JOURNAL 
OF THE 
ROYAL MICROSCOPICAL SOCIETY. 
AUGUST 1890. 
TRANSACTIONS OF THE SOCIETY. 
VI. — On some Methods of preparing Diatoms so as to exhibit clearly 
the nature of their Markings. 
By C. Haughton Gill, F.C.S., F.R.M.S. 
( Bead 19 th March , 1890.) 
Plate YII. 
In a note communicated to the Society’s Journal for December last I 
drew attention to the fact that certain diatoms when treated as therein 
shortly described, became so “ charged ” as to clearly demonstrate that 
their markings (‘‘striae,” “dots,” &c.) were hollows or cavities of some 
kind, as they were capable of being filled with foreign matter. 
Having been asked to give more detailed particulars of methods 
and results I beg permission to submit the following. 
Diatoms may have their “ lacunae ” filled or partly filled by 
either of the methods described below, of which the third is by far the 
best as a general one. 
(1) Prussian-blue Method. — Applicable only to such diatoms as 
have very coarse markings. The cleaned and ignited diatoms are 
boiled and soaked for several hours in a strong solution of ferric 
chloride (perchloride of iron) ; then to the cooled liquid is added a 
saturated solution of potassium or sodium acetate, whereby the ferric 
EXPLANATION OF PLATE VII. 
Fig. 1. — Inner surface of a Coscinodisc “charged” with mercurous sulphide. Some 
of the cells broken away, x 825. 
„ 2. — Edge view of fragment of a Coscinodisc, showing the honeycomb structure 
of the valve, x 825. 
„ 3. — Cell-cappings of a Triceratium. The perforations (secondary markings) 
filled with mercurous sulphide, X 825. 
„ 4. — Pinnularia major (?). Stria) wholly or partially “ charged ” with mercurous 
sulphide, x 825. 
„ 5. — Stauroneis phcenicenteron with lacuna) partially charged with mercurous 
sulphide, x 1750. 
„ 6. — Cocconcma lanceolalum, partially charged with mercurous sulphide, x 825. 
„ 7. — Epithemia turgida, charged with mercurous sulphide, x 825. 
„ 8. — Pleurosigma angulatum, charged with silver sulphide, X 1750. 
„ 9. — Surirella gemma charged with silver sulphide, x 1750. 
1890. 2 H 
