1102 SUMMARY OF CURRENT RESEARCHES RELATING TO 



a thin syrup, and filter ttrough absorbent cotton. Into a small 

 porcelain capsule put a small quantity of chemically pure zinc oxide, 

 free from moisture (a precaution which is very important and which 

 is best secured by heating the oxide in a muffle for a short time prior 

 to making use of it), and having previously wet it with a small 

 quantity of benzol, add sufficient of the damar solution to make a 

 paste the consistency of cream, or of thick paint. Eub with the 

 muller or pestle until perfectly smooth, and then pour into a stock 

 bottle. Eepeat the operation until a sufficient amount of the cement 

 is obtained. The material should now be allowed to stand until the 

 zinc has separated and sunk to the bottom, and when this has occurred, 

 enough of the damar solution should be added to make the fluid about 

 equal the bulk of the precipitated zinc. Shake up again until the 

 zinc is thoroughly mixed with the damar solution, and filter through 

 a thin layer of absorbent cotton, to get rid of the grosser particles of 

 zinc which escaped the action of the muller. The operation is 

 finished by the addition of a small amount of some drying oil, to give 

 the cement a proper toughness. Some persons use boiled or clarified 

 linseed-oil for this purpose, but it is apt to make the cement " stringy," 

 and hence good nut or poppy-oil is preferable. The amount added 

 should not be over 12 or 15 minims to the ounce of cement. If too 

 much of the damar solution has been added, it is easily got rid of by 

 decantation, after allowing the zinc to separate by standing a few 

 days in a quiet place. If the cement becomes thick after using 

 a while, cut it with pure benzol — not benzin under any circumstances, 

 nor impure benzol. 



Dr. James also writes : — " Since wi'iting and printing the foregoing, 

 I have had occasion to make up quite a large amount of the cement, and 

 have improved the processes somewhat. The principal point in which 

 I have made a change is in doing away with the filtering process, as 

 it is troublesome, slow, and wasteful. I now obtain better results by 

 decantation. After mixing the cement as directed, I give it a vigorous 

 shaking and set the vessel containing it in a quiet place. In the 

 course of a few hours the grosser particles will have sunk to the 

 bottom, and the cement, thus freed from them, may be decanted into 

 other bottles. By repeating this process two or three times, a cement 

 of the most exquisite fineness and finish may be obtained." 



Leakage of Cells.* — On the cause of the leakage of cells, Dr. 

 F. L. James writes as follows : — 



" Many microscopists are in the habit of making their cells only 

 when they are needed, allowing the rings to dry just so much that 

 the cover-glass will not stick when applied. Some do this from 

 thoughtlessness, or rather from never having experimented or inves- 

 tigated the relative merits of a fresh and thoroughly dried and sea- 

 soned cell. Others claim actual advantages for this procedure. 

 They say that wh§n the cover-glass is applied while the cell rings 

 are yet plastic, a more accurate coaptation, or fit, is obtained. It is 

 also claimed that a more homogeneous mass is made with the cement 

 which is subsequently applied to seal the cell. 



* St. Louis National Druggist, vii. (1885) p. 181. 



