Answers to Queries. 7r 
slide when the frustules have been got into the desired positions ; 
but the slide must previously be prepared with a wash of very 
weak gum tragacanth, or gum acacia, or water, or isinglass and 
water, and allowed to become almost dry before arranging the 
diatoms, either singly or in patterns, on the centre of the slide. 
And then the breath is just sufficient to moisten the very thin 
layer of adhesive matter and fix the diatoms, so that when the 
benzole, etc., is applied they will not float away. Another plan is 
to use some few drops of the gum-water in the last washing of the 
diatoms. I recommend your readers to refer to Vol. III. of the 
Journal of Microscopy, pp. 138, 229, and Davies ‘On Mounting 
Microscopic Objects.” EX. |W.) Lert, M.A, 
321.—Cleaning Diatoms.— For large forms, boil in pure soap ; 
let the diatoms settle, and then pour off the soap and water. But 
for small forms I use aqua ammoniez. te 
322.—Bleaching Diatoms.—Try by burning (deflagrate) with 
potassium nitrate (saltpetre) in small quantities at a time. Sul- 
phate of potassium and pure diatoms will be left. The sulphate 
an easily be washed away by the use of plenty of water. V. A. L. 
323.—Barbadoes Earth.—I find a saturated solution of citric 
acid acts on the iron more promptly than the mineral acids. 
Via At Te 
323.—Cleaning and Mounting Polycistina.—The “earth” 
should be broken into small pieces, about the size of a nut; boil 
for half-an-hour to one hour, in a strong solution of common 
“washing soda”; pour off the disintegrated portions into a large 
vessel, containing clean water from time to time, and repeat the 
boiling in soda, as also the pouring off, until the whole mass is 
perfectly broken up. When all the material in the large flask or 
vessel shall have thoroughly settled down, it should be subjected 
to several washings in order to remove the soda, the material 
being allowed to settle thoroughly after each washing. It should 
then be removed to a beaker or wide-mouthed bottle, which 
should be filled up with water, and after being thoroughly stirred 
or shaken up, the material should be allowed to settle for thirty 
‘seconds only, and the supernatant fluid and its floating particles 
poured off into a large vessel. Repeat this three or four times, 
and it will give the heaviest density of sand and _ polycistina. 
Repeat this process with the matter in a large vessel, allowing it to 
settle for two and a-half to three minutes, and the density con- 
taining the small polycistina will be obtained. Treat the remain- 
ing matter the same, and allow it to settle in six inches of water 
for twenty minutes, and the density, consisting of the dédris of 
Polycistina and of diatoms, will result. Now, boil each separate 
Sediment in nitric acid for fifteen or twenty minutes, remove all 
