476 SUMMARY OF CURRENT RESEARCHES RELATING TO 



A. 0. Cole * considers gum-styrax to be a "perfect substitute for 

 balsam," that it " yields the best possible results," and that it " may 

 be considered absolutely permanent and unalterable." The styrax 

 solution is " even easier to work with than balsam, and air-bubbles 

 are not produced in it by the application of heat." 



Smith's New Mounting Media.f— Prof. H. L. Smith has been 

 experimenting with various substances to find satisfactory media of 

 high refractive index for the mounting of diatoms, &c. The desiderata 

 at which he has aimed are : 1st, high refractive index ; 2nd, a substance 

 to be used in a fluid or semi-fluid state in the process of mounting ; 

 3rd, the property of hardening on the slide, so as to make a permanent 

 mount ; and, 4th, a proper cement, to protect it from decomposition 

 if the material is in danger from that cause by reason of exposure to 

 the air or to immersion fluids. 



Professor Smith is now assured that he has succeeded in his efforts, 

 and has produced two media, both of combinations entirely new and 

 heretofore unnoticed in chemistry. He has also devised a cement 

 for rings upon the slides to protect the media, which is also new, and 

 makes attractive mounts. 



His first medium is a transparent, colourless substance, in the 

 form of a thick fluid, which hardens by heat applied in the same way 

 as in mounting in balsam. The heat expels the fluid part of the 

 mixture, and leaves a solid which is a permanent mount, and requiring 

 no more care in subsequent handling or packing of slides than balsam. 

 The index of refraction of this medium when solidified is 2 • 00. 



The second medium is a yellow-tinted, thick fluid, similar in 

 handling to the last, and to be used and treated in the same manner, 

 but having an index of 2 • 25 ± when solidified. A perceptible brownish- 

 yellow tint remains in this medium, similar to that of pretty old 

 balsam which has been a little overheated. This medium would 

 naturally be used for special examinations of particularly difficult 

 objects, and the colour is not enough to be objectionable, though the 

 first medium, with its absolute transparency, would be preferred for 

 mure common use. Used in a fluid state, the denser medium has 

 scarcely any colour, but its refractive index is of course lowered a little. 



In either of them the resolution of Amphipleiira pellucida is made 

 with surprising ease and strength, and with light of very small 

 obliquity compared with that which has been necessary in dry or 

 balsam mounts. In short, it gives all the results which the high 

 refractive index would lead us to expect, and with none of the objec- 

 tions for cabinet use which belong to the solution of phosphorus and 

 other mixtures. 



The cement for ringing is specially devised to avoid any danger 

 of its attacking or decomposing the mounting medium. 



The following is a copy % of the report made to the State Micro- 

 scopical Society of Illinois by a committee to whom were referred 

 some slides of Diatomaceae mounted in the new media. 



* Methods of Micr. Research, Part x. (1884) p. Ivii. 

 t Amer. Mon. Micr. Journ., v. (1884) p. 71. 

 X ' The Microscope,' iv. (1884) pp. 77-8. 



