OF MICROSCOPIC OBJECTS. 71 
settle perfectly and the acid poured off. All traces of the 
acid must now be washed away with pure water, when the 
remains will be Diatomacess, the sand contained in the 
guano, and a few other forms. Some of these may be 
mounted dry, as before mentioned, but the greater portion 
should be put up in Canada balsam as described in 
Chapter IV. 
Such is the ordinary method for the treatment of guano; 
but Mr. Rylands’ mode of proceeding with ordinary Diato- 
macez (before given) will be found equally successful with 
these deposits. 
The composition, however, of guano is more complex than 
the substances by which we find most of the Diatomacez 
- surrounded, and therefore a different method of treatment 
is pursued by many. The following by Mr. A. J. Roberts 
is a good one: “Guano should be first well washed with 
boiling water, either on a paper filter or by repeated affu- 
sions until the liquid come off tasteless. Boiling water is 
preferable to cold, for the heat expels air-bubbles and causes 
the deposit to settle down into a smaller space; then the 
deposit must be subjected to the action of the acids as 
directed for the preparation of earths, to get rid of the lime 
salts. The partially cleaned deposit, which is now much 
smaller in bulk, must be separated as much as possible 
from the liquid, strong sulphuric acid, in sufficient quantity 
to cover it, poured on to about the depth of half an inch, 
and heat applied and continued for some time, but the liquid 
must not be made to boil. The result will be an almost im- 
mediate blackening of the liquid, which gradually becomes 
deeper, and a dirty, inky-looking compound is ultimately 
produced. When this has taken place, chlorate of potash 
in fine powder must be dropped into the hot mixture very 
gradually until the black colour disappear. This must be 
done cautiously, for the action is so violent, that much 
spurting is occasioned; and the liquid being very corrosive, 
a tolerably capacious vessel should be used in order to keep 
‘the splashes within reasonable bounds, or serious damage to 
