724 SUMMARY OP CURRENT RESEARCHES RELATING TO 



figures, an eye-piece micrometer will be found very useful, not only 

 in selecting diatoms of uniform size, but also in determining tbeir 

 position. A circle ruled in squares and used in the same way as the 

 eye-piece micrometer will be found still more desirable. It is a good 

 idea to keep a number of glass points, of different degrees of fineness, 

 ready prepared ; that is, attached to little rolls of beeswax, so that if a 

 point is unsuited for a particular work another can be substituted in 

 a moment." 



Messrs. Sidle have also modified the mechanical finger described 

 ante, Vol. II. (1879) p. 952, by adding a micrometer-screw with a 

 milled-head nut for moving the point of the glass thread in and out 

 of focus, thus avoiding unscrewing the front of the objective. The 

 sliding rod has been retained for getting it approximately into position. 

 By a later improvement the glass " hair" or bristle is carried on a second 

 rod through a sleeve attached to the first or vertical one, nearly at 

 right angles. Thus, by the rotation of the second rod, and of the 

 entire apparatus around the axis of the Microscope, the diatom may 

 be brought into any desired position. 



Venice Turpentine as a Cement.* — Professor C. B. Parker says 

 that his attention was called to a substance known in the Pathological 

 Laboratory, at Vienna, as Venedischer Damarlack (Venetian dammar 

 varnish), which was exclusively used for sealing and finishing 

 glycerine mounts. No such substance is known to the American 

 trade, but he found after experimenting that Venice turpentine, 

 prepared as presently to be described, if not identical, at least answers 

 every purpose equally as well. The following are the directions for 

 preparing the turpentine. Dissolve true Venice turpentine in enough 

 alcohol, so that after solution it will pass readily through a filter, 

 and, after filtering, place in an evaporating dish, and by means of 

 a sand bath evaporate down to about three-quarters of the quantity 

 originally used. The best way to tell when the evaporation has gone 

 far enough, is to drop some of the melted turpentine, after it is 

 evaporated down to about three-quarters its original volume, into cold 

 water, and on being taken out of the water if it is hard, and breaks 

 with a vitreous fracture on being struck with the point of a knife, 

 cease evaporation and allow to cool. 



Square covers should be used, and the cover-glass being adjusted 

 with the usual precautions observed in glycerine mounting, the 

 surplus glycerine, if any, should be wiped away, and the slide so 

 placed that the edges of the cover-glass are plainly seen. A piece 

 of wire, No. 10-12 (copper is the best, as it gives to the turpentine 

 a greenish tinge), is bent at right angles, the short arm being just 

 the length of the cover-glass. The wire is heated in the flame of an 

 alcohol lamp, and plunged into the prepared turpentine, some of 

 which adheres to it. The wire is then brought down flat upon the 

 slide at the margin of the cover, and the turpentine will distribute 

 itself evenly along the entire side of the cover. The same process is 

 to be carried out on each of the other three sides. Any little uneven- 

 ness may be removed by passing the heated wire over it. 

 * Amer. Mon. Micr. Joura., ii. (1881) pp. 229-30. 



