1891.] MICROSUOPICAL JOURNAL. 7 



A Dehydrating Apparatus. 



By M. B. THOMAS, 



BOTANICAL LAB., CORNELL UNIV., ITHACA, N. Y. 



[See Frontispiece.] 



A very convenient form of Schultze's dehydrating apparatus can be 

 made as follows : 



In a 9 X 9 inches Whitall-Tatum niuseum jar a disk of plaster of Paris 

 is supported about 3 cm. from the top by means of legs made of glass 

 rods (Fig. i , A and C.) The disk is perforated to allow tubes of various 

 sizes varying from 2 to 4 cm. in diameter to pass through. These are 

 the so-called dehydrating tubes. (Fig. i,B.) The plaster of Paris dia- 

 phragm can be made by first making a mould of the desired size with 

 a paper bottom and a card-board hoop for the outside. This must be 

 jDlaced on a level surface. The plaster of Paris is then softened with 

 water and poured into the mould to about the depth of i^ cm. While 

 it is yet soft the three legs can be inserted near the edge, and holes for 

 the dehydrating tubes cut in the disk with a knife, or pressed out with 

 glass tubingof convenient size. When the plaster of Paris is thoroughly 

 dry the hoop can be removed and the disk placed in position in the jar. 



The jar is then filled with alcohol to about 2 cm. of the under side 

 of thedisk. Thedehydratingtubesshouldbe about I3 cm. long, and can 

 be made by cutting off" the bottom of large test tubes. At the bottom 

 is placed a diaphragm of chamois skin, which can be fastened in place 

 by means of a spring made of steel wire, and forced inside of the chamois 

 skin in the tube, thus pressing the former firmly against the latter (Fig. 

 2.) A rubber band around the tubes prevents them from falling 

 through the holes in the disk, and enables them to be lowered to any 

 desired depth in the alcohol. 



The tissue to be dehydrated is packed closely in the dehydrating tube, 

 and enough 50 per cent, alcohol poured over it to just cover it. It is 

 then lowered through the hole in the disk until the two liquids are at 

 a level. After from 12 to 24 hours the two liquids will be of the same 

 sti-ength. The tissue can then be taken out and placed in the infiltrat- 

 ing bath at once. 



This method for hardening has been tried in the Bot. Lab. at Cor- 

 nell University on nearly all kinds of plant tissue, and in every case it 

 was found to be successful. For the most delicate tissue where slow 

 hardening is desired, 5% alcohol can be placed in the dehydrating 

 tube and thick chamois skin used for a diaphragm and for some of the 

 more delicate algte it has been found advisable to use as low as 1% 

 alcohol in the tube. The strength of the alcohol in the jar can be kept 

 up by adding to it from time to time some calcium chloride. This will 

 not injure the alcohol in the least. 



The jar should be tall enough to allow the cover to be kept on while 

 the tubes are in position, and thus prevent evaporation of the alcohol. 

 An apparatus of such a form having 13 dehydrating tubes has been in 

 nearly constant use in the Bot. Dep. for a year without changing the 

 alcohol, and is yet in good working order. 



Experiments have been made with one of smaller size, and it is found 

 that all hardening agents such as picric, chromic, acetic, or osmic acid 

 can be used in it with equal success. 



