232 How to prepare Specimens of Diafomacese for 



flocculent matter present besides the diatoms and sand, this can be 

 removed by boiling for a few seconds in a weak solution of caustic 

 potash, and washing quickly' and thoroughly with plenty of clean 

 water. When we have recent gatherings of filamentous or stipitate 

 forms of Diatomaceae, which we desire to preserve in the natural 

 condition, they should be immersed for about twenty-four hours in 

 alcohol to dissolve out the endochrome. If this does not answer, it 

 will be well to soak the mass of diatoms or plants upon which they 

 are adherent in a solution of hypochlorite of soda, an impure variety 

 of which is sold in the shops under the name of Labarraque's disin- 

 fectant, for about the same length of time. This will generally 

 destroy all coloui', and leave the specimens transparent. It is best, 

 however, in many cases not to remove the endochrome, but leave it, 

 and mount the specimens in such a way as to show them in as 

 natural a condition as possible. How this may be done will be 

 described hereafter. 



Guanos. — The preparation of these substances, so as to obtain 

 the microscopic organisms they may contain, is rather difficult, 

 tedious, and dirty, and should only be undertaken by a person 

 somewhat versed in chemical manipulations, and in a proper room 

 as a laboratory, where there is no danger of harm resulting from 

 the fumes evolved. As the ammoniacal guanos are those which 

 contain the most diatoms, and consequently which answer best to 

 clean, we will begin with them, and take as a type that which comes 

 from the islands on the coast of Peru. As it comes into commerce 

 this guano is a moist powder of a light iron -rust colour, smelling 

 strongly of ammonia, and having scattered throughout its mass 

 lumps of ammoniacal salts of a more or less solid consistency. The 

 guano should be thinly spread out upon a stiff piece of paper and 

 exposed to the air, and, preferably, to a moderate heat for several 

 days or even weeks. In this way most of the moisture and much 

 of the ammonia wall evaporate, and less acid will be required to 

 clean the guano. It will now have become mucli lighter in colour, 

 and crumble to a dry powder. A tin pan is now about half filled 

 with a solution of common washing soda in clean filtered water, 

 and placed over some source of heat, as on a stove. The strength 

 of this solution is not a matter of any great moment, and must vary 

 with the guano manipulated. As soon as it begins to boil, the 

 guano is dropped gradually in, a httle at a time, while the Hquid is 

 stu-red with a glass rod or stick of wood. Considerable efiervescence 

 takes place, ammonia being given off, and therefore it must be kept 

 continually stirred, and care exercised to prevent its boiling over. 

 After a while it is poured into a plentiful supply of clean water and 

 •washed therewith several times, care being taken to permit all of 

 the diatoms to settle. As soon as the wash-water is only slightly 

 coloured, the guano is transferred to a good-sized evaporating dish, 



