238 BOTANICAL GAZETTE [march 



the freezing mixture is put in, the 2 pails should balance. An important 

 though simple detail is the proper adjustment of the brace to hold one 

 of the pails up until the water runs through the tubes and freezing box 

 into the other pail. This, as is shown in the accompanying illustration, 

 is made of a piece of hard wood about o. 75 inch square, fastened at the 

 upper end to the wheel by a heavy screw, the hole in the brace being 

 large enough so that it may move freely. The brace must be long 

 enough for its lower end to rest on the cross bar when the lower pail 

 is kbout 3 inches above the base board. When the lower pail receives 

 over half of the water it will move slowly to the base board, the lower 

 end of the brace will pass over the cross bolt and hang perpendicularly 

 by the side of the higher pail. As soon as this pail is emptied it should 

 be lowered, and this should be attended to with promptness, for it is 

 necessary that the water be kept in constant circulation to obtain the 

 maximum freezing efficiency. 



. A very important part of the apparatus of course is the freezing 

 chamber. This will have to be made to order to fit the particular micro- 

 tome one is using, and the size depends upon one's needs. The one 

 which seems to be of general use and which is employed by the writer is 

 constructed as follows: A rod of brass about 2 . 25 inches long is hollowed 

 out about 1 inch deep for the chamber, leaving walls thick enough so 

 that a firm cap can be screwed on. The other end of the rod is trimmed 

 down, making a stem of the desired size to fit the particular microtome. 

 Two tubes with inside diameters 7-8 mm. and o. 75 inch long are welded 

 into the chamber a few millimeters apart on one side. The faucets, 

 one in each pail, should be large enough for a free flow of the water into 

 the tubes and should be shielded on the inside of the pail by copper 

 gauze. A second faucet should be put into one pail to be used to 

 remove surplus water. 



The freezing chamber, of course, must be in a horizontal position 

 while the object is being frozen. A half gallon bottle with a hole in the 

 cork large enough to receive the stem as shown in the illustration is very 

 convenient. 



It is highly desirable to have a section collector if one is cutting 

 much material. This may be made of a block of wood about 1 inch thick, 

 hollowed out on one side, leaving enough margin on 3 edges around the 

 cavity so that it will fit snugly against the knife, a little vaseline being 

 used to prevent leaking. The box may be clamped on in various ways. 



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