302 THE president's address. 



Another colourless medinm with which I have lately been 

 experimenting is phosphorus. Those who are familiar with the 

 properties of this substance will readily understand that it is no 

 easy matter to obtain a successful mount of objects in such an 

 unstable medium. I am indebted to the kindness and generosity 

 of my friend Mr. Morland, certainly the most accomplished 

 manipulator of diatoms that I have ever met, for specimens 

 of finely lined diatoms mounted in pure phosphorus. The slides 

 I have were prepared about ten years ago, and although a spot 

 of partially oxidised phosphorus has appeared in one of them, 

 the diatoms are for the most part shown as clearly as though 

 the mounts had been put up only yesterday. The refractive 

 index of phosphorus is 2 -2, and it appears to have no effect 

 whatever on silicious structures. 



The valves appear to have been fixed in some way to the cover 

 glass, and consequently they do not annoy one by constantly 

 shifting their position whilst under observation, as is frequentl}" 

 the case with specimens mounted in aqueous solutions. The 

 diatoms in my cabinet mounted in phosphorus are, Aonphipleura 

 2)elh(cida, Frustidia saxonica, Pleurosigma angulation, F.formosum, 

 and Nitzschia sigmoidea. All these forms appear to full advantage 

 in this medium under my 3 mm. apochromatic of 1*43 N.A. 

 The A. 2^€^^ucidn is especially brilliant, and the other forms 

 reveal their minutest detail splendidly. If it were not for the 

 extreme difficulty of manipulation, I think it probable that 

 phosphorus w^ould rapidly become a favourite mounting medium 

 for objects of this class. 



Quinidine is, I believe, amongst the members of the Club, a 

 well-known material for the mounting of diatoms. It is perfectly 

 colourless, easilj^ manipulated, and requires no previous pre- 

 paration. Quinidine is an ideal temporary mounting medium 

 for those who prepare their own diatomaceous material. There is 

 no other substance that lends itself so readily as this to rapid 

 mounting; all that is required being to interpose a minute 

 portion of it between the cover-glass bearing the diatoms and the 

 slip, and then to fuse the quinidine by the help of a spirit lamp. 

 Immediately on cooling, the slide is ready for examination ; and 

 if it so happen that a valve has emerged from the fusing process 

 in a favourable position, it will remain fixed there, and the slide 

 will require no ringing or further protection. 



