t>4 PREPARATION AND MOUNTING 



consequently the first step should be to experiment or* 

 various kinds. 



In gathering diatoms much labour is saved by judgment 

 and care ; hence it is desirable to get acquainted with them 

 in their growing condition, so that when recognised upon 

 the sand or other spots, they may be carefully removed by 

 the aid of the spoon or small tin scoop before described. 

 When growing upon algae or other plants, the plants and 

 diatoms together may be carried home, in which case they 

 must be simply drained and not washed or pressed, in order 

 that the diatoms be not lost. As it is always desirable to 

 examine the gathering on the ground, a " Gairdner's hand 

 microscope " with powers from 80 to 200 diameters will be 

 found very useful. The best gatherings are those which 

 represent one species abundantly. Those which are mixed 

 may be rejected, unless they are seen to contain something 

 valuable or important, as the object should be not so much 

 to supply microscopical curiosities as to collect material which 

 is available for the study of nature. 



The gathering when carried home should always be care- 

 fully examined before anything is done with it ; not only or 

 account of the additional information thus acquired, but 

 also because it often happens that a specimen should be 

 mounted in fluid (see Chapter Y.) in the condition in which 

 it is gathered, as well as cleaned and mounted in balsam 

 (Chapter IY.) and dry. 



Where the gathering is taken from sand, the whole may 

 be shaken up in water as a preliminary operation, when- 

 much of the sand will be separated by its own weight. The 

 lime test, however, should be applied ; viz. a small portion 

 of hydrochloric acid, and if there be effervescence, it must be 

 dissolved out by this means. From Alga3 and other weeds 

 diatoms may be detached by agitating the whole together 

 in a weak solution of nitric acid about one of pure acid to 

 twenty or thirty of water, as it must be sufficiently weak to 

 free the diatoms without destroying the matter to which 

 they adhere. The diatoms may then be separated by 



