TJic Diatoms of Nebraska 25 



out. By this method they may be prepared much more quickly 

 than by treating with acid. When there is sufficient heat, as with 

 a gas flame, the coverglass may be laid on a flat piece of iron (the 

 writer has used the blade of an old table knife) and held in the 

 flame. When first heated the material turns black. It should be 

 heated until the blackness disappears. If the heat of the flame is 

 not sufficient, as is likely to be the case with an alcohol lamp, it 

 may be increased by the use of a blowpipe. If the coverglass is 

 held on a piece of silver, it will heat much more readily, owing to 

 the greater conductivity of the silver. For this purpose the writer 

 has used an old silver quarter dollar with a hole in it, a wire being 

 fixed in the hole for a handle. In using a blowpipe the flame 

 should be directed on the under side of the metal on which the 

 coverglass is lying and not directly on the coverglass. 



Nearly all of the fossil diatoms found in Nebraska are mixed 

 with limestone or some form of calcium carbonate. This must be 

 removed, for there is often so much of it that the diatoms are 

 hidden entirely. This may be done by treating with hydrochloric 

 acid. The method is the same as that for using nitric acid except 

 that it is not necessary to heat it. 



When dried on the coverglass they may be mounted in Canada 

 balsam, but the markings are seen much more easily if mounted 

 in styrax.^ 



1 Styrax can be procured only in the crude state and must be pre- 

 pared for use. The first step in preparing it is to spread a thin coating 

 of it on a pane of glass or a plate and allow it to dry until all of the 

 v/ater has been removed. It is then dissolved in a mixture of equal parts 

 of benzine and alcohol, or sulphuric ether and absolute alcohol. The 

 solution is then filtered through filter paper. If it is so thick that it will 

 not pass through the fi'ter paper readily, more of the alcohol and ether may 

 be added. After filtering it is ready for use. A quantity may be made up 

 at one time since it will keep indefinitely. A drop of the styrax is placed 

 on the coverglass containing the diatoms. If it becomes opaque at first 

 it must be allowed to stand until it becomes clear. This may require sev- 

 eral hours. This clearing may be hastened by heating gent'y- When 

 cleared it is placed on a slide. The slide should then be heated until 

 the volatile portion of the styrax solution is driven ofif. This will cause 

 bubbles under the coverglass and the heating should be continued until 

 the bubbles cease to form. When cooled the bubbles will disappear. 



