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 Diatomacese, 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 gnano; 

 but Mr. Rylands' mode of proceeding with ordinary Diato- 

 maceaB (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 Diatomaceaa 

 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 mnch 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 



