~ Monthly Mi iT 
182 Transactions of the pele Re he 
would probably be found in their silicious structure, and this ex- 
pectation, rather than any anxiety to see dots that others had not 
discerned, interested me in the Pinnularian inquiry. 
One portion of such an investigation obviously relates to the. 
patterns which can be obtained by purely chemical processes, and 
without the intervention of any kind of life. 
In this paper those forms only which occur in Schultze’s artificial 
diatoms will be alluded to, and it may be as well to premise that 
although no diatom is likely to obtain its silica exactly in that 
way—that is by means of a silicic fluoride—Schultze’s formations 
may still throw out much light upon the whole subject. 
To obtain the artificial diatoms, powdered glass and fluor spar 
are acted upon by sulphuric acid, or hydric sulphate as the new 
school of chemistry prefer to call it. If no heat is used, the silicic 
fluoride gas rises slowly, and if allowed to impinge against threads 
of cotton moistened with water, a decomposition takes place, “ one 
third of the silicon unites with the oxygen of the water, and is 
thrown down.”* If the gas is passed through water the precipi- 
tation takes place in white flakes quickly choking up a small tube. 
When the moist cotton threads are used, and the process goes on 
slowly, a great quantity of irregular sausage-like tubes are formed, 
and when these are well washed, to get rid of the hydric fluo-silicate, 
and crushed under a covering slide to obtain surfaces flat enough 
for convenient examination, the diatom patterns will be seen with 
various powers from a 3rds to the highest that are made. 
The Society will excuse in these last remarks my repeating some 
matters that are now old, and which has been done to make the 
subject more intelligible to that, I fear, very numerous class of 
microscopists who have not paid to Schultze’s artificial diatoms the 
attention they deserve. 
The mode of their production just described will suffice to indi- 
cate that the circumstances determining the patterns in which the 
silica is precipitated will depend upon conditions presenting only 
slight differences. If the whole process is carried on in a room 
of ordinary temperature, say about 60° or 70°, and completed in a 
few hours, changes resulting from more or less heat will have 
little effect. The rate at which the silicic gas is evolved, the quan- 
tity of moisture it meets on the cotton threads, and such facts as 
the closer or looser arrangement of those threads, would seem to be 
the chief causes of any modification that occurs. Thus we may 
safely ascribe all the patterns we obtain to very slight chemical and 
physical conditions of decomposition and deposition, and yet what 
varieties of arrangement and size of dots or beads we obtam. The 
following is a description of some of the varieties in a single slide. 
The sizes are apparent with a magnification of about 700. 
* Barff’s ‘ Chemistry.’ 
