1884.] 



MICROSCOPICAL JOURNAL. 



71 



NiagarcB^ was compared with some 

 of the same diatoms from Cleveland 

 mounted in storax. The markings 

 were much more distinct in the last- 

 mentioned slide. A slide was also 

 prepared with diatoms from the 

 Sandwich Islands, and as some of the 

 species are very beautiful we have 

 become quite familiar with their ap- 

 pearance in balsam, and there can be 

 no question of the superiority of 

 storax as shown by this mount. The 

 same may be said of other mounts, 

 not all of diatoms, for other objects 

 were mounted at the same time. 

 Polycystina for example, showed ex- 

 ceedingly well in the storax. We 

 therefore commend the use of storax 

 or styrax, as it is indiftei^ently called, 

 for mounting when a medium of 

 higher refractive index than balsam 

 is required. 



New Mounting' Media. 



Professor H. L. Smith has been 

 expending much time and labor in 

 experimenting with various substan- 

 ces, searching for satisfactory media 

 of high refractive index for the mount- 

 ing of diatoms and similar objects. 

 The desiderata at which he has aimed 

 are: ist, high refractive index; 2d, 

 a substance to be used in a fluid or 

 semi-fluid state in the process of 

 mounting ; 3d, the property of hard- 

 ening on the slide so as to make a 

 permanent mount ; and 4th, a proper 

 cement to pr^otect it from decomposi- 

 tion if the material is in danger from 

 that cause by reason of exposure to 

 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 here- 

 tofore unnoticed in chemistry. He 

 has also devised a cement for rings 

 upon the slides to protect the media, 

 which is also new, and makes attract- 

 ive inounts. 



His first medium is a transparent, 

 colorless substance in the form of a 

 thick fluid, which hardens by heat 



applied in the same way as in mount- 

 ing 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 subse- 

 quent handling or packing of slides 

 than balsam. The index of refrac- 

 tion of this medium, when solidified, 

 is 3.00. 



The second medium is a yellow 

 tinted, thick fluid, similar in hand- 

 ling to the last, and to be used and 

 treated in the same manner, but hav- 

 ing an index of 3.25 + when solidi- 

 fied. A perceptible brownish-yellow 

 tint remains in this medium, similar 

 to that of pretty old balsam ^vhich has 

 been a little overheated. This me- 

 dium would naturally be used for spec- 

 ial examinations of particularly difli- 

 cult objects, and the color is not 

 enough to be objectionable, though 

 the first medium, with its absolute 

 transparence, would be preferred for 

 more common use. Used in a fluid 

 state, the denser medium has scarcely 

 any color, but its refractive index is, 

 of course, lowered a little. 



In either of them the resolution of 

 Amphipleura pelhtcida 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 

 i-efractive index would lead us to ex- 

 pect, and with none of the objections 

 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 at- 

 tacking or decomposing the mounting 

 medium, and makes the whole a com- 

 plete success. We have reason to be- 

 lieve that Professor Smith will soon 

 make arrangements for putting these 

 materials within the reach of all mi- 

 croscopists. J. D. C. 



Crystals of Arsenic. 



The white arsenic of commerce is 

 made up of crystals, but it is seldom 



