Met eR | of Soundings for the Microscope. 145 
Dioxide (Silica), built up into the skeletons of dead organisms. 
The problem, then, presented to me was to prepare it in such a way, 
if possible, first, to show all of these objects at the same time, or 
second, to separate it into calcareous and silicious specimens, and 
this last method I found, after trial, to be the best. As my mode 
of manipulation may hereafter be of value to others possessing 
similar gatherings, I will give it in detail. 
The sounding, being in the shape of a dry powder of a light 
greyish-green colour, was placed in a suitable glass vessel and 
moderately strong Liquor Potassa poured upon it. It was now 
boiled for a few moments until I saw that the lumps present in it 
were broken up and a light mud-like sediment was the result. The 
solution of Potassa must be, of course, apportioned in strength to 
the specimen under manipulation, such as consists of many lumps 
and much organic matter will require it of greater strength than 
that which is mostly calcareous and silicious. If it be used too 
strong some of the more delicate silicious forms will be attacked, or 
even, as I have occasionally found, entirely dissolved. After it had 
boiled for a short time, as I have said, I allowed it to stand until 
the mud had settled and a tolerably clear solution was left above it. 
I now poured off most of the Liquor Potassa and replaced it by a 
strong solution of Chloride of Soda, so called. That sold by apothe- 
caries under the name of “ Labarraque’s Solution” will answer 
generally and is readily procured. This I now boiled until I found 
its action to cease. By this means the mud is so much bleached as 
to become almost white. The Potassa at first has the effect of dis- 
solying much of the organic matter present, and thus breaking up 
the lumps and setting the shells free, and the Chloride of Soda 
solution bleaches them, so that we have them clean and separated 
to such an extent that under the microscope the individual shells 
are easily recognized. I now proceeded to separate the larger from 
the smaller forms by means of the “ Elutriation” process, which 
consists in first washing off thoroughly all the Potassa and Chloride 
of Soda with pure filtered or distilled water, and shaking up the 
sediment in a glass about two inches high filled also with water. 
If now permitted to stand for a few seconds the larger forms and 
coarser sand settles, and the supernatent liquid can be poured off 
into another larger vessel. Again water is added to the first sedi- 
ment, and, in turn, removed, and this is done as many as six or 
eight times, until we see that the coarse sediment is not contami- 
nated by finer particles by the water it is shaken in remaining 
almost clear. ‘The same process is carried out with the sediment 
in the second vessel, only permitting each charge of water to stand 
longer than in the first case, as the forms are now much smaller 
and require longer to settle. In this way we may get three or 
four densities of sediment, although I found that my specimen 
