SCIENCE-GOSSIP. 



163 



FLOTATION AND ROLLING OF FORAMINIFERA. 

 By G. H. Bryan, F.R.S. 



" TF a mixture of sand and Foraminifera be put 

 into water, the sand will sink and the 

 Foraminifera will float." Such is the dictum 

 which, like the now exploded nostrum about 

 softening coal in caustic potash in order to cut 

 sections, has been repeated by writers innumer- 

 able. In the hopes of preventing others from 

 wasting hours over trying to float Foraminifera 

 and sink sand when the task is hopeless, a few 

 remarks may be of use. 



The method seems very promising at the 

 commencement of the experiment, for as soon as 

 the sand falls into the water a film of floating 

 particles remains at the top. You examine them 

 under the microscope, confidently expecting to see 

 pure Foraminifera. To your disappointment you 

 find little else than pure sand ; and the more 

 carefully you follow the instructions in the books 

 about washing the salt out and drying the material 

 before " floating," the more tenaciously do these 

 sand particles cling to the surface. The writers 

 all ignore the fact that small bodies, such as 

 needles or microscopical cover - glasses, though 

 themselves heavier than water, can be easily 

 made to float on its surface, being held up by 

 "capillarity" or "surface tension"; and in the 

 case of small sand-grains there is the greatest 

 difficulty in making them sink. Unless all the 

 particles of material are made to get wetted all 

 over, it is useless to attempt to remove sand by 

 " floating." 



I have partially succeeded in avoiding this float- 

 ing sand-film by introducing the material into the 

 water through a piece of paper folded into a 

 conical funnel with its opening held below the 

 water, and finally closing the opening and remov- 

 ing the funnel with any particles of sand that 

 might be floating inside. By stirring the sand in 

 the water a number of tiny white particles 

 rose to the surface, and by skimming these 

 off, I did actually get a very small pinch of 

 nearly, but not quite, pure Foraminifera in one 

 case. Even here difficulties arise, as the sand has 

 a most unpleasant habit of carrying down bubbles 

 of air, and when these come to the surface and 

 burst, they will bring up a film of floating sand. 

 To make matters worse, bubbles of air very often 

 form in the water itself, round the sides and at the 

 bottom of the water, and these too rise and bring 

 up sand with them. By the time all these 

 difficulties have been got over it is small wonder 

 that many of the Foraminifera have filled with 

 water and sunk. 



If it is so difficult to get pure Foraminifera on to 

 the top of the water, it is much easier to effect 



a partial separation and bring them to the top 

 of the sand, by imitating as far as possible the 

 action of the waves in depositing those white 

 ridges of Foraminifera and broken shells so 

 familiar about high-water mark on our coasts. 

 This takes far less time to do, as the preliminary 

 washing and drying are avoided. By shaking the 

 material in water in a saucer or soup plate, the 

 Foraminifera and broken shells come to the top, 

 and a gentle rotation — especially if too much water 

 is avoided — will collect most of them round the 

 edges, where they can be removed with a brush. 

 If wished, it might be worth while to dry and 

 attempt to float the material thus obtained, which 

 would be more likely to succeed than treating the 

 sand in bulk. As, however, the foreign matter will 

 consist largely of broken fragments of shells and 

 debris generally, while rounded sand-grains will 

 almost entirely be left behind, it may be well to 

 try the following plan, which I have not seen 

 previously described, and which in several cases 

 where I have tried it has answered very well. 



Take a sheet of paper and, after turning over 

 one of its edges, lay it on a flat board or book. 

 In the "gutter" formed by the turned-over edge 

 place a narrow line of the dried foraminiferous 

 material and tilt the whole at a small angle to the 

 horizon, the line of material being at the top. By 

 getting this "inclined plane" at a suitable slope, 

 which can easily be done by gradually inclining 

 it till the required effect takes place, and gently 

 tapping it, the debris will slide down in small jerks 

 a little distance with each tap, but the rounded 

 Foraminifera will be set rolling and will skip com- 

 pletely off the sheet, when they can be caught in a 

 paper tray placed below for their reception. When 

 the debris have nearly reached the bottom edge 

 of the sheet they are to be tilted' back into the 

 groove at the top, and the process repeated till 

 practically the whole of the Foraminifera have 

 rolled off. This operation, depending as it does 

 on the simple principle that a rounded body will 

 roll down an inclined plane which is too rough to 

 allow a flat body to slide down it, is very easy to 

 carry out, and does not occupy one-tenth of the 

 time required for the tedious process of floating. 

 It has, moreover, the advantage that those trouble- 

 some dust filaments and wood chips are entirely 

 left behind, as also are fragments of seaweed, 

 zoophyte, etc. Even a small pinch of material 

 that has been " floated " will yield far cleaner 

 slides after being treated by the " inclined plane " 

 method. 



University College of North Wales, 

 Bangor. 



