404 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
nickel-plated, consists of the two shanks belonging to the two blades, 
and a metal piece between them, which in longitudinal section forms a 
very acute-angled isosceles triangle. To the base of this is attached a 
rod provided with a screw-thread which works in a nut at the end of 
the handle. By means of the screw the rod and, with it, the metal 
prism can be moved up and* down ; the effect of this is to separate the 
Fig. 33. 
knife-handles, and therefore also the blades, more or less apart. A 
second nut at the side, by means of a strong spring acting on one handle 
and a pin on the other, serves to fix the blades in the required position, 
and at the same time to make them practically parallel. The parallel 
position is not mathematically exact, but is sufficiently so for many 
purposes. The knife can be easily taken to pieces to be cleaned. 
Imbedding Delicate Objects in Celloidin. * — Dr. A. Elsching re- 
commends that very delicate objects should be immersed in thin celloidin 
solution for 3-8 days. They are then placed in a glass capsule on the 
bottom of which the necessary description has been already marked with 
a coloured oil-pencil. Thick celloidin solution is then poured over them 
and the capsule closed with a glass plate smeared with thin celloidin 
solution. This effectually excludes the air, though it is advisable to 
cover the apparatus with a bell-jar in case of accidents. In 24 hours 
air-bubbles are removed by turning the preparation over with a needle 
dipped in the thin solution, and then reclosing the capsule as before. 
After a few hours, all the air-bubbles will have disappeared and then 
the capsules may be closed with a dry glass plate. In a few days the 
celloidin will have become stiff enough to be completely set in 85 per 
cent, spirit. 
Air- and Water-free Celloidin Solutions.! — It is important, says 
Dr. A. Elsching, that celloidin solutions should be free from air and 
water. To effectually deprive celloidin of water, the tablets should be 
cut up into little blocks, the sides of which are not bigger than 5 mm. 
These are placed between folds of blotting-paper, and first allowed to 
dry at the room temperature, and then desiccated in an incubator. At 
this stage they should be of a yellowish hue and of horny consistence. 
Absolute alcohol may be easily obtained entirely free of water, by re- 
peated treating with freshly dried copper sulphate. The dried cubes 
are placed in a narrow-necked bottle, with air-tight stopper, and form a 
layer not exceeding one-fourth the volume of the bottle. The celloidin 
is then just covered with absolute alcohol, and allowed to stand for about 
24 hours, after which the ether is poured in. In a very short time the 
celloidin is all dissolved, and thus, as no stirring is required, the solution 
is kept free of air-bubbles. 
Zeitschr. f. wiss. Mikr., x. (1893) pp. 445-6. 
t Tom. cit., pp. 443-5. 
