E. IF. Morley — Self- Acting Mercurial Air pump. 443 



obtains in f the upper level of the mercury is at a a. The 

 small tube c c is bent upward again, widened at d, and con- 

 tinued upward in e. When the pump is in action, the space 

 above a a is a tolerable vacuum except when tilled with mer- 

 cury. If now air rises with the entering mercury, it is caught 

 in the bend above a: it is driven into c, forced out to d, and 

 escapes through e. This being repeated at every stroke of the 

 major pump, no such accumulation of air can take place above 

 a as to make possible its passage down h and up i. This 

 device not only enables me to transfer gas from one vessel to 

 another without admixture, but it contributes to the ease of 

 making high vacua. Some of my work would have been im- 

 possible without it. 



Discharge of Toepler pump with no compression. 



When a Geissler pump is furnished with three stopcocks as 

 is usual now, the pump body is emptied not into the atmo- 

 sphere but into a good vacuum, and, what is important, the 

 air is discharged without resistance and without consequent 

 compression to a very small volume. But when a Toepler 

 pump is discharged, even with any auxiliary vacuum hereto- 

 fore described (as far as is known to me), the discharge takes 

 place against the pressure of a short column of mercury, and 

 the air is therefore compressed. There accordingly comes a 

 time when this compressed air has no longer a volume suffi- 

 cient to ensure its discharge. For instance, one of my pumps 

 will carry an exhaustion to about one part in five million. The 

 amount to be discharged becomes at this tenuity so small that 

 its volume when compressed forms only a little bubble adher- 

 ing to the side of the tube through which it ought to be dis- 

 charged. But in my laboratory a device has been used for 

 many years which empties the Toepler pump as completely as 

 the Geissler pump is emptied ; and lately this device has been 

 made self-acting. It so much increases the degree of exhaus- 

 tion which can be attained that it may be useful for some pur- 

 poses, and is shown in fig. 3. Tc is an enlargement of the tube 

 by which air is discharged from g. It is connected by a small 

 glass tube with I: the tube is so flexible that I can be moved 

 also into the dotted position. To explain its action, let us sup- 

 pose that the pump is filled with mercury to m, and that I and 

 the slender connecting tube are also so filled. When now g is 

 emptied of mercury, I having been placed in the dotted posi- 

 tion, will remain filled with mercury to the level of the upper 

 dotted line, and k will be shut off from g. Li now I is raised 

 to the upper position, mercury will run out of it, but the pas- 

 sage from g to k will remain closed. Now, when the mercury 



Am. Jour. Sci.— Third Series, Vol. XLVII, Xo. 282.— June, 1894. 

 30 



