898 SUMMARY OF CURBENT RESEARCHES RELATING TO 



colour. Pyrogallic acid, alcohol, and hydrochloric acid give, with 

 heat, a blue-green stain. Carbolic acid, alcohol, and hydrochloric 

 acid a yellowish green. 



Modification of Semper's Method of making Dry Preparations.* 

 — Prof. O. P. Hay, finding that preparations made according to Sem- 

 per's method often present a dingy, weatherbeaten aspect, recommends 

 that the method should be completed by saturating the preparation 

 with a solid that fills up the pores and binds the parts together. The 

 solid which he employs is a mixture of Canada balsam, paraffin, and 

 vaseline, but it is probable that a soft paraffin will in most cases do 

 quite well. It is necessary that the mixture shall melt at about 

 46° C. 



Freeing Objects from Air.t— D. S. W. recommends the follow- 

 ing plan for mounting objects containing a considerable quantity of 

 air : — 



" Take, for example, a collection of IstJimia, or some other diatom. 

 The valves enclose so much air as to cause them to float upon water, 

 and it must be extracted, for until they sink it is impossible to wash 

 them. Drive from water all the air you can by a good boiling for 

 about five minutes, allow the water to cool so as to be in condition to 

 absorb air, and without delay drop in the diatoms. The water will 

 extract the air from them and they will go to the bottom. Then add 

 to the water a little dissolved chloride of soda, and with an occasional 

 shake up, you will find the material pretty well cleaned and bleached 

 in one hour. Wash thoroughly in several changes of water. 



Take a drachm of redistilled alcohol and add thereto two drops 

 of dissolved gum arable. With a sharpened stick place a small 

 quantity on the centre of a cleaned slide. It will spread out and 

 the alcohol will quickly evaporate, leaving a very thin film of the 

 gum. On this gummed spot place a drop of your cleaned diatoms, 

 and see that they are thoroughly dried by time or heat. Of course, 

 they are now filled with air, and are firmly enough attached to the 

 slide, and can be covered in a cell if a dry mount is desired. 



To mount in balsam, however, the air must be again extracted, 

 and at this stage the boiled water prescription cannot be administered. 

 Have Canada balsam made quite tough by age or heat, and then 

 dissolved in benzole. Put around the objects which have been dried 

 on the slide a few fragments of cover-glass, and on them, as legs 

 to a stool, place a clean cover-glass. A drop of the pure benzole 

 will quickly run under the cover-glass, and very promptly take the 

 place of the air in the diatoms ; and a drop of the balsam at one 

 edge of the cover, and a corner of blotting-paper at the other, will 

 quickly substitute the balsam for the benzole. Time or gentle heat 

 will harden the cement, and the specimen is safe." 



Cleaning and Preparing Diatom Material— Mounting Diatoms.— 

 Herr E. Debes, in an article of 17 pages, t describes the necessary 



* Amer. Natural., xix. (1885) p. 526. 



t Amer. Mon. Micr. Journ., v. (1884) p. 18. 



j Hedwigia, xxiv. (1885) pp. 49-66. 



