J. M. Blake — Picking Out and Mounting Diatoms. 53Y 



with the fingers must be avoided. The covers are now stood 

 on edge to drain and dry. Then a small central ring may be 

 spun on them, and also a marginal ring to be mentioned later. 



In this way any desired number of diatoms can be collected 

 and located. It is well to have an intermediate stamping 

 ground for temporarily depositing the selected diatoms where 

 they can be cleared from adhering fragments before finally 

 locating them. It is important to have all these cover glasses 

 of the same thickness so that no time will be lost in focusing 

 as we pass from one to the other. 



One difficulty in picking up from a diatom spread will be 

 found due to adhesion to the glass surface. This adhesion 

 is caused by dissolved silica, or by some other soluble substance 

 which may come from the glass surfaces, or from the water in 

 which the diatoms are suspended. We may prevent this 

 adhesion in part, by repeated settlings from freshly distilled 

 water; but at the best, some of the more delicate shells will 

 often break before they can be detached. 



The writer has recently tried a plan which promises to be a 

 help in such cases. This plan is to grind clown thin slips of 

 baked pipe clay or similar material. This material is then 

 finely surfaced and ignited to drive off moisture. These slips 

 may be blackened by charring sugar solution which can be 

 soaked into them. They are then scrubbed in order to 

 remove adhering particles, and again heated to drive off 

 moisture. The diatom-spreading pipette is then drawn across 

 the surface and the liquid is at once absorbed before it has 

 time to dry on the surface and cause adhesion of the diatoms. 

 Porous arc-light carbon may be ground down thin and used 

 for this purpose. Reflected light must be used over these 

 opaque surfaces. A two-thirds objective will give sufficient 

 working space, and the eye-piece should be an erecting one. 



Monobromide of naphthaline has usually been regarded as a 

 difficult mountant to make secure. Several of the monobromide 

 mounts made by the writer, however, in 1895 have kept in 

 good order up to this date. For this reason it may be of 

 interest to give some account of the method used in preparing 

 them. They were sealed with gelatine. The refraction power 

 of the unmixed monobromide used appears not to have 

 suffered by lapse of time. Loss of refractive power has 

 been reported to have occurred when a wax seal was employed. 



The glass covers that have been coated with thin gelatine 

 in the way that has been described are next given a marginal 

 ring, and the reception slide itself is also given a preparatory 

 ring. This treatment secures reliable contact of gelatine 

 and glass, as both gelatine rings are dried before the 

 monobromide is applied, A binding ring of warm gelatine 



