52 DIATOMACE.L. 



been prepared with acids, for the diatoms thus treated when 

 mounted appear much sharper and cleaner. The amount of 

 heat, if the diatoms are rigidly siliceous, as most of them are, 

 mav be the full power of an ordinary alcohol flame continued 

 for some time, but if they are imperfectly siliceous, care must 

 be exercised in the burning. 



I invariably use old balsam for mounting, just as bought 

 from the shops, especially if I wish to have a specimen which 

 will bear immediate handling, or be ready to be sent off soon 

 as mounted. Allowing then the cover to cool, while the slide is 

 being cleaned to receive it, I place a drop of the balsam, which 

 must not be fluid, only viscous, on the middle of the slide, and 

 now with this pick up the cover from the little stand where it 

 has been heated. The diatoms will be so fastened by the heat- 

 ing, that but few will flow out from under the cover, if any, in 

 the subsequent treatment. I now hold the slide over the flame 

 of the lamp (which should be much smaller than when used for 

 the burning) until not only all under the cover is a mass of 

 small bubbles, but until very large bubbles, balsam steam, ap- 

 pear; the flame is removed soon as the bubbles are observed all 

 running to one edge. I press down the cover at this place by 

 a mounted pin, and start them in the opposite direction. This 

 may seem unnecessary, but long experience shows that this is 

 the better way to get rid of them; during this the slide is held 

 somewhat obliquely, the cover is kept from slipping by the 

 pin, and if all the bubbles do not disappear, then with a very 

 small flame heat is applied just beneath the obstinate ones, the 

 slide being held slanting, and that part upwards where the 

 bubbles are nearest the edge of the cover. The description is 

 longer than the actual process, and the slide when cool is ready 

 for immediate use. Perhaps I am wedded to old ways, but 

 after trial of fluid balsams, without heat, I have always come 

 back to the old way; still, for selected diatoms, some of these 

 preparations of balsam are good. If the diatoms are to be 

 mounted dry, always the best way, if for real study, I make a 

 ring of the zinc white in balsam, (sold by the opticians,) and 

 which in a moment or two is sufficiently hard to receive the 

 cover, (ti'il never runs in; after standing an hour or two I give a 

 finishing ring of same, or the usual black varnish on the outside. 



