried, is treated with a series of acids and the 

 usual reagents. 



In general, it is by means of special sounding-leads or drags, 

 or by means of nets, that this material is obtained in any quantity 

 and appears as argillaceous or sandy mud, more or less calcareous, 

 mixed up with fine debris of all sorts belonging to the three king- 

 doms, brought up by the lead or the drag. 



All the differing materials require to be treated according to 

 their nature. 1 will therefore pass them in review, and indicate 

 the special treatment that each requires. 



Treatment of argillaceous or earthy Muds and the extraction 

 of the contained Diatoms by '' floatage."— The argillaceous or 

 earthy muds, produced of marine soundings, are rarely very rich 

 in Diatoms ; often, as I have said, they contain none at all. You 

 may assure yourself of their presence and even withdraw the 

 greater part by the method oi floatage. For this purpose the 

 material must be perfectly dried, either by exposure to sunshine or 



