454 suaniARY of current researches relating to 



have thouglit that a few hints on the mode of preparing such cells 

 might interest others. 



The porosity of ordinary pajDer is of course an insuperable bar to 

 its employment for cells intended to be filled with watery or even 

 with resinous or oily media ; but when the porosity is got rid of, the 

 facility with which cells may be made of pai>er of varying thickness 

 renders them very convenient. The paper may be rendered perfectly 

 non-absorbent if it is saturated with a resinous substance, which should 

 at the same "time maintain, when diy and hard, its adhesion to the 

 glass. 



Paper used for this purpose should be more or less spongy or 

 porous, such as ordinaiy printing paper, or the cheaper kinds of 

 writing paper, and the cells when made should be allowed to soak for 

 some time in the resinous menstruum, until they are completely satu- 

 rated with it. When in this condition they should be taken out 

 dripping, and placed in proper position on the slide, care being taken 

 that no air-bubbles are left between the j)aper and the glass. 



There are, no doubt, numerous compounds that may be used as the 

 cement. That which I have found convenient and suitable for the 

 purpose of satui-ating the paper, and insuring its permanent adhesion 

 to the glass, is the ordinary solution of canada-balsam-resin in benzole. 

 But when used for this purpose the balsam should not have been com- 

 pletely desiccated, otherwise a little turpentine should be added to the 

 solution. 



The cells should be allowed to diy and harden for several days, 

 when the superfluous balsam can be washed off with a little benzole 

 and sjjirit. 



These cells are perhaps particularly adapted for watery media, 

 such as glycerine or Farrant's medium, but they serve very well also 

 for balsam or castor-oil. Of these media, it seems to me that Farrant's 

 is the most generally useful and most convenient in use. 



In conclusion I may remark that, in mounting an object, great 

 convenience will be found in the use of a small lead weight (2 or 3 oz.) 

 supported on three short pins. This allows of the cleaning of the 

 edges of the cover-glass, and the application of varnish of any kind to 

 fix the glass and jn-event the entrance of air. After having been kept 

 for a day or two under the weight, the cell may be finished off in any 

 way that may be desired. But there is one point with respect to 

 the finishing off that should be noticed if the usual zinc-white paint 

 is employed. This material appears to possess a great power of in- 

 sinuating itself under the cover, and thus disfiguring the prejjaration, 

 if the cell has been merely sealed with a resinous cement. The evil, 

 however, can be completely avoided by the application over the cement 

 of a little gum-mucilage, through which, when dry, the zinc- white has 

 no power of penetration." 



Making Tinfoil Cells.* — Professor A, H. Chester believes that 

 cells from pure tinfoil satisfy better than any others the conditions 



* Proc. Amer. Soc. Micr., 5tli Ann. Meetiog, 1882, pp. 282-3. See also this 

 Journal, i. (1881) pp. 702-3. 



