PROCEEDINGS OF SOCIETIES. 239 
a few ounces of water, hot, and rendered thoroughly alkaline with 
common washing soda; this plan frequently answers, causing the 
lumps to swell, gradually separating into layers, and finally fall- 
ing asunder into a pulpy mass. The strong soda ley must now 
be removed by frequent washing, and afterwards boiled in a 
florence flask with pure nitric acid; the whole must afterwards be 
transferred to a large stoppered vessel and violently shaken, in 
order to break up the minute fragments of dirt, and thus to free 
the siliceous diatoms. After shaking, allow the vessel to stand 
for a space of time, varying from half to one hour or more, accord- 
ing to the size and density of the valves; the diatoms having sub- 
sided, the dirty water is drawn off with a syphon, fresh water 
added, and the shaking repeated. The whole secret indeed depends 
upon getting rid of the impurities by this violent shaking and 
washing ; when quite free from all impurities the material may be 
transferred to a test-tube, washed in distilled water, and fimally 
mounted. 
Sometimes the binding material may be siliceous, in which 
ease the only plan is to adopt Professor Bailey’s caustic soda 
method, viz., boiling the material very slightly in a strong solu- 
tion of caustic soda or potash, and suddenly pouring it into a 
large quantity of cold water to check the action of the alkali on 
the siliceous diatoms; the after process of boiling in nitric acid 
and shaking up is nearly similar to that already described. _ 
Some of the Barbadoes and Oregon deposits were mentioned as 
being alike unacted upon by either acids or alkalies, in which case 
Mr. Norman had found a plan of long-continued boiling in plain 
water as the only adoptable method to break the lumps down. 
The gentle abrasion of the small particles during the boiling freed 
many of the valves which would have been destroyed had more 
force have been used. The finely abraded powder is to be boiled 
in acid as before mentioned; a previous boiling in soda or liquid 
ammonia had in some cases been found beneficial. 
Should oxide of iron be present, which is shown by its red or 
yellow colour, muriatic acid must be used; the employment of 
sulphuric acid is always to be avoided should the presence of any 
lime be suspected. Gypsum or sulphate of lime in small quan- 
tities may be removed, by boiling in a solution of soda and then 
with nitric acid. 
Should vegetable matter exist, it must be charred by boiling in 
strong sulphuric acid, and afterwards adding with caution finely 
powdered chlorate of potash. 
When after careful boiling in acids there remains much floccu- 
lent matter, which falls with the diatoms and is difficult to get 
rid of, a few drops of liquid ammonia shaken up with the material 
causes the filth to remain a long time suspended, and may thus 
be drawn off with the water. 
Mr. Hanwell’s paper on the “ Gastric Teeth of Insects” was 
illustrated by numerous slides of his own preparing, including 
those of the wasp, bee, cricket, cockroach, Dysticus, Staphylinus, 
