288 PRACTICAL MICROSCOPY. 



hazel nuts ; but the apparatus is not then quite so effective 

 or rapid. 



The mercury may indeed be dispensed with altogether 

 by the use of a plate of ground-glass in lieu of the grooved 

 base-board, but in this case the bell-jar must have a strong 

 and well-ground welt round its open mouth, perfect adhesion 

 between the two being secured by means of a coating of 

 grease. 



There is a very good form of desiccator which may be 

 obtained from almost every dealer in chemical apparatus. 

 The lower portion contains the desiccating material, over 

 which is placed a sheet of perforated zinc, while the cover 

 is ground truly, and fits as a cap or lid upon the lower half. 

 Perhaps this form would suit the majority of our readers, 

 more especially if combined with the use of chloride of 

 calcium as the desiccating agent. 



The preparation to be dried is placed upon the shelf 

 (Fig. 238) above the desiccating material, covered with the 

 bell-jar, and left to itself for twelve or twenty-four hours. 



In dry-mounting it is absolutely necessary to eliminate 

 all the moisture, for many objects mounted in a damp state 

 often become covered in a few months with a dense growth 

 of fungi, or the cover-glass becomes obscured to such an 

 extent that the object is seen as through a fog. This often 

 happens also when a cardboard cell or wooden slide is 

 used. 



Let us now proceed to illustrate the foregoing by the 

 process for mounting diatoms given in the 'American 

 Journal of Microscopy,' April 1880. 



The process of cleaning diatoms requires time, skill, 

 patience, and personal experience, in addition to what may 

 be learned from others. After trying for a long time to 

 dispose of sand and mud the novice will be more careful in 

 collecting. After an explosion or two, involving the loss of 



