HARD WI CKE 'S S CI EN CE-GO SSI P. 



217 



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ON MOUNTING DIATOMACEvE, 



By F. KITTON, Hon. F.R.M.S. 



■ N my former paper on "Clean- 

 ing Diatomacese," I omitted 

 a somewhat important hint 

 — viz., how to obtain these 

 forms in a more or less 

 clean condition without 

 acid. If the diatoms are 

 living in the gathering, it 

 should be poured into a 

 wide-necked bottle (similar 

 to those in which pomade is 

 sold), and placed close to the window. Under the 

 influence of the light, the diatoms will make their way 

 to the surface of the mud or vegetable debris, and will 

 continue to propagate (sometimes for weeks). Their 

 presence will be indicated by a film, more or less 

 thick, of a dark yellowish-green colour : this must be 

 removed' from time to time by a small dipping-tube. 

 As these papers are written for learners, I may 

 perhaps be excused if I explain how to use it. Before 

 inserting it in the bottle, the fore-finger should be 

 firmly pressed on the top, the other end being placed 

 over and almost touching the film ; withdraw the 

 finger, and the diatoms will rush into the tube; 

 replace the finger, and drop the contents into distilled 

 water or spirit. When a sufficient supply has been 

 obtained, the remainder of the gathering can, if 

 desirable, be cleaned as previously described. 



The following is a list of essentials required for 

 mounting diatoms : — 



Glass slips 3x1. 

 Thin glass discs, f and \ inch. 

 Turn-table. 

 Writing-diamond. 

 Common brass forceps. 

 Small camel-hair pencil. 

 Canada balsam. 

 Asphalt varnish. 

 Gold size. 

 Turpentine. 

 Benzine collas. 

 Gum arable. 

 Glycerine. 

 No. 154. 



.As the tyro should be content in the first instance 

 with what are termed spread slides (and for the 

 purposes of study these are the most valuable), we 

 will endeavour to explain our plan of making them. 

 The slide must be cleaned by dipping in a strong 

 solution of common soda ; wipe it dry with an old 

 linen handkerchief : this ought to be thoroughly freed 

 from soap grease by boiling in soda and water. 

 Place the slide or slides on a level surface, spread 

 evenly a small quantity of the material on the centre 

 of each slide, and leave it to dry slowly. If held over 

 the lamp it almost invariably dries in ripples, and 

 the slide is spoilt. 



But few gatherings are free from particles of sand, 

 and as their presence is the bete noire of dry mounting, 

 the following hints for their elimination may prove 

 of service. If the sand grains consist of minute 

 fragments of quartz, as is most frequently the case, 

 they may be got rid of to a great extent by first 

 placing the cleaned material in a porcelain saucer or 

 watch-glass, and, after subsidence, giving it a lateral 

 circular motion, which will produce a vortex : the 

 diatoms will rise, and may be poured off into some 

 distilled water : a repetition of the process will eli- 

 minate still more of the sand. Many valves will of 

 course be lost; but this is of little consequence when 

 they occur in abundance or the forms are large, such 

 as Eupodiscus, Coscinodiscus, Triceratium, &c. ; but 

 these can be easily picked out. If the quantity to be 

 operated upon is small, a large drop of the material may 

 be placed on a slide, and similar motion given to it, 

 and the drop tilted to one corner of the slide and 

 poured into a drop of water on another slide : 75 

 per cent, of the sand will be left behind. If the 

 sand largely predominates, two or three drops may 

 be operated upon by pouring them into the drop of 

 distilled water : repeat the process with this, and 

 a good slide will be the result. If the sand is 

 micaceous, I know of no plan that will enable us to 

 get quit of it. The rationale of this may be thus 

 explained. The diatom valve and the micaceous 

 sand consist more or less of thin plates, both of 

 which sink much less readily than the quartz sand, 



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