FOR USE WITH ETHER AS THE ['FREEZING AGENT. 



295 



forced as a jet of spraj through the hole in the cone, and so on to 

 the under service of the plate I. This is roughened in the form of 

 teeth for the purpose of presenting a larger area to be acted upon, 

 and also to facilitate drainage. A great deal of the Ether drops 

 down into the chamber, and is used again, but a little passes out 

 mingled with the air in such a finely atomized condition that it 

 seems to be impossible to collect it, as I had hoped to be able to do, 

 and is therefore conveyed along the tube H to the external air. 



The advantages possessed by this form of the machine over the 

 old one (used with ice and salt) are that all mess is avoided ; that 

 Ether can always be kept at hand, whereas sometimes it is not 

 possible to procure ice ; that while in all Ether freezing machines 

 with which I am acquainted the vapour must necessarily be inhaled 

 by the operator, in this one such discomfort is entirely obviated 

 except just during the filling of the chamber. Common Methylated 

 Ether, of '730 specific gravity, answers perfectly, though it must 

 be borne in mind that the greater the specific gravity the greater 

 is the force required in pumping. The labour of pumping may be 

 reduced by placing the ball pump between two pieces of wood hinged 

 together like a pair of lemon-squeezers (Fig. 2, A, B, C). The 

 outer board (A, B) 

 should be a fixture, and 

 the other (B, C) be 

 worked by an eccentric 

 (D) acting against a 

 small roller (E), the 

 eccentric being driven 

 by a treadle ; or the 

 action may be made 

 automatic by using a 

 steam engine or other 

 motive power. I have '^'^'>'^'n\v^ 

 been using a small Thirlmere Water Motor with perfect success. As 

 an instance of the freezing power of this apparatus, it may be mentioned 

 that material has been frozen in a room at 96*^ F., using Ether of .730 

 specific gravity, the pump being worked either by hand or with the 

 motor. In conclusion, I beg to tender my best thanks to Mr. J. 

 Swift, to whom is due the credit of working out all the details of 

 the microtome. 



