1S85.] 



MICEOSCOPICAL JOURNAL. 



Diatomaccie,' published \ni\\e Journ. 

 Postal Micr. Soc.^ the following in- 

 structions are given for preparing the 

 highly refractive solution of phospho- 

 rus for mounting diatoms, etc. The 

 author gives the refractive indices of 

 various media employed as balsam 

 1 .54, iodide of mercury solution i .68, 

 phosphorus 2.1. He then says: — 



' It is necessary to procure clean, 

 semi-transparent phosphorus, and 

 having cut ofl', under water, some 

 large pieces with a pen-knife, place 

 them for a few seconds on a piece of 

 white blotting paper, to free them 

 from the slightest suspicion of water. 

 Before commencing the operator 

 should be provided jvith a small ba- 

 sin of water in which to place any 

 article that has been touched with the 

 phosphorus solution to prevent acci- 

 dental combustion, and, as this me- 

 dium is liable to oxidation, it is better 

 to make but a small portion at a time ; 

 that is to say, one drachm of phos- 

 phorus to two drachms of bisulphide 

 of carbon. When the former is quite 

 dissolved, slightly damp a piece of 

 filtering paper with bisulphide of car- 

 bon, and with a very small glass fun- 

 nel placed in the neck of a stoppered 

 bottle carefully filter the solution. 

 Place the glass funnel and the filter- 

 ing paper, when used, in the basin of 

 water to prevent accident. Suppos- 

 ing the diatoms are preserved in a 

 small tube of water and spirit, all that 

 is required is to place a drop of the 

 fluid on the cover-glass, and slowly 

 evaporate the medium over the flame 

 of a spirit-lamp or jet of gas. When 

 the cover-glass has become quite cool, 

 place on the mai'gin of its edge a 

 mere speck of Canada balsam, the ob- 

 ject of which is to keep the cover, 

 with its surface covered with diatoms, 

 face downwards, in the centre of the 

 glass slip. By means of a pipette, 

 take a few drops of the solution of 

 phosphorus and place them at the 

 edge of the cover, and by capillary 

 attraction they will be immediately 

 drawn under, displacing the air in 

 their progress. 



' Having ascertained that the di- 

 atoms aie completely immersed in 

 the medium, remove all superfluous 

 particles of phosphorus with a piece 

 of blotting-paper, damped with bi- 

 sulphide of carbon, and consign it 

 also to a basin of water. Finally, 

 place the slide on the turn-table, and 

 with a brush dipped in Walton's glu- 

 cine or Ray's coaguline, (the former 

 we think the best,) draw a ring round 

 the edge of the cover-glass. In all 

 probability, this will be dry in the 

 course of six hours, when, if neces- 

 sary, another ring of the cement may 

 be added, covering this with a further 

 application of shellac varnish, or as- 

 phalt, as a last layer, any colored 

 cement that the fancy of the operator 

 may dictate. 



' Diatoms that are almost indistin- 

 guishable in balsam show quite clearly 

 in this medium. The structure of 

 Heliopelta and Omphalopelta are 

 brought out in a remarkable manner, 

 and the same may be said of many of 

 the varieties of Navicular Pleurosig- 

 ma^ and Nitzschia.'' 



[We are not acquainted with either 

 of the cements mentioned above, and 

 the reader might find it difficult to 

 obtain them. Although we have not 

 had any experience in mounting with 

 the solution of phosphorus, "we ven- 

 ture to suggest a cement which will 

 unquestionably serve perfectly well 

 for the purpose. It is a solution of 

 ordinary gelatin in water, colored 

 slightly with potassic dichromate. A 

 rather thick solution can be used to 

 make a cell, if used warm on a warmed 

 slide. When the mount is finished 

 exposure to light for a short time 

 after the gelatin is dry renders it quite 

 insoluble. We can guarantee a cell 

 thus made to serve the purpose well, 

 for we once had occasion to make 

 some large bisulphide of carbon prisms 

 for a spectroscope. The prisms were 

 cast in brass, and two sides were of 

 plate glass, cemented on with com- 

 mon glue, to which some potassic di- 

 chromate had been added. The ce- 



